POLYMER COMPOSITES, Issue 8 2009
Vladimír Sedlarik
The structural and mechanical characteristics of polymeric biocomposites based on calcium lactate (CL) and either partially (88 mol%) or fully (98 mol%) hydrolyzed poly(vinyl alcohol) (PVA) were studied using optical microscopy, Fourier transform infrared spectroscopy equipped with attenuated total reflectance accessory, water content determination, and differential scanning calorimetry. In addition, the moisture absorption effect on the mechanical properties of the biocomposites was tested in this work. The results reveal that CL is a suitable modifier for both types of PVA. However, a more efficient enhancement of uniform shape and size distribution of CL particles within the PVA matrix was noticed in fully hydrolyzed matrix at low water contents. It is in agreement with glass transition temperature's observations. The samples conditioned at 50% of relative humidity (RH) showed decrease in E modulus and tensile strength in comparison with the material stored below 20% RH. Nevertheless, the enhancement of tensile properties, because of the modification with CL, was still noticeable especially for the partially hydrolyzed PVA-based biocomposites. The optimum concentration of the modifier was estimated on the basis of the obtained results. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source]

Electrical and thermal properties of nylon 6/calcium carbonate composites

ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2009
M. A. Moussa
Abstract Several polymer composites formed from nylon 6/CaCO3 with different ratios and particle sizes were prepared using modified and unmodified CaCO3 as inorganic filler. The modification of CaCO3 surfaces was carried out by adsorption of oleic acid from toluene. TGA and DSC measurements show that the glass transition temperatures reduced by the presence of inorganic filler, whereas the melting temperature did not influenced. In all prepared polymer composites, the presence of filler accelerates the degradation process of the polymer. Dielectric properties of the investigated samples were studied in the frequency range from 45 Hz to 1 MHz and at temperatures ranging between 50 and 200°C. The presence of CaCO3 led to a remarkable decrease in the conductivity of nylon 6. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 28:257,266, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20165 [source]

THE ROLE OF CALCIUM IN FLOW-STIMULATED BIOLUMINESCENCE OF THE RED TIDE DINOFLAGELLATE LINGULODINIUM POLYEDRUM

JOURNAL OF PHYCOLOGY, Issue 2000
P. Von Dassow
Many marine planktonic dinoflagellates emit flashes of light in response to either laminar or turbulent flows as well as direct mechanical stimulation. The production of a flash of light is known to be mediated by a proton-mediated action potential across the vacuolar membrane; the mechanotransduction process initiating this action potential is unknown. Here we report on an investigation into the role of Ca+2 in the mechanotransduction process regulating bioluminescence in the red tide dinoflagellate Lingulodinium polyedrum. Calcium ionophores and low concentrations of the membrane-disrupting agent digitonin stimulated bioluminescence only when calcium was present in the media or added with the agent, indicating that the flash-triggering vacuolar action potential is specifically stimulated by a calcium influx. A variety of known calcium channel blockers or antagonists inhibited mechanically stimulated bioluminescence but did not affect cellular bioluminescent capacity. In many cases the inhibitory affect occurred after only a brief exposure. In addition, gadolinium (Gd+3), a blocker of many stretch-activated ion channels, caused potent inhibition of mechanically stimulated bioluminescence. The order of potency of the transition metals tested was La+3 > Gd+3 > Co+2 > Mn+2 > Ni+2, similar to their potency as blockers of known calcium channels. Experiments with a quantified shear flow demonstrated that flow-stimulated bioluminescence depended on the level of extracellular calcium. Future work will elucidate the signaling pathway involving calcium-mediated flow-stimulated mechanotransduction. Our goal is to use bioluminescence as a proxy for the initial cellular mechanotransduction events triggered by fluid flow. [source]

RHEOLOGY OF DOUBLE (W/O/W) EMULSIONS PREPARED WITH SOYBEAN MILK AND FORTIFIED WITH CALCIUM

JOURNAL OF TEXTURE STUDIES, Issue 5 2010
ANDRÉS L. MÁRQUEZ
ABSTRACT The objective of this work was to study the rheological behavior of water-in-oil-in-water (w/o/w) emulsions prepared with soybean milk and sunflower oil, with different calcium solutions as the internal aqueous phase, in order to evaluate them as a vegetable substitute of whipped dairy cream. The obtained systems exhibited a creamy texture, which was attributed to the swelling of w/o droplets because of the osmotic gradient generated by the inclusion of soluble salts in the internal aqueous phase. A secondary factor could be the flocculation of w/o droplets due to the interaction of released calcium with soybean proteins at the interface. Consequently, the increase of calcium chloride content produced emulsions with higher consistency. A pasteurization produced flocculation and coalescence of w/o droplets only at high calcium chloride content. These double emulsions could be a potential alternative to the whipped dairy cream, because of their texture, reduced fat content and calcium contribution. PRACTICAL APPLICATIONS This article deals with the formulation of novel calcium-fortified food emulsions prepared with soybean milk and sunflower oil. Because calcium needs to be isolated from soybean milk components (proteins and phospholipids), we proposed to include calcium salts in the internal aqueous phase of a water-in-oil-in-water (w/o/w) emulsion. The practical applications of this research could include the formulation of low lipid content emulsions and the isolation of a component which is incompatible with the continuous aqueous phase. Particularly, this work leads to the understanding of how the inclusion of calcium salts in the internal aqueous phase of a w/o/w emulsion prepared with soybean milk affects the rheology and microstructure of the system. The results led to the conclusion that these emulsions can work as a whipped dairy cream substitute with vegetal components, low lipid content and important calcium contribution. [source]

