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Calcium Concentration (calcium + concentration)
Kinds of Calcium Concentration Selected AbstractsAlteration of Ca2+ -ATPase activity in the homogenate, plasma membrane and microsomes of the salivary glands of streptozotocin-induced diabetic ratsCELL BIOCHEMISTRY AND FUNCTION, Issue 3 2009José Nicolau Abstract Diabetes has been implicated in the dryness of the mouth, loss of taste sensation, sialosis, and other disorders of the oral cavity, by impairment of the salivary glands. The aim of the present study was to examine the plasma membrane, microsomal, and homogenate Ca2+ -ATPase activity in the rat submandibular and parotid salivary glands of streptozotocin-induced diabetes. We have also examined the influence of the acidosis state on this parameter. Diabetes was induced by an intraperitoneal injection of streptozotocin and acidosis was induced by daily injection of NH4Cl. At 15 and 30 days after diabetes induction, the animals were euthanized and the submandibular and parotid salivary glands were removed and analyzed. Ca2+ -ATPase (total, independent, and dependent) was determined in the homogenate, microsomal, and plasma membranes of the salivary glands of diabetic and control rats. Calcium concentration was also determined in the glands and showed to be higher in the diabetic animals. Ca2+ -ATPase activity was found to be reduced in all cell fractions studied in the diabetic animals compared with control. Similar results were obtained for the submandibular salivary glands of acidotic animals; however in the parotid salivary glands it was found an increase in the enzyme activity. Copyright © 2009 John Wiley & Sons, Ltd. [source] Variability of Isotope and Major Ion Chemistry in the Allequash Basin, WisconsinGROUND WATER, Issue 7 2003John F. Walker As part of ongoing research conducted at one of the U.S. Geological Survey's Water, Energy, and Biogeochem-ical Budgets sites, work was undertaken to describe the spatial and temporal variability of stream and ground water isotopic composition and cation chemistry in the Trout Lake watershed, to relate the variability to the watershed flow system, and to identify the linkages of geochemical evolution and source of water in the watershed. The results are based on periodic sampling of sites at two scales along Allequash Creek, a small headwater stream in northern Wisconsin. Based on this sampling, there are distinct water isotopic and geochemical differences observed at a smaller hillslope scale and the larger Allequash Creek scale. The variability was larger than expected for this simple watershed, and is likely to be seen in more complex basins. Based on evidence from multiple isotopes and stream chemistry, the flow system arises from three main source waters (terrestrial-, lake-, or wetland-derived recharge) that can be identified along any flowpath using water isotopes together with geochemical characteristics such as iron concentrations. The ground water chemistry demonstrates considerable spatial variability that depends mainly on the flow-path length and water mobility through the aquifer. Calcium concentrations increase with increasing flowpath length, whereas strontium isotope ratios increase with increasing extent of stagnation in either the unsaturated or saturated zones as waters move from source to sink. The flowpath distribution we identify provides important constraints on the calibration of ground water flow models such as that undertaken by Pint et al. (this issue). [source] Decomposition of litter in a dry sclerophyll eucalypt forest and a Pinus radiata plantation in southeastern AustraliaHYDROLOGICAL PROCESSES, Issue 17 2002R. H. Crockford This study of litter decomposition was part of an extensive project examining the partitioning of rainfall, the associated chemistry, and litterfall in a dry sclerophyll eucalypt forest and a Pinus radiata plantation in southeastern Australia. The eucalypt species studied were Eucalyptus rossii, E. mannifera and E. dives. The components tested were Pinus radiata needles, leaves of the three eucalypt species, and the bark of E. rossii and E. mannifera. During the first 16 weeks of the decomposition experiment there was a rapid decrease in the concentrations of potassium, magnesium, sodium and phosphorus; this was attributed to leaching. During this period, concentrations of nitrogen and calcium increased for most components. After this period, decomposition became the dominant process, during which the concentrations of most elements increased. By the end of the experiment there was, compared with the initial values, a marked reduction in concentrations of sodium, magnesium and potassium for all eucalypt and pine litter. Calcium concentrations increased through time, with eucalypt bark showing a mid-period decline. Phosphorus concentrations decreased for the eucalypt leaves but increased substantially for the pine needles and the eucalypt bark. For all components of both the eucalypts and pines, total nitrogen concentrations rose consistently throughout the decomposition period. This was attributed to the formation of nitrogen-substituted lignin, which was more resistant to decomposition than the other nitrogen-containing compounds, as well as some nitrogen being stored in the micro-organisms responsible for decomposition. Because of loss of fragmented litter from the litter bags after 16 weeks, the weight changes could not be confidently measured after this period. Copyright © 2002 John Wiley & Sons, Ltd. [source] Role of the Na+/Ca2+ exchanger in calcium homeostasis and human sperm motility regulationCYTOSKELETON, Issue 2 2006Zoltán Krasznai Abstract A number of cell functions, such as flagellar beating, swimming velocity, acrosome reaction, etc., are triggered by a Ca2+ influx across the cell membrane. For appropriate physiological functions, the motile human sperm maintains the intracellular free calcium concentration ([Ca2+]i) at a submicromolar level. The objective of this study was to determine the role of the Na+/Ca2+ exchanger (NCX) in the maintenance of [Ca2+]i in human spermatozoa. Spermatozoa maintained in extracellular medium containing ,1 ,M Ca2+ exhibited motility similar to that of the control. In addition to several calcium transport mechanisms described earlier, we provide evidence that the NCX plays a crucial role in the maintenance of [Ca2+]i. Three chemically unrelated inhibitors of the NCX (bepridil, DCB (3,,4, -dichlorobenzamil hydrochloride), and KB-R7943) all blocked human sperm motility in a dose and incubation time dependent manner. The IC50 values for bepridil, DCB, and KB-R7943 were 