GENES, CALCIUM AND MODIFYING FACTORS IN HYPERTROPHIC CARDIOMYOPATHY

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 1-2 2006
Tatiana Tsoutsman
SUMMARY 1Familial hypertrophic cardiomyopathy (FHC) is a primary disorder of the myocardium characterized by remarkable diversity in clinical presentations, ranging from no symptoms to severe heart failure and sudden cardiac death. 2Over the past 15 years, at least 11 genes have been identified, defects of which cause FHC. Most of these genes encode proteins that comprise the basic contractile unit of the heart (i.e. the sarcomere). 3Genetic studies are now beginning to have a major impact on the diagnosis in FHC, as well as in guiding treatment and preventative strategies. Although much is known about which genes cause disease, relatively little is known about the molecular steps leading from the gene defect to the clinical phenotype and what factors modify the expression of the mutant genes. 4Concurrent studies in cell culture and animal models of FHC are now beginning to shed light on the signalling pathways involved in FHC and the role of both environmental and genetic modifying factors. Calcium dysregulation appears to be important in the pathogenesis of FHC. 5Understanding these basic molecular mechanisms will ultimately improve our knowledge of the basic biology of heart muscle function and will therefore provide new avenues for diagnosis and treatment not only for FHC, but also for a range of human cardiovascular diseases. [source]

NANOMOLAR LEVEL OF OUABAIN INCREASES INTRACELLULAR CALCIUM TO PRODUCE NITRIC OXIDE IN RAT AORTIC ENDOTHELIAL CELLS

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 5-6 2004
Xian Hui Dong
Summary 1.,Changes in [Ca2+]i across the cell membrane and/or the sarcoplasmic reticulum regulate endothelial nitric oxide (NO) synthase activity. 2.,In the present study, we investigated the effect of ouabain, a specific inhibitor of Na+/K+ -ATPase, on NO release and [Ca2+]i movements in cultured rat aortic endothelial cells (RAEC) by monitoring NO production continuously using an NO-specific real-time sensor and by measuring the change in [Ca2+]i using a fluorescence microscopic imaging technique with high-speed wavelength switching. The t½ (half-time of the decline of [Ca2+]i to basal levels after stimulation with 10 µmol/L bradykinin) was used as an index of [Ca2+]i extrusion. 3.,A very low concentration of ouabain (10 nmol/L) did not increase the peak of NO production, but decreased the decay of NO release and, accordingly, increased integral NO production by the maximal dose,response concentration induced by bradykinin. The same dose of ouabain affected [Ca2+]i movements across the cell membrane and/or sarcoplasmic reticulum induced by bradykinin with a time-course similar to that of NO release. Moreover, the t½ was significantly increased. 4.,Pretreatment of RAEC with Na+ -free solution, an inhibitor of the Na+/Ca2+ exchanger, and nickel chloride hexahydrate prevented the effects induced by bradykinin and ouabain. 5.,These observations using real-time recording indicate that a small amount of ouabain contributes to the bradykinin-stimulated increase of NO production through inhibition of plasma membrane Na+/K+ -ATPase activity and an increase in intracellular Na+ concentrations. The membrane was then depolarized, leading to a decline in the bradykinin-stimulated increase in [Ca2+]i by forward mode Na+/Ca2+ exchange to prolong the Ca2+ signal time. 6.,From these results, we suggest that nanomolar levels of ouabain modulate [Ca2+]i movements and NO production in RAEC. [source]

Influence of citric acid on calcium sulfate dihydrate crystallization in aqueous media

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2007
S. Titiz-Sargut
Abstract The crystallization of Calcium sulfate dihydrate produced by the reaction between pure Ca(OH)2 suspension and H2SO4 solution was investigated at different pH values, temperatures and citric acid concentrations. Crystal size distributions, filtration rates and zeta potentials of gypsum were determined as a function of citric acid concentrations at pH 3.5 and 65°C. The influence of citric acid on the morphology of gypsum was also investigated and discussed. The average particle size of gypsum was reached to maximum in the presence of approximately 2500 ppm citric acid concentration, where the minimum cake resistance and maximum filtration rate were obtained. In the presence of citric acid, various crystal morphologies such as tabular, plate-like, double-taper leaf-like and flower-like, etc., were obtained. The change of morphology is related to the preferential adsorption of citric acid on different crystallographic faces. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Calcium handling in afferent arterioles