16.2, 9.8, and 5.3 ,M, respectively. The treatment with the above-mentioned blockers resulted in an elevated [Ca2+]i and a decreased [Na+]i. The store-operated calcium channel (SOCC) inhibitor SKF 96365 also blocked the sperm motility (IC50 = 2.44 ,M). The presence of the NCX antigen in the human spermatozoa was proven by flow cytometry, confocal laser scanning microscopy, and immunoblotting techniques. Calcium homeostasis of human spermatozoa is maintained by several transport proteins among which the SOCC and the NCX may play a major role. Cell Motil. Cytoskeleton 2006. © 2005 Wiley-Liss, Inc. [source] Pre-activation of retinoid signaling facilitates neuronal differentiation of mesenchymal stem cellsDEVELOPMENT GROWTH & DIFFERENTIATION, Issue 5 2010Yang Bi Mesenchymal stem cells (MSCs) can differentiate into neurons in an appropriate cellular environment. Retinoid signaling pathway is required in neural development. However, the effect and mechanism through retinoid signaling regulates neuronal differentiation of MSCs are still poorly understood. Here, we report that all-trans-retinoic acid (ATRA) pre-induction improved neuronal differentiation of rat MSCs. We found that, when MSCs were exposed to different concentrations of ATRA (0.01,100 ,mol/L) for 24 h and then cultured with modified neuronal induction medium (MNM), 1 ,mol/L ATRA pre-induction significantly improved neuronal differentiation efficiency and neural-cell survival. Compared with MNM alone induced neural-like cells, ATRA/MNM induced cells expressed higher levels of Nestin, neuron specific enolase (NSE), microtubule-associated protein-2 (MAP-2), but lower levels of CD68, glial fibrillary acidic protein (GFAP), and glial cell line-derived neurotrophic factor(GDNF), also exhibited higher resting membrane potential and intracellular calcium concentration, supporting that ATRA pre-induction promotes maturation and function of derived neurons but not neuroglia cells from MSCs. Endogenous retinoid X receptors (RXR) RXR, and RXR, (and to a lesser extent, RXR,) were weakly expressed in MSCs. But the expression of RAR, and RAR, was readily detectable, whereas RAR, was undetectable. However, at 24 h after ATRA treatment, the expression of RAR,, not RAR, or RAR,, increased significantly. We further found the subnuclear redistribution of RAR, in differentiated neurons, suggesting that RAR, may function as a major mediator of retinoid signaling during neuronal differentiation from MSCs. ATRA treatment upregulated the expression of Vimentin and Stra13, while it downregulated the expression of Brachyury in MSCs. Thus, our results demonstrate that pre-activation of retinoid signaling by ATRA facilitates neuronal differentiation of MSCs. [source] Stable strontium accumulation by earthworms: A paradigm for radiostrontium interactions with its cationic analogue, calciumENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2001John E. Morgan Abstract The accumulation of stable strontium and its chemical analogue calcium by four species of earthworm, representing three distinct ecophysiological groups inhabiting celestite (SrSO4)-rich natural soils, was investigated. An increase in soil strontium concentration over a four-orders-of-magnitude range was accompanied by an increase in earthworm tissue strontium concentration. In contrast, no relationship between soil and tissue calcium concentrations was apparent, indicating that this essential cation is strongly regulated within earthworm tissues but that nonessential strontium burdens are not physiologically regulated. Concentration factors for strontium ranged from 0.1 to 1.42, with an inverse relationship between this parameter and soil strontium concentration. The use of concentration factors and discrimination coefficients lead to the conclusion that earthworms discriminate against strontium accumulation at increased soil calcium concentrations, such that strontium would be predicted to be more efficiently accumulated by worms inhabiting acidic, calcium-poor soils. Although few consistent trends in strontium and calcium concentration were apparent between earthworm species, the species with the highest calcium turnover (i.e., the litter-inhabiting Lumbricus rubellus) typically accumulated higher concentrations of strontium than representatives of contrasting ecophysiological classes. These findings are considered in the context of the distribution, retention, and cycling of radiostrontium in soils. [source] Constrained multivariate trend analysis applied to water quality variablesENVIRONMETRICS, Issue 1 2002D. M. Cooper Abstract Constrained multivariate regression analysis is used to model trends and seasonal effects in time series measurements of water quality variables. The constraint used ensures that when identifying trends the scientifically important charge balance of model-fitted concentrations is maintained, while accounting for between variable dependencies. The analysis is a special case of linear reduction of dimensionality which preserves the integrity of a subset of the original variables, while allowing the remainder to be identified as linear combinations of this subset. The technique is applied to water quality measurements made at the outflow from Loch Grannoch, an acid-sensitive loch in Scotland. A reduction in marine ion concentrations is observed in water samples collected four times a year over the period 1988,2000. This is identified with long term variability in the marine component in rainfall. Separation of the non-marine component of the solute load shows a reduction in non-marine sulphate and calcium concentrations, and an increase in the non-marine sodium concentration. There is no significant change in either alkalinity or acid neutralizing capacity over the period. The reduction in non-marine sulphate is consistent with reductions in atmospheric inputs of sulphate. However, the reduction in sulphate has not been accompanied by a reduction in the acidity of water samples from Loch Grannoch, but with a reduction in calcium concentration and an apparent increase in organic acids, as evidenced by increased dissolved organic carbon concentrations, with possible increases in nitrate and non-marine sodium concentrations. Copyright © 2002 John Wiley & Sons, Ltd. [source] Vitamin D and calcium deficits predispose for multiple chronic diseasesEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 5 2005M. Peterlik Abstract There is evidence from both observational studies and clinical trials that calcium malnutrition and hypovitaminosis D are predisposing conditions for various common chronic diseases. In addition to skeletal disorders, calcium and vitamin D deficits increase the risk of malignancies, particularly of colon, breast and prostate gland, of chronic inflammatory and autoimmune diseases (e.g. insulin-dependent diabetes mellitus, inflammatory bowel disease, multiple sclerosis), as well as of metabolic disorders (metabolic syndrome, hypertension). The aim of the present review was to provide improved understanding of the molecular and cellular processes by which deficits in calcium and vitamin D cause specific changes in cell and organ functions and thereby increase the risk for chronic diseases of different aetiology. 1,25-dihydroxyvitamin D3 and extracellular Ca++ are both key regulators of proliferation, differentiation and function at the cellular level. However, the efficiency of vitamin D receptor-mediated intracellular signalling is limited by the negative effects of hypovitaminosis D on extrarenal 25-hydroxyvitamin D-1,-hydroxylase activity and thus on the production of 1,25-dihydroxyvitamin D3. Calcium malnutrition eventually causes a decrease in calcium concentration in extracellular fluid compartments, resulting in organ-specific modulation of calcium-sensing receptor activity. Hence, attenuation of signal transduction from the ligand-activated vitamin D receptor and calcium-sensing receptor seems to be the prime mechanism by which calcium and vitamin D insufficiencies cause perturbation of cellular functions in bone, kidney, intestine, mammary and prostate glands, endocrine pancreas, vascular endothelium, and, importantly, in the immune system. The wide range of diseases associated with deficits in calcium and vitamin D in combination with the high prevalence of these conditions represents a special challenge for preventive medicine. [source] Differential Ca2+ -dependence of transmitter release mediated by P/Q- and N-type calcium channels at neonatal rat neuromuscular junctionsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2002Marcelo D. Rosato-Siri Abstract N- and P/Q-type voltage dependent calcium channels (VDCCs) mediate transmitter release at neonatal rat neuromuscular junction (NMJ). Thus the neonatal NMJ allows an examination of the coupling of different subtypes of VDCCs to the release process at a single synapse. We studied calcium dependence of transmitter release mediated by each channel by blocking with ,-conotoxin GVIA the N-type channel or with ,-agatoxin IVA the P/Q-type channel while changing the extracellular calcium concentration ([Ca2+]o). Transmitter release mediated by P/Q-type VDCCs showed steeper calcium dependence than N-type mediated release (average slope 3.6 ± 0.09 vs. 2.6 ± 0.03, respectively). Loading the nerve terminals with 10 µm BAPTA-AM in the extracellular solution reduced transmitter release and occluded the blocking effect of ,-conotoxin GVIA (blockade ,2 ± 9%) without affecting the action of ,-agatoxin IVA (blockade 85 ± 4%). Both VDCC blockers were able to reduce the amount of facilitation produced by double-pulse stimulation. In these conditions facilitation was restored by increasing [Ca2+]o. The facilitation index (fi) was also reduced by loading nerve terminals with 10 µm BAPTA-AM (fi = 1.2 ± 0.1). The control fi was 2.5 ± 0.1. These results show that P/Q-type VDCCs were more efficiently coupled to neurotransmitter release than were N-type VDCCs at the neonatal neuromuscular junction. This difference could be accounted for by a differential location of these channels at the release site. In addition, our results indicate that space,time overlapping of calcium domains was required for facilitation. [source] Independent receptors for diadenosine pentaphosphate and ATP in rat midbrain single synaptic terminalsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2001M. Díaz-Hernández Abstract Diadenosine pentaphosphate (Ap5A) and adenosine 5,-triphosphate (ATP) stimulate a intrasynaptosomal calcium concentration [Ca2+]i increase via specific purinergic receptors in rat midbrain synaptosomes, although nothing is known about their distribution in presynaptic terminals. A microfluorimetric technique to measure [Ca2+]i increase using the dye FURA-2AM, has permitted study of the presence of dinucleotide and P2X receptors in independent isolated synaptic terminals. Our results demonstrate the existence of three populations of synaptosomes: one with dinucleotide receptors (12%), another with P2X receptors (20%) and a third with both (14%). It has been possible to demonstrate that the activation of these receptors occurs only in the presence of extracellular Ca2+ and that it is also coupled with voltage-dependent Ca2+ channels. Finally 54% of the synaptosomes that responded to K+ did not present any calcium increase mediated by the nucleotides used. In summary, ATP and dinucleotides exhibit specific ionotropic receptors that can coexist or not on the same synaptic terminal. [source] Differential induction of LTP and LTD is not determined solely by instantaneous calcium concentration: an essential involvement of a temporal factorEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2001Tomoyuki Mizuno Abstract Two opposite types of synaptic plasticity in the CA1 hippocampus, long-term potentiation (LTP) and long-term depression (LTD), require postsynaptic Ca2+ elevation. To explain these apparently contradictory phenomena, the current view assumes that a moderate postsynaptic increase in Ca2+ leads to LTD, whereas a large increase leads to LTP. No detailed study has so far been attempted to investigate whether the instantaneous Ca2+ elevation level differentially induces LTP or LTD. We therefore used low-frequency (1 Hz) stimulation of Schaffer collateral/commissural fibers in rat hippocampal slices, during a Mg2+ -free period, as the conditioning stimulus to investigate this. This allowed low-frequency afferent stimulation to cause a postsynaptic Ca2+ influx because the voltage-dependent block of N -methyl- d -aspartate (NMDA) receptor-channels by Mg2+ was removed. When delivered during the Mg2+ -free period, a single pulse, as well as 2,600 pulses, induced LTP that was occluded with tetanus-induced LTP. To decrease the Ca2+ influx, ,-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors were completely blocked by the addition of 10 µm 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) to the conditioning medium, in which 1 Hz afferent stimuli (1,600 pulses) induced less LTP and never induced LTD. To further reduce the Ca2+ influx, NMDA receptors were partially blocked with d -(,)-2-amino-5-phosphonopentanoic acid (d -AP5). A small number of 1 Hz stimuli, however, never induced LTD. Only when the conditioning stimuli exceeded 200 pulses was