ACTA PHYSIOLOGICA, Issue 4 2004
M. Salomonsson
Abstract The cytosolic intracellular calcium concentration ([Ca2+]i) is a major determining factor in the vascular smooth muscle tone. In the afferent arteriole it has been shown that agonists utilizing G-protein coupled receptors recruit Ca2+ via release from intracellular stores and entry via pathways in the plasma membrane. The relative importances of entry vs. mobilization seem to differ between different agonists, species and preparations. The entry pathway might include different types of voltage sensitive Ca2+ channels located in the plasmalemma such as dihydropyridine sensitive L-type channels, T-type channels and P/Q channels. A role for non-voltage sensitive entry pathways has also been suggested. The importance of voltage sensitive Ca2+ channels in the control of the tone of the afferent arteriole (and thus in the control of renal function and whole body control of extracellular fluid volume and blood pressure) sheds light on the control of the membrane potential of afferent arteriolar smooth muscle cells. Thus, K+ and Cl, channels are of importance in their role as major determinants of membrane potential. Some studies suggest a role for calcium-activated chloride (ClCa) channels in the renal vasoconstriction elicited by agonists. Other investigators have found evidence for several types of K+ channels in the regulation of the afferent arteriolar tone. The available literature in this field regarding afferent arterioles is, however, relatively sparse and not conclusive. This review is an attempt to summarize the results obtained by others and ourselves in the field of agonist induced afferent arteriolar Ca2+ recruitment, with special emphasis on the control of voltage sensitive Ca2+ entry. Outline of the Manuscript: This manuscript is structured as follows: it begins with an introduction where the general role for [Ca2+]i as a key factor in the regulation of the tone of vascular smooth muscles (VSMC) is detailed. In this section there is an emphasis is on observations that could be attributed to afferent arteriolar function. We then investigate the literature and describe our results regarding the relative roles for Ca2+ entry and intracellular release in afferent arterioles in response to vasoactive agents, with the focus on noradrenalin (NA) and angiotensin II (Ang II). Finally, we examine the role of ion channels (i.e. K+ and Cl, channels) for the membrane potential, and thus activation of voltage sensitive Ca2+ channels. [source]

Anisotropic contraction in forisomes: Simple models won't fit

CYTOSKELETON, Issue 5 2008
Winfried S. Peters
Abstract Forisomes are ATP-independent, Ca2+ -driven contractile protein bodies acting as reversible valves in the phloem of plants of the legume family. Forisome contraction is anisotropic, as shrinkage in length is associated with radial expansion and vice versa. To test the hypothesis that changes in length and width are causally related, we monitored Ca2+ - and pH-dependent deformations in the exceptionally large forisomes of Canavalia gladiata by high-speed photography, and computed time-courses of derived geometric parameters (including volume and surface area). Soybean forisomes, which in the resting state resemble those of Canavalia geometrically but have less than 2% of the volume, were also studied to identify size effects. Calcium induced sixfold volume increases in forisomes of both species; in soybean, responses were completed in 0.15 s, compared to about 0.5 s required for a rapid response in Canavalia followed by slow swelling for several minutes. This size-dependent behavior supports the idea that forisome contractility might rest on similar mechanisms as those of polyelectrolyte gels, a class of artificial "smart" materials. In both species, time-courses of forisome length and diameter were variable and lacked correlation, arguing against a simple causal relationship between changes in length and width. Moreover, changes in the geometry of soybean forisomes differed qualitatively between Ca2+ - and pH-responses, suggesting that divalent cations and protons target different sites on the forisome proteins. Cell Motil. Cytoskeleton 2008. © 2008 Wiley-Liss, Inc. [source]

Changes in the potential quantum yield of photosystem II and the integrity of cell membranes relative to the elemental content of the epilithic desert lichen Ramalina maciformis

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2002
Jacob Garty
Abstract The present study used the epilithic fruticose lichen Ramalina maciformis to investigate the occurrence of mineral elements, including heavy metals, at a distance of up to 50 km from the industrial region in Ramat Hovav in the Negev Desert, Israel. The major objective of this study was an analytical comparison of elemental content and physiological parameters of lichen vitality, apart from a test of the applicability of this specific lichen in investigations of air pollution. The Ca, Cr, Cu, K, Mg, Na, Pb, S, Sr, and Zn content of thalli from the unpolluted Tellalim site collected in August 1997, transferred to 24 biomonitoring sites, and retrieved in April 1998 was analyzed in comparison with the following parameters: The potential quantum yield of photosystem II (PSII), and the integrity of cell membranes. Transplanted thalli in several sites at Ramat Hovav accumulated large amounts of most of the elements. The K content of the transplants located in the polluted sites indicated a leakage of this element, because this content was lower than that of thalli in unpolluted sites. Calcium, Cu, Mn, and Na showed an inverse correlation with the K content of the lichen. Calcium, Cu, and Sr showed an inverse correlation with the Fv/Fm ratio expressing the potential quantum yield of PSII. Calcium, Cr, Cu, Mg, Na, S, and Sr showed a positive correlation with the electrical conductivity corresponding with cell-membrane disintegration. The present study demonstrated a meaningful connection between enlarged concentrations of certain elements and physiological phenomena. The capability of the lichen to detect air pollution was found to be satisfactory. The dispersion of airborne heavy metals was found, however, to be local and limited to a few hundred meters from the source of pollution. [source]

Mono-, Di- and Polymeric Calcium and Gadolinium Complexes of the Tripodal Ligand 2,2,,2,,-Nitrilotribenzoic Acid

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2005
Stefan Wörl
Abstract Three novel carboxylate-bridged complexes incorporating the tripodal N,O ligand 2,2,,2,,-nitrilotribenzoic acid H3L of formula [CaII(H2L)(OH2)4][(H2L)]·4H2O (1), [CaII(OH2)4]-[CaII(L)(OH2)2]2·7H2O (2) and [GdIII(L)(OH2)3]2[GdIII(L)-(OH2)4]2·13H2O (3) were synthesized and characterized by X-ray crystallography. In all three complexes, the ligand H3L binds to the metal centre only by its three carboxylate donors, leaving the bridgehead nitrogen atom nonbonding. The calcium(II) ion in the monomeric complex 1 is distorted pentagonal-bipyramidal coordinated, the +1 charge of the complex cation [CaII(H2L)(OH2)4]+ is balanced by an H2L, anion and both units are connected by hydrogen bonds. The polymeric compound 2 displays a one-dimensional chain structure, in which two [CaII(L)]2, units form a dimeric structure and are connected by hydrated CaII ions. 3 contains two different [GdIII(L)(OH2)n] dimers. In one of them the two GdIII ions are linked by two monoatomic carboxylate O-bridges showing a short Gd···Gd distance of 3.99 Å. In the second, a syn - anti carboxylate 1,3-bridge with a longer Gd···Gd distance of 4.96 Å is observed. Magnetic measurements of 3 show paramagnetic behaviour with weak antiferromagnetic coupling. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Retina expresses a novel variant of the ryanodine receptor

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2007
Varda Shoshan-Barmatz
Abstract Calcium released from intracellular stores via the ryanodine receptor (RyR) mediates a variety of signalling processes. We previously showed that retina expresses the three known types of RyR, but retinal membrane preparations exhibit unique characteristics such as Ca2+ -independent [3H]ryanodine-binding and inhibition by caffeine. We have heretofore suggested that the major retinal RyR isoform is novel. The present study aimed to identify this receptor isoform and to localize RyR in mammalian retina. Immunoblotting with specific and pan-antibodies showed that the major retinal RyR has a mobility similar to that of RyR2 or RyR3. Real-time PCR revealed that the major type is RyR2, and RT-PCR followed by sequencing showed a transcript that encodes a protein with ~ 99% identity to RyR2, yet lacking two regions of seven and 12 amino acids and including an additional insertion of eight amino acids. An antibody against RyR2 localized this type to somas and primary dendrites of most retinal neurons. An antibody against RyR1 localized RyR to most somas but also revealed staining in photoreceptor outer segments, concentrated on the disk membranes at their rim. The ryanodine-binding properties and the electrophoretic mobility of RyR from the outer segments were similar to those of the whole retinal preparation. The results thus identify a novel variant of RyR2 which can contribute to regulating photoreceptor Ca2+ concentrations. The restricted localization of the outer segment RyR to the disk rim suggests that its activation mechanism involves a coupling between retinal RyR and the cGMP-gated channel. [source]

Plasma membrane Ca2+ -ATPase in the cilia of olfactory receptor neurons: possible role in Ca2+ clearance

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2007
Karen Castillo
Abstract Olfactory sensory neurons respond to odorants increasing Ca2+ concentrations in their chemosensory cilia. Calcium enters the cilia through cAMP-gated channels, activating Ca2+ -dependent chloride or potassium channels. Calcium also has a fundamental role in odour adaptation, regulating cAMP turnover rate and the affinity of the cyclic nucleotide-gated channels for cAMP. It has been shown that a Na+/Ca2+ exchanger (NCX) extrudes Ca2+ from the cilia. Here we confirm previous evidence that olfactory cilia also express plasma membrane Ca2+ -ATPase (PMCA), and show the first evidence supporting a role in Ca2+ removal. Both transporters were detected by immunoblot of purified olfactory cilia membranes. The pump was also revealed by immunocytochemistry and immunohistochemistry. Inside-out cilia membrane vesicles transported Ca2+ in an ATP-dependent fashion. PMCA activity was potentiated by luminal Ca2+ (K0.5 = 670 nm) and enhanced by calmodulin (CaM; K0.5 = 31 nm). Both carboxyeosin (CE) and calmidazolium reduced Ca2+ transport, as expected for a CaM-modulated PMCA. The relaxation time constant (,) of the Ca2+ -dependent Cl, current (272 ± 78 ms), indicative of luminal Ca2+ decline, was increased by CE (2181 ± 437 ms), by omitting ATP (666 ± 49 ms) and by raising pH (725 ± 65 ms), suggesting a role of the pump on Ca2+ clearance. Replacement of external Na+ by Li+ had a similar effect (, = 442 ± 8 ms), confirming the NCX involvement in Ca2+ extrusion. The evidence suggests that both Ca2+ transporters contribute to re-establish resting Ca2+ levels in the cilia following olfactory responses. [source]

Calcium,calmodulin-dependent protein kinase II phosphorylation modulates PSD-95 binding to NMDA receptors