LTD induced. The present findings provide definitive evidence that protracted conditioning is a prerequisite for the induction of LTD. Thus, not only the amplitude but also the duration of postsynaptic Ca2+ elevation could be essential factors for differentially inducing LTP or LTD. [source] Enamel dissolution in citric acid as a function of calcium and phosphate concentrations and degree of saturation with respect to hydroxyapatiteEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 5 2003Michele E. Barbour The aim of this study was to investigate enamel dissolution in citric acid solutions as a function of solution calcium and phosphate concentrations and degree of saturation with respect to hydroxyapatite (DSHA). The primary relevance of the study is the development of soft drinks with reduced erosive potential. Nanoindentation was used to investigate changes in the hardness of polished human enamel surfaces after 120 s and 300 s exposure to solutions with pH 3.30 and a range of calcium and phosphate concentrations. All solutions were undersaturated with respect to hydroxyapatite, with 0.000 , DSHA , 0.295. A complex dependence of enamel softening on calcium concentration was observed. Substantial enamel softening occurred in solutions with calcium concentrations equal to or less than 120 mm (DSHA , 0.104), but there was little or no statistically significant softening of the enamel for calcium concentrations over 120 mm. This condition may be applicable to soft drink formulation. Furthermore, solutions with DSHA = 0.101 and different calcium/phosphate ratios resulted in different degrees of softening of the enamel. Hence, contrary to assumptions made in many models, enamel dissolution is not simply a function of DSHA, and individual calcium and phosphate concentrations are critical. [source] Hypotonic stress influence the membrane potential and alter the proliferation of keratinocytes in vitroEXPERIMENTAL DERMATOLOGY, Issue 4 2007Mónika Gönczi Abstract:, Keratinocyte proliferation and differentiation is strongly influenced by mechanical forces. We investigated the effect of osmotic changes in the development of HaCaT cells in culture using intracellular calcium measurements, electrophysiological recordings and molecular biology techniques. The application of hypotonic stress (174 mOsmol/l) caused a sustained hyperpolarization of HaCaT cells from a resting potential of ,27 ± 4 to ,51 ± 9 mV. This change was partially reversible. The surface membrane channels involved in the hyperpolarization were identified as chloride channels due to the lack of response in the absence of the anion. Cells responded with an elevation of intracellular calcium concentration to hypotonic stress, which critically depended on external calcium. The presence of phorbol-12-myristate-13-acetate in the culture medium for 12 h augmented the subsequent response to hypotonic stress. A sudden switch from iso- to hypotonic solution increased cell proliferation and suppressed the production of involucrin, filaggrin and transglutaminase, markers of keratinocyte differentiation. It is concluded that sudden mechanical forces increase the proliferation of keratinocytes through alterations in their membrane potential and intracellular calcium concentration. These changes together with additional modifications in channel expression and intracellular signalling mechanisms could underlie the increased proliferation of keratinocytes in hyperproliferative skin diseases. [source] Influence of calcium on the proteolytic degradation of the calmodulin-like skin protein (calmodulin-like protein 5) in psoriatic epidermisEXPERIMENTAL DERMATOLOGY, Issue 6 2006Bruno Méhul Abstract:, The calmodulin-like skin protein (CLSP) or so-called calmodulin-like protein 5, a recently discovered skin-specific calcium-binding protein, is closely related to keratinocyte differentiation. The 16-kDa protein is proteolytically degraded in the upper layers of the stratum corneum (SC) of healthy skin. With the use of specific new monoclonal antibodies to CLSP, we were able to demonstrate that the abnormal elevated levels of CLSP, characteristic of psoriatic epidermis, were probably not due to an overexpression of the protein, but most likely the result of its non-degradation. Further in vitro experiments using recombinant CLSP and in situ data clearly showed that calcium protected and chelator accelerated CLSP degradation. These data indicate that CLSP degradation in the SC of psoriatic skin might be hindered by the abnormally elevated calcium concentration. No degradation of CLSP in psoriatic epidermis keeping its ability to bind protein as transglutaminase 3 may have a physiological role in skin diseases such as psoriasis. [source] NMDA receptors influence the intracellular calcium concen-tration and the expression of differentiation markers in HaCaT cellsEXPERIMENTAL DERMATOLOGY, Issue 9 2004M. Fischer Ionotropic glutamate receptors (ligand-gated, ion-channel proteins) of the N -methyl- d -aspartate (NMDA) receptor type could enable a transmembranous calcium influx from the extracellular space. Though ionotropic glutamate receptors are predominantly neuronal receptors, they are also expressed in non-neuronal tissues like keratinocytes. Therefore, investigations were performed to study the function of NMDA receptors in HaCaT cells. The intracellular calcium concentration of HaCaT cells was studied under the influence of the selective receptor agonist NMDA and the selective NMDA antagonist MK-801. The proliferation of HaCaT cells was investigated using the crystal-violet method. Furthermore, the expression of Cytokeratin 10 and Filaggrin was examined in HaCaT cells after blocking NMDA receptors with MK-801. Using NMDA, there was a significant increase in the number of HaCaT cells showing elevated intracellular calcium concentration, at a dose between 25 µm and 1 mm (up to 84.6% of cells). The NMDA-associated calcium influx could be significantly suppressed by prior application of MK-801. There was no influence of NMDA on the proliferation of HaCaT cells. There was also no cytotoxic effect of NMDA (up to 1 mm). The expression of Cytokeratin 10 and Filaggrin could be suppressed by blocking NMDA receptors with MK-801. The investigations show that glutamate receptors of the NMDA-type play a role in the differentiation of HaCaT cells by regulating their intracellular calcium concentration. [source] Inhibition of carbachol-evoked oscillatory currents by the NO donor sodium nitroprusside in guinea-pig ileal myocytesEXPERIMENTAL PHYSIOLOGY, Issue 4 2005Seung-Soo Chung The effect of sodium nitroprusside (SNP) on carbachol (CCh)-evoked inward cationic current (Icat) oscillations in guinea-pig ileal longitudinal myocytes was investigated using the whole-cell patch-clamp technique and permeabilized longitudinal muscle strips. SNP (10 ,m) completely inhibited Icat oscillations evoked by 1 ,m CCh. 1H-(1,2,4) Oxadiazole [4,3-a] quinoxaline-1-one (ODQ; 1 ,m) almost completely prevented the inhibitory effect of SNP on Icat oscillations. 