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2006
Fabrizio Gardoni
Abstract At the postsynaptic membrane of excitatory synapses, NMDA-type receptors are bound to scaffolding and signalling proteins that regulate the strength of synaptic transmission. The cytosolic tails of the NR2A and NR2B subunits of NMDA receptor bind to calcium,calmodulin-dependent protein kinase II (CaMKII) and to members of the MAGUK family such as PSD-95. In particular, although NR2A and NR2B subunits are highly homologous, the sites of their interaction with CaMKII as well as the regulation of this binding differ. We identified PSD-95 phosphorylation as a molecular mechanism responsible for the dynamic regulation of the interaction of both PSD-95 and CaMKII with the NR2A subunit. CaMKII-dependent phosphorylation of PSD-95 occurs both in vitro, in GST-PSD-95 fusion proteins phosphorylated by purified active CaMKII, and in vivo, in transfected COS-7 as well as in cultured hippocampal neurons. We identified Ser73 as major phosphorylation site within the PDZ1 domain of PSD-95, as confirmed by point mutagenesis experiments and by using a phospho-specific antibody. PSD-95 Ser73 phosphorylation causes NR2A dissociation from PSD-95, while it does not interfere with NR2B binding to PSD-95. These results identify CaMKII-dependent phosphorylation of the PDZ1 domain of PSD-95 as a mechanism regulating the signalling transduction pathway downstream NMDA receptor. [source]

Calcium and Fos Involvement in Brain-Derived Ca2+ -Binding Protein (S100)-Dependent Apoptosis in Rat Phaeochromocytoma Cells

EXPERIMENTAL PHYSIOLOGY, Issue 3 2000
Stefania Fulle
Brain-derived calcium-binding protein S100 induces apoptosis in a significant fraction of rat phaeochromocytoma (PC12) cells. We used single cell techniques (patch clamp, videomicroscopy and immunocytochemistry) to clarify some of the specific aspects of S100-induced apoptosis, the modality(ies) of early intracellular Ca2+ concentration increase and the expression of some classes of genes (c-fos, c-jun, bax, bcl-x, p-15, p-21) known to be implicated in apoptosis of different cells. The results show that S100: (1) causes an increase of [Ca2+]i due to an increased conductance of L-type Ca2+ channels; (2) induces a sustained increase of the Fos levels which is evident since the first time point tested (3 h) and remains elevated until to the last time point (72 h). All these data suggest that S100-derived apoptosis in PC12 cells may be the consequence of a system involving an increase in L-type Ca2+ channel conductance with consequent [Ca2+]i increase which up-regulates, directly or indirectly, the expression of Fos. [source]

Calcium modulates endopeptidase 24.15 (EC 3.4.24.15) membrane association, secondary structure and substrate specificity

FEBS JOURNAL, Issue 12 2005
Vitor 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 tissues

FEBS JOURNAL, Issue 12 2003
Rui 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]

Biomineralization: Amorphous Calcium Carbonate is Stabilized in Confinement (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 13 2010
Mater.
F. C. Meldrum, H. K. Christenson, et al. describe on page 2108 a device based on two crossed cylinders used to study confinement effects on precipitation of calcium carbonate. Amorphous calcium carbonate (ACC) remains stable for days even when the confining surfaces are as far as a micrometer apart. Such stabilization of ACC in vitro may have important implications for the understanding of biomineralization. [source]

Amorphous Calcium Carbonate is Stabilized in Confinement

ADVANCED FUNCTIONAL MATERIALS, Issue 13 2010
Christopher J. Stephens
Abstract Biominerals typically form within localized volumes, affording organisms great control over the mineralization process. The influence of such confinement on crystallization is studied here by precipitating CaCO3 within the confines of an annular wedge, formed around the contact point of two crossed half-cylinders. The cylinders are functionalized with self-assembled monolayers of mercaptohexadecanoic acid on gold. This configuration enables a systematic study of the effects of confinement since the surface separation increases continuously from zero at the contact point to macroscopic (mm) separations. While oriented rhombohedral calcite crystals form at large (>10,µm) separations, particles with irregular morphologies and partial crystallinity are observed as the surface separation approaches the dimensions of the unconfined crystals (5,10,µm). Further increase in the confinement has a significant effect on the crystallization process with flattened amorphous CaCO3 (ACC) particles being formed at micrometer separations. These ACC particles show remarkable stability when maintained within the wedge but rapidly crystallize on separation of the cylinders. A comparison of bulk and surface free-energy terms shows that ACC cannot be thermodynamically stable at these large separations, and the stability is attributed to kinetic factors. This study therefore shows that the environment in which minerals form can have a significant effect on their stability and demonstrates that ACC can be stabilized with respect to the crystalline polymorphs of CaCO3 by confinement alone. That ACC was stabilized at such large (micrometer) separations is striking, and demonstrates the versatility of this strategy, and its potential value in biological systems. [source]

Calcium and magnesium competitively influence the growth of a PMR1 deficient Saccharomyces cerevisiae strain

FEMS MICROBIOLOGY LETTERS, Issue 2 2005
Réka Szigeti
Abstract PMR1, the Ca2+/Mn2+ ATPase of the secretory pathway in Saccharomyces cerevisiae was the first member of the secretory pathway Ca2+ ATPases (SPCA) to be characterized. In the past few years, pmr1, yeast have received more attention due to the recognition that the human homologue of this protein, hSPCA1 is defective in chronic benign pemphigus or Hailey,Hailey disease (HHD). Recent publications have described pmr1, S. cerevisiae as a useful model organism for studying the molecular pathology of HHD. Some observations indicated that the high Ca2+ sensitive phenotype of PMR1 defective yeast strains may be the most relevant in this respect. Here we show that the total cellular calcium response of a pmr1, S. cerevisiae upon extracellular Ca2+ challenge is decreased compared to the wild type strain similarly as observed in keratinocytes. Additionally, the novel magnesium sensitivity of PMR1 defective yeast is revealed, which appears to be a result of competition for uptake between Ca2+ and Mg2+ at the plasma membrane level. Our findings indicate that extracellular Ca2+ and Mg2+ competitively influence the intracellular Ca2+ homeostasis of S. cerevisiae. These observations may further our understanding of HHD. [source]

Distribution of benthic diatoms in U.S. rivers in relation to conductivity and ionic composition

FRESHWATER BIOLOGY, Issue 8 2003
Marina Potapova
Summary 1We quantified the relationships between diatom relative abundance and water conductivity and ionic composition, using a dataset of 3239 benthic diatom samples collected from 1109 river sites throughout the U.S.A. [U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program dataset]. This dataset provided a unique opportunity to explore the autecology of freshwater diatoms over a broad range of environmental conditions. 2Conductivity ranged from 10 to 14 500 ,S cm,1, but most of the rivers had moderate conductivity (interquartile range 180,618 ,S cm,1). Calcium and bicarbonate were the dominant ions. Ionic composition, however, varied greatly because of the influence of natural and anthropogenic factors. 3Canonical correspondence analysis (CCA) and Monte Carlo permutation tests showed that conductivity and abundances of major ions (HCO + CO, Cl,, SO, Ca2+, Mg2+, Na+, K+) all explained a statistically significant amount of the variation in assemblage composition of benthic diatoms. Concentrations of HCO + CO and Ca2+ were the most significant sources of environmental variance. 4The CCA showed that the gradient of ionic composition explaining most variation in diatom assemblage structure ranged from waters dominated by Ca2+ and HCO + CO to waters with higher proportions of Na+, K+, and Cl,. The CCA also revealed that the distributions of some diatoms correlated strongly with proportions of individual cations and anions, and with the ratio of monovalent to divalent cations. 5We present species indicator values (optima) for conductivity, major ions and proportions of those ions. We also identify diatom taxa characteristic of specific major-ion chemistries. These species optima may be useful in future interpretations of diatom ecology and as indicator values in water-quality assessment. [source]

Temporal coherence of two alpine lake basins of the Colorado Front Range, U.S.A.

FRESHWATER BIOLOGY, Issue 3 2000
J. I. L. L. S. Baron
1. Knowledge of synchrony in trends is important to determining regional responses of lakes to disturbances such as atmospheric deposition and climate change. We explored the temporal coherence of physical and chemical characteristics of two series of mostly alpine lakes in nearby basins of the Colorado Rocky Mountains. Using year-to-year variation over a 10-year period, we asked whether lakes more similar in exposure to the atmosphere be-haved more similarly than those with greater influence of catchment or in-lake processes. 2. The Green Lakes Valley and Loch Vale Watershed are steeply incised basins with strong altitudinal gradients. There are glaciers at the heads of each catchment. The eight lakes studied are small, shallow and typically ice-covered for more than half the year. Snowmelt is the dominant hydrological event each year, flushing about 70% of the annual discharge from each lake between April and mid-July. The lakes do not thermally stratify during the period of open water. Data from these lakes included surface water temper-ature, sulphate, nitrate, calcium, silica, bicarbonate alkalinity and conductivity. 3. Coherence was estimated by Pearson's correlation coefficient between lake pairs for each of the different variables. Despite close geographical proximity, there was not a strong direct signal from climatic or atmospheric conditions across all lakes in the study. Individual lake characteristics overwhelmed regional responses. Temporal coherence was higher for lakes within each basin than between basins and was highest for nearest neighbours. 4. Among the Green Lakes, conductivity, alkalinity and temperature were temporally coherent, suggesting that these lakes were sensitive to climate fluctuations. Water tem-perature is indicative of air temperature, and conductivity and alkalinity concentrations are indicative of dilution from the amount of precipitation flushed through by snowmelt. 5. In Loch Vale, calcium, conductivity, nitrate, sulphate and alkalinity were temporally coherent, while silica and temperature were not. This suggests that external influences are attenuated by internal catchment and lake processes in Loch Vale lakes. Calcium and sulphate are primarily weathering products, but sulphate derives both from deposition and from mineral weathering. Different proportions of snowmelt versus groundwater in different years could influence summer lake concentrations. Nitrate is elevated in lake waters from atmospheric deposition, but the internal dynamics of nitrate and silica may be controlled by lake food webs. Temperature is attenuated by inconsistently different climates across altitude and glacial meltwaters. 6. It appears that, while the lakes in the two basins are topographically close, geologically and morphologically similar, and often connected by streams, only some attributes are temporally coherent. Catchment and in-lake processes influenced temporal patterns, especially for temperature, alkalinity and silica. Montane lakes with high altitudinal gradients may be particularly prone to local controls compared to systems where coherence is more obvious. [source]

Are environmental conditions recorded by the organic matrices associated with precipitated calcium carbonate in cyanobacterial microbialites?