8-Bromo-guanosine 3,,5,-cyclic monophosphate (8-Br-cGMP; 30 ,m) in the pipette solution completely abolished Icat oscillations. However, a pipette solution containing Rp-8-Br-cGMP (30 ,m) almost completely abolished the inhibitory effect of SNP on Icat oscillations. When the intracellular calcium concentration ([Ca2+]i) was held at a resting level using BAPTA (10 mm) and Ca2+ (4.6 ,m) in the pipette solution, CCh (1 ,m) evoked only the sustained component of Icat without any oscillations and SNP did not affect the current. A high concentration of inositol 1,4,5-trisphosphate (IP3; 30 ,m) in the patch pipette solutions significantly reduced the inhibitory effect of SNP (10 ,m) on Icat oscillations. SNP significantly inhibited the Ca2+ release evoked by either CCh or IP3 but not by caffeine in permeabilized preparations of longitudinal muscle strips. These results suggest that the inhibitory effects of SNP on Icat oscillations are mediated, in part, by functional modulation of the IP3 receptor, and not by the inhibition of cationic channels themselves or by muscarinic receptors in the plasma membrane. This inhibition seems to be mediated by an increased cGMP concentration in a protein kinase G-dependent manner. [source] Calcium modulates endopeptidase 24.15 (EC 3.4.24.15) membrane association, secondary structure and substrate specificityFEBS JOURNAL, Issue 12 2005Vitor Oliveira The metalloendopeptidase 24.15 (EP24.15) is ubiquitously present in the extracellular environment as a secreted protein. Outside the cell, this enzyme degrades several neuropeptides containing from 5 to 17 amino acids (e.g. gonadotropin releasing hormone, bradykinin, opioids and neurotensin). The constitutive secretion of EP24.15 from glioma C6 cells was demonstrated to be stimulated linearly by reduced concentrations of extracellular calcium. In the present report we demonstrate that extracellular calcium concentration has no effect on the total amount of the extracellular (cell associated + medium) enzyme. Indeed, immuno-cytochemical analyses by confocal and electron microscopy suggested that the absence of calcium favors the enzyme shedding from the plasma membrane into the medium. Two putative calcium-binding sites on EP24.15 (D93 and D159) were altered by site-directed mutagenesis to investigate their possible contribution to binding of the enzyme at the cell surface. These mutated recombinant proteins behave similarly to the wild-type enzyme regarding enzymatic activity, secondary structure, calcium sensitivity and immunoreactivity. However, immunocytochemical analyses by confocal microscopy consistently show a reduced ability of the D93A mutant to associate with the plasma membrane of glioma C6 cells when compared with the wild-type enzyme. These data and the model of the enzyme's structure as determined by X-ray diffraction suggest that D93 is located at the enzyme surface and is consistent with membrane association of EP24.15. Moreover, calcium was also observed to induce a major change in the EP24.15 cleavage site on distinctive fluorogenic substrates. These data suggest that calcium may be an important modulator of ep24.15 cell function. [source] Calcium and polyamine regulated calcium-sensing receptors in cardiac tissuesFEBS JOURNAL, Issue 12 2003Rui Wang Activation of a calcium-sensing receptor (Ca-SR) leads to increased intracellular calcium concentration and altered cellular activities. The expression of Ca-SR has been identified in both nonexcitable and excitable cells, including neurons and smooth muscle cells. Whether Ca-SR was expressed and functioning in cardiac myocytes remained unclear. In the present study, the transcripts of Ca-SR were identified in rat heart tissues using RT-PCR that was further confirmed by sequence analysis. Ca-SR proteins were detected in rat ventricular and atrial tissues as well as in isolated cardiac myocytes. Anti-(Ca-SR) Ig did not detect any specific bands after preadsorption with standard Ca-SR antigens. An immunohistochemistry study revealed the presence of Ca-SR in rat cardiac as well as other tissues. An increase in extracellular calcium or gadolinium induced a concentration-dependent sustained increase in [Ca2+]i in isolated ventricular myocytes from adult rats. Spermine (1,10 mm) also increased [Ca2+]i. Pre-treatment of cardiac myocytes with thapsigargin or U73122 abolished the extracellular calcium, gadolinium or spermine-induced increase in [Ca2+]i. The blockade of Na+/Ca2+ exchanger or voltage-dependent calcium channels did not alter the extracellular calcium-induced increase in [Ca2+]i. Finally, extracellular calcium, gadolinium and spermine all increased intracellular inositol 1,4,5-triphosphate (IP3) levels. Our results demonstrated that Ca-SR was expressed in cardiac tissue and cardiomyocytes and its function was regulated by extracellular calcium and spermine. [source] Groundwater biodiversity patterns in the Lessinian Massif of northern ItalyFRESHWATER BIOLOGY, Issue 4 2009DIANA M. P. GALASSI Summary 1. The distribution patterns of stygobiotic invertebrates were examined with a stratified sampling design at 197 sites selected among four hydrogeographic basins in the Lessinian Massif (northern Italy). The sites were approximately evenly distributed among four hydrogeological zones: unsaturated and saturated zone of karstic aquifers, and hyporheic and saturated zone of porous aquifers. 2. Outlying Mean Index (OMI) analysis which assesses deviation of habitat conditions from reference conditions, was used to evaluate the importance of 14 selected environmental variables in shaping groundwater biodiversity patterns in the region (total of 89 stygobiotic species). The measured variables explained 80% of the variability in the data set. 3. Sampling sites were distributed along the environmental gradients defined by OMI analysis. Significant differences were detected between karstic and porous site, as well as among sites located in the four hydrogeological zones. Differences among the four hydrogeographic basins were not observed. 