GEOBIOLOGY, Issue 2 2006
P. GAUTRET
ABSTRACT The amino acid composition of organic matrices associated with calcium carbonate precipitates in microbialites built by different Phormidium species (cyanobacteria) has been compared for samples recovered in lagoonal settings from two regions of the Southern Tropical Pacific separated by more than 4000 km: New Caledonia (Nouméa lagoon) and French Polynesia (Tikehau atoll). Calcium carbonate precipitation in these microbial structures was observed mainly in the interior of the domes and clearly separated from the photosynthetically active surface layer. This study focuses on the hydrolysable amino acid composition of the associated organic matrices that are typically rich in cysteine, leucine, alanine and arginine in New Caledonia, whereas they are particularly rich in dicarboxylic amino acids in French Polynesia. This striking difference is seemingly related to different environmental conditions that characterize the two reef settings. The high cysteine content suggests an origin from metallothioneins produced by the cyanobacteria and/or by epiphytic diatoms that were observed on the top layer, as the result of the input of metals from terrestrial origin in the Nouméa lagoon. In addition, we analysed the bulk organic matter of the photosynthetically active surface layer and of the interior of the domes. The former showed remarkable variations of amino acid composition throughout the year 2001, which may potentially reflect the impact of climatological events (e.g. cyclones) and/or a much stronger seasonality in New Caledonia than in French Polynesia. Although the mechanisms behind the differences remain elusive, our study clearly shows that environmental conditions can be reflected by amino acid compositions, particularly for the organic matrices associated with carbonate precipitates. [source]

Calcium signaling in invertebrate glial cells

GLIA, Issue 7 2006
Christian Lohr
Abstract Calcium signaling studies in invertebrate glial cells have been performed mainly in the nervous systems of the medicinal leech (Hirudo medicinalis) and the sphinx moth Manduca sexta. The main advantages of studing glial cells in invertebrate nervous systems are the large size of invertebrate glial cells and their easy accessibility for optical and electrophysiological recordings. Glial cells in both insects and annelids express voltage-gated calcium channels and, in the case of leech glial cells, calcium-permeable neurotransmitter receptors, which allow calcium influx as one major source for cytosolic calcium transients. Calcium release from intracellular stores can be induced by metabotropic receptor activation in leech glial cells, but appears to play a minor role in calcium signaling. In glial cells of the antennal lobe of Manduca, voltage-gated calcium signaling changes during postembryonic development and is essential for the migration of the glial cells, a key step in axon guidance and in stabilization of the glomerular structures that are characteristic of primary olfactory centers. © 2006 Wiley-Liss, Inc. [source]

Calcium signaling in specialized glial cells,

GLIA, Issue 7 2006
Monica R. Metea
Abstract This article reviews calcium signaling in three specialized types of glial cells: Müller cells of the retina, Bergmann glial cells of the cerebellum, and radial glial cells of the developing cortex. Müller cells generate spontaneous and neuronal activity-evoked increases in Ca2+. Neuron to Müller cell signaling is mediated by neuronal release of ATP and activation of glial P2Y receptors. Müller cells, in turn, modulate neuronal excitability and mediate vasomotor responses. Bergmann glial cells also generate spontaneous and activity-evoked Ca2+ increases. Neuron to Bergmann glia signaling is mediated by neuronal release of nitric oxide, noradrenaline, and glutamate. In Bergmann glia, Ca2+ increases control the structural and functional interactions between these cells and Purkinje cell synapses. In the ventricular zone of the developing cortex, radial glial cells generate spontaneous Ca2+ increases that propagate as Ca2+ waves through clusters of neighboring glial cells. These Ca2+ increases control cell proliferation and neurogenesis. © 2006 Wiley-Liss, Inc. [source]

Structural Characterization of the Transient Amorphous Calcium Carbonate Precursor Phase in Sea Urchin Embryos,

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2006
Y. Politi
Abstract Sea urchin embryos form their calcitic spicular skeletons via a transient precursor phase composed of amorphous calcium carbonate (ACC). Transition of ACC to calcite in whole larvae and isolated spicules during development has been monitored using X-ray absorption spectroscopy (XAS). Remarkably, the changing nature of the mineral phase can clearly be monitored in the whole embryo samples. More detailed analyses of isolated spicules at different stages of development using both XAS and infrared spectroscopy demonstrate that the short-range order of the transient ACC phase resembles calcite, even though infrared spectra show that the spicules are mostly composed of an amorphous mineral phase. The coordination sphere is at first distorted but soon adopts the octahedral symmetry typical of calcite. Long-range lattice rearrangement follows to form the calcite single crystal of the mature spicule. These studies demonstrate the feasibility of real-time monitoring of mineralized-tissue development using XAS, including the structural characterization of transient amorphous phases at the atomic level. [source]

Cytosolic calcium regulates liver regeneration in the rat,

HEPATOLOGY, Issue 2 2010
Laura Lagoudakis
Liver regeneration is regulated by growth factors, cytokines, and other endocrine and metabolic factors. Calcium is important for cell division, but its role in liver regeneration is not known. The purpose of this study was to understand the effects of cytosolic calcium signals in liver growth after partial hepatectomy (PH). The gene encoding the calcium-binding protein parvalbumin (PV) targeted to the cytosol using a nuclear export sequence (NES), and using a discosoma red fluorescent protein (DsR) marker, was transfected into rat livers by injecting it, in recombinant adenovirus (Ad), into the portal vein. We performed two-thirds PH 4 days after Ad-PV-NES-DsR or Ad-DsR injection, and liver regeneration was analyzed. Calcium signals were analyzed with fura-2-acetoxymethyl ester in hepatocytes isolated from Ad-infected rats and in Ad-infected Hela cells. Also, isolated hepatocytes were infected with Ad-DsR or Ad-PV-NES-DsR and assayed for bromodeoxyuridine incorporation. Ad-PV-NES-DsR injection resulted in PV expression in the hepatocyte cytosol. Agonist-induced cytosolic calcium oscillations were attenuated in both PV-NES,expressing Hela cells and hepatocytes, as compared to DsR-expressing cells. Bromodeoxyuridine incorporation (S phase), phosphorylated histone 3 immunostaining (mitosis), and liver mass restoration after PH were all significantly delayed in PV-NES rats. Reduced cyclin expression and retinoblastoma protein phosphorylation confirmed this observation. PV-NES rats exhibited reduced c-fos induction and delayed extracellular signal-regulated kinase 1/2 phosphorylation after PH. Finally, primary PV-NES,expressing hepatocytes exhibited less proliferation and agonist-induced cyclic adenosine monophosphate responsive element binding and extracellular signal-regulated kinase 1/2 phosphorylation, as compared with control cells. Conclusion: Cytosolic calcium signals promote liver regeneration by enhancing progression of hepatocytes through the cell cycle. (HEPATOLOGY 2010;) [source]

Corticosterone shifts different forms of synaptic potentiation in opposite directions

HIPPOCAMPUS, Issue 6 2005
Harm J. Krugers
Abstract Calcium entering the cell via different routes, e.g.,N -methyl- D -aspartate (NMDA) receptors or voltage-dependent calcium channels (VDCCs), plays a pivotal role in hippocampal synaptic potentiation. Since corticosteroid hormones have been reported to enhance calcium influx through VDCCs, one may predict that these hormones facilitate hippocampal synaptic efficacy. Surprisingly, though, stress and corticosteroids have so far been found to reduce synaptic potentiation. Here, we addressed this apparent paradox and examined synaptic potentiation in the CA1 area of hippocampal slices from mice with low basal corticosterone levels 1,4 h after a brief in vitro administration of corticosterone. Nifedipine and APV were used to isolate NMDA receptor-mediated and VDCC-mediated long-term potentiations (LTPs), respectively. We report that corticosterone facilitates synaptic potentiation that depends on activation of VDCCs while impairing synaptic plasticity that is mediated by NMDA receptor activation. The glucocorticoid-receptor (GR) antagonist RU 38486 blocked both the effects of corticosterone. These results indicate that the net effect of corticosteroid hormones on synaptic plasticity is determined by the balance between different types of potentiation, a balance that may be region specific and depends on the experimental conditions. We speculate that these opposite effects on synaptic efficacy are involved in the bidirectional modulation of cognitive performance by corticosteroid hormones. © 2005 Wiley-Liss, Inc. [source]

Calcium supplementation of breeding birds: directions for future research

IBIS, Issue 4 2004
S. James Reynolds
Calcium is an essential nutrient for avian reproduction. Calcium-rich foods are consumed by breeding birds for production of eggshells and for provisioning chicks that are mineralizing skeletal tissues. A number of studies have documented calcium-limited reproduction, and calcium supplementation has been employed over the last decade to demonstrate degrees, causes and consequences of calcium limitation. However, supplementation studies have produced equivocal findings resulting from an absence of calcium limitation in the study species, a poorly designed supplementation procedure or both. Prior to effective calcium supplementation, many factors need to be considered. Calcium-limited breeding in birds can only be detected by monitoring breeding attempts for more than one year and by ensuring that the measured breeding parameters are sensitive to calcium availability. Natural calcium availability needs to be estimated, and daily calcium budgets for the appropriate reproductive stages determined for the study species. Most crucially, if calcium limitation of breeding is caused by secondary calcium limitation (e.g. through heavy metal toxicity), calcium supplementation will probably be ineffective. Effective calcium supplementation will then be achieved through careful planning , a study over several years using appropriate supplements (i.e. naturally occurring ones used by breeding birds), applied at the appropriate time of year (i.e. prelaying and/or chick-rearing phases) and using a response variable that is highly sensitive to calcium availability. If properly planned and performed, calcium supplementation is a cost-effective and potent tool for the study of bird breeding biology. [source]

Lack of desquamation , the Achilles heel of the reconstructed epidermis

INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 5 2002
M. Ponec
Synopsis The use of human skin equivalents for screening tests aiming to assess repetitive application of various test agents is hampered by the lack of desquamation in vitro. The present study was undertaken to examine whether the desquamation can be induced by various treatments including mechanical stress, application of various agents that should decrease the surface pH and calcium level, activate the enzymes involved in desquamation process or UV irradiation. In addition, the effect of ,-hydroxyacids, known to enhance desquamation and to improve the stratum corneum barrier function in vivo, was examined as well. Human epidermis reconstructed on de-