4. Ordination of stygobiotic species along the environmental gradients was best explained by historical variables (mainly Würmian glaciation and age of the underlying geological formation), while variables related to hydrogeology (mainly pH, calcium concentration and habitat fragmentation) influenced species distributions in the hydrogeological zones. An Environmental Integrity Index and nitrate concentration were significantly correlated with altitude, but appeared not to play a significant role in determining stygobiotic biodiversity patterns at the regional scale. 5. Results of the OMI analysis were highly significant for all taxa, suggesting that stygobiotic species are sensitive to the environmental factors studied. Thirty-five species showed high habitat specialisation (OMI index > 10). These species were usually rare and endemic to the Lessinian Massif. Most of them were found in a single hydrogeological zone. 6. Quaternary glaciations appear not to have lowered stygobiotic species richness in the Lessinian Massif. This may be because of the marginal location of the region with respect to the Würmian glacier limit and because of extensive networks of fractures in the vadose zone of the karst, which may have allowed stygobionts to move deep down in the aquifers to seek refuge during surface freezing and to recolonise ancestral habitats after the glaciers retreated. [source] A geomorphic template for the analysis of lake districts applied to the Northern Highland Lake District, Wisconsin, U.S.A.FRESHWATER BIOLOGY, Issue 3 2000JoaN. L. Riera 1. We tested the degree to which a lake's landscape position constrains the expression of limnological features and imposes a characteristic spatial pattern in a glacial lake district, the Northern Highland Lake District in north-central Wisconsin. 2. We defined lake order as a metric to analyze the effect of landscape position on limnological features. Lake order, analogous to stream order, is based solely on geographical information and is simple to measure. 3. We examined the strength of the relationship between lake order and a set of 25 variables, which included measures of lake morphometry, water optical properties, major ions, nutrients, biology, and human settlement patterns. 4. Lake order explained a significant fraction of the variance of 21 of the 25 variables tested with ANOVA. The fraction of variance explained varied from 12% (maximum depth) to 56% (calcium concentration). The variables most strongly related to lake order were: measures of lake size and shape, concentrations of major ions (except sulfate) and silica, biological variables (chlorophyll concentration, crayfish abundance, and fish species richness), and human-use variables (density of cottages and resorts). Lake depth, water optical properties, and nutrient concentrations (other than silica) were poorly associated with lake order. 5. Potential explanations for a relationship with lake order differed among variables. In some cases, we could hypothesize a direct link. For example, major ion concentration is a function of groundwater input, which is directly related to lake order. We see these as a direct influence of the geomorphic template left by the retreat of the glacier that led to the formation of this lake district. 6. In other cases, a set of indirect links was hypothesized. For example, the effect of lake order on lake size, water chemistry, and lake connectivity may ultimately explain the relation between lake order and fish species richness. We interpret these relationships as the result of constraints imposed by the geomorphic template on lake development over the last 12 000 years. 7. By identifying relationships between lake characteristics and a measure of landscape position, and by identifying geomorphologic constraints on lake features and lake evolution, our analysis explains an important aspect of the spatial organization of a lake district. [source] Na,K-ATPase ,2 inhibition alters calcium responses in optic nerve astrocytesGLIA, Issue 3 2004April K. Hartford Abstract Experiments were conducted to test the effect of 1 ,M ouabain, an Na,K-ATPase inhibitor, on capacitative calcium entry (CCE) and calcium responses elicited by ATP in rat optic nerve astrocytes. In the rat, 1 ,M ouabain is sufficient to inhibit the ,2 Na,K-ATPase, but not the ,1. Immortalized astrocytes derived from Na,K-ATPase ,2 homozygous knockout (KO) mice and wild-type (WT) littermates were also used. Cytosolic calcium and sodium concentrations were measured using Fura-2 and SBFI, respectively. The magnitude of the increase in cytosolic calcium concentration during CCE was significantly greater in rat astrocytes exposed to 1 ,M ouabain. To measure calcium release from stores, cells were exposed to ATP in the absence of extracellular calcium. In astrocytes exposed to 1 ,M ouabain, a significantly greater calcium response to ATP was observed. 1 ,M ouabain was shown to inhibit ATP hydrolysis in membrane material containing Na,K-ATPase ,2 and ,1 isoforms (rat muscle) but not in membranes containing only Na,K-ATPase ,1 (rat kidney). In intact astrocytes, 1 ,M ouabain did not alter the cell-wide cytosolic sodium concentration. In mouse Na,K-ATPase ,2 KO astrocytes, the calcium increase during CCE was significantly higher than in WT cells, as was the magnitude of the calcium response to ATP. In KO astrocytes, but not WT, the cytosolic calcium increase during CCE was insensitive to 1 ,M ouabain. Taken together, the results suggest that selective inhibition of the Na,K-ATPase ,2 isoform has the potential to change calcium signaling and CCE. © 2003 Wiley-Liss, Inc. [source] Effects of prolactin on intracellular calcium concentration and cell proliferation in human glioma cellsGLIA, Issue 3 2002Thomas Ducret Abstract Prolactin (PRL) has several physiological effects on peripheral tissues and the brain. This hormone acts via its membrane receptor (PRL-R) to induce cell differentiation or proliferation. Using reverse transcription,polymerase chain reaction (RT-PCR) combined with Southern blot analysis, we detected PRL-R transcripts in a human glioma cell line (U87-MG) and in primary cultured human glioblastoma cells. These transcripts were deleted or not in their extracellular domains. We examined the effects of PRL on intracellular free Ca2+ concentration ([Ca2+]i) in these cells in order to improve our understanding of the PRL transduction mechanism, which is still poorly documented. [Ca2+]i was measured by microspectrofluorimetry using indo-1 as the Ca2+ fluorescent probe. Spatiotemporal aspects of PRL-induced Ca2+ signals were investigated using high-speed fluo-3 confocal imaging. We found that physiological concentrations (0.4,4 nM) of PRL-stimulated Ca2+ entry and intracellular Ca2+ mobilization via a tyrosine kinase,dependent mechanism. The two types of Ca2+ responses observed were distinguishable by their kinetics: one showing a slow (type I) and the other a fast (type II) increase in [Ca2+]i. The amplitude of PRL-induced Ca2+ increases may be sufficient to provoke several physiological responses, such as stimulating proliferation. Furthermore, PRL induced a dose-dependent increase in [3H]thymidine incorporation levels and in cellular growth and survival, detected by the MTT method. These data indicate that PRL induced mitogenesis of human glioma cells. GLIA 38:200,214, 2002. © 2002 Wiley-Liss, Inc. [source] Flowpath Delineation and Ground Water Age, Allequash Basin, WisconsinGROUND WATER, Issue 7 2003Christine D. Pint An analysis of ground water flowpaths to a lake and creek in northern Wisconsin shows the flow system in a geologically simple basin dominated by lakes can be surprisingly complex. Differences in source area, i.e., lakes or terrestrial, combined with the presence of intervening lakes, which may or may not capture underflowing ground water as water moves downgradient from recharge areas, contribute to a complex mix of flowpaths. The result is water of different chemistry and vastly different ages may discharge in close proximity. Flowpaths, travel times, and capture zones in the Allequash Basin in northern Wisconsin were delineated using particle tracking based on a calibrated steady-state ground water flow model. The flowpath analysis supports the conclusions of Walker et al. (2003) who made inferences about flowpath characteristics from isotope and major ion chemistry. Simulated particle tracking agreed with Walker et al.'s measurements of water source (lake or terrestrial recharge) in the stream subsurface and also supported their assertion that ground water with a high calcium concentration in the lower basin of Allequash Lake is derived from long flowpaths. Numerical simulations show that ground water discharging in this area originates more than 5 km away in a source area located upgradient of Big Muskellunge Lake, which is upgradient of Allequash Lake. These results graphically illustrate that in settings with multiple sources of water with different age characteristics and converging flowlines (like the Allequash Basin) it may be difficult to obtain accurate estimates of ground water age by chemical analyses of ground water. [source] Synaptic Transmission: Inhibition of Neurotransmitter Release by Botulinum ToxinsHEADACHE, Issue 2003Oliver Dolly MSc Botulinum toxin type A, a protein long used in the successful treatment of various dystonias, has a complex mechanism of action that results in muscle relaxation. At the neuromuscular junction, the presynaptic nerve ending is packed with synaptic vesicles filled with acetylcholine, and clustered at the tip of the folds of the postsynaptic muscle membrane are the acetylcholine receptors. Synaptic vesicles fuse with the membrane in response to an elevation of intraneuronal calcium concentration and undergo release of their transmitter by exocytosis. Intracellular proteins that contribute to the fusion of the vesicles with the plasma membrane during exocytosis include synaptosomal protein with a molecular weight of 25 kDa (SNAP-25); vesicle-associated membrane protein (VAMP), also known as synaptobrevin; and syntaxin. Through their proteolytic action on these proteins, botulinum toxins prevent exocytosis, thereby inhibiting the release of acetylcholine. There are 7 serotypes of this toxin,A, B, C1, D, E, F, and G,and each cleaves a different intracellular protein or the same target at distinct bonds. The separate cleavage sites in SNAP-25 for botulinum toxin types A and E contribute to their dissimilar durations of muscle relaxation. This report describes the molecular basis for the inhibition by botulinum toxins of neuroexocytosis and subsequent functional recovery at the neuromuscular junction. [source] Requesting patterns for serum calcium concentration in patients on long-term lithium therapyINTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 1 2009B. J. Jones Summary Aim:, Long-term lithium therapy is associated with hypercalcaemia in 10,60% of patients, but unlike creatinine and thyroid stimulating hormone (TSH), monitoring by general practitioners of serum calcium for patients on lithium is not a requirement of the Qualities and Outcomes Framework (QOF) of 2004. We aimed to assess requesting patterns for serum calcium in patients on long-term lithium therapy and subsequent diagnosis of hypercalcaemia. Methods:, We identified 100 patients on long-term lithium therapy, as indicated by regular monitoring of lithium levels in our laboratory for at least 1 year. We determined how many of these patients had had serum calcium analysed, noting the assay date, concentration, source of request and clinical details stated. Results:, Forty-three out of hundred patients had serum calcium analysed during the course of their treatment including 28 in the previous 15 months. Twenty-one patients had serum calcium analysed by their GP, including 12 in the previous 15 months. Hypercalcaemia was diagnosed in five patients (11.6%). Conclusion:, A significant proportion of patients in whom calcium was checked developed hypercalcaemia on lithium therapy. However, only 12% of the patients had serum calcium requested by their GP in the previous 15 months, which compares unfavourably with TSH and creatinine, for which monitoring approaches 100%. We recommend that serum calcium be checked every 15 months along with creatinine and TSH. This might be achieved by incorporating appropriate targets into the QOF, or by reflective or reflex adding-on of calcium to lithium specimens from patients who have not had calcium analysed in the previous 15 months. [source] The effect of addition of calcium and processing temperature on the quality of guava in syrupINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 4 2006Ana Carla K. Sato Summary The effect of process temperature and calcium concentration in the cooking syrup of guava in syrup were studied. A central composite rotatable design (CCRD) was used to optimize the quality indices of the final product, such as texture and colour. All of the processed guava quality parameters were compared with those of the fresh fruit and of a commercial sample to evaluate the effects of processing on the final product quality. Increase in the process temperature promoted changes in the final product colour, the fruit becoming darker. On the contrary, higher calcium concentrations in the cooking syrup produced lighter samples, with colour parameters closer to those of the fresh fruit. In general, the addition of calcium promoted better texture and minimized the negative effects of temperature on the mechanical properties. Processed guavas had higher rupture stress and strain than fresh fruit, indicating an increase in hardness and elasticity. [source] Effect of sodium phytate supplementation on fat digestion and cholesterol metabolism in female ratsJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 11-12 2005C. Yuangklang Summary The effects of sodium phytate supplementation on fat digestion and cholesterol metabolism were investigated in female rats. On the basis of an in vitro experiment showing that phytate raised the solubility of bile acids, it was predicted that phytate feeding would depress faecal bile acid excretion, raise apparent fat digestibility and elevate serum cholesterol concentrations. The experimental diets with or without sodium phytate were either cholesterol-free or cholesterol-rich and had a normal calcium concentration. Rats fed on the cholesterol-rich diet with sodium phytate showed enhanced faecal bile acid excretion, but there was no effect on fat digestibility. In rats fed the cholesterol-free diets, phytate did neither affect fat digestion nor bile acid excretion. Sodium phytate inclusion in the cholesterol-rich diet raised serum cholesterol concentrations, but reduced liver cholesterol concentration. Thus, the in vivo data do not agree with the in vitro observations. Both phytate and cholesterol feeding influenced mineral and trace element metabolism. Liver zinc concentrations were raised by phytate feeding. Cholesterol consumption reduced hepatic concentrations of copper, iron and zinc. Both phytate and cholesterol feeding reduced the apparent absorption of calcium, magnesium and phosphorus. [source] Fractal structure of basic silica gels with low Ca contentJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000F. Gaboriaud Several gels were produced by addition of low amounts of calcium ions to strongly basic silico-alkaline sols. These gels, previously studied by small-angle x-ray scattering (SAXS), small-angle neutron scattering (SANS) and elastic light scattering (ELS), were analysed over a wide range of scattering vectors extending from 8 x 10,4Ĺ,1 up to 2 x 10,4Ĺ. The joint use of various scattering techniques allowed us the simultaneous characterisation of coarse, medium and fine structural features of the studied gels. Clear discrepancies between SANS and earlier ELS results were attributed to effects of multiple scattering on light scattering experiments. The experimental results demonstrate that the studied gels are composed of aggregates exhibiting a fractal structure within a scale range extending from less than 10 to more than 1000 Ĺ, with the same fractal dimension over the whole scale range. The fractal dimension and so the mechanism of aggregation depend on the initial sol composition and Ca content. The mechanism responsible for gel formation in precursor sols with low calcium concentration ([Ca2+] = 0.3 mol.L,1) is reaction limited cluster-cluster aggregation (RLCA). [source] Prostaglandins in rainbow trout (Oncorhynchus mykiss Walbaum, 1792) sperm biology , searching for answersJOURNAL OF APPLIED ICHTHYOLOGY, Issue 4 2008R. K. Kowalski Summary The purpose of this study was to determine the concentrations of prostaglandins E2 and F2, (PGE2 and PGF2,) in the blood, testis and seminal plasma of mature male rainbow trout and in the ovarian fluid to assess the effects of these prostaglandins on sperm motility parameters when present in activation media. Also prolonged incubation with prostaglandins on sperm motility and calcium influx were studied. The profile of PGE2 and PGF2, differed in concentration between blood, testicular supernatant and seminal plasma. PGE2 was predominant in the blood sample (0.29 ng ml,1) and testicular supernatant (3.1 ng ml,1) whereas their level in seminal plasma was lower than PGF2, (0.23 ng ml,1). The concentrations of PGF2, in blood, testis and seminal plasma were 0.04, 0.99, 1.3 ng ml,1, respectively. In the ovarian fluid the concentrations of both prostaglandins were higher than in the male reproductive tract. Adding both prostaglandins to activation buffer (at concentrations 15 and 70 ng ml,1) had no effect on any CASA parameters. Calcium influx related to rainbow trout sperm incubations with PGE2, and PGF2, was not detected. After 24 h incubation of sperm in artificial seminal plasma solution without and with prostaglandins all sperm samples increased their motility potential and intracellular calcium concentration. Therefore, this effect was not related to the presence of prostaglandins. In summary PGE2, and PGF2, were present in the rainbow trout male reproductive tract, and their profile varies from that of blood, testis and seminal plasma. The specific role of both prostaglandins in salmonid sperm biology remains unclear. [source] Tunable transport of glucose through ionically-crosslinked alginate gels: Effect of alginate and calcium concentrationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Mari-Kate E. McEntee Abstract Alginate beads have numerous biomedical applications, ranging from cell encapsulation to drug release. The present study focuses on the controlled release of glucose from calcium-alginate beads. The effects of alginate concentrations (1,6 wt %) and calcium chloride concentrations (0.1,1.0M) on glucose release from beads were examined. It was found that the time required for complete glucose release from beads could be tuned from 15 min to over 2 h, simply by varying alginate and calcium chloride concentrations in beads. For calcium-alginate beads with sodium alginate concentrations of 1,4 wt %, higher sodium alginate concentrations lead to more prolonged release of glucose and thus a smaller value of a rate constant k, a parameter shown to be proportional to the diffusion coefficient of glucose in the alginate gel. For beads with sodium alginate concentrations of 4,6 wt %, there was no statistically significant difference in k values, indicating a lower limit for glucose release from calcium-alginate beads. Similarly, higher calcium chloride concentrations appear to extend glucose release, however, no conclusive trend can be drawn from the data. In a 50 : 50 mixture of calcium-alginate beads of two different alginate concentrations (1 and 4 wt %), glucose release showed a two-step profile over the time range of 20,50 min, indicating that the pattern and time of glucose release from beads can be tuned by making combinations of beads with varying alginate and/or calcium chloride concentrations. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] | ||||||||||||||||||||||||||||||||||||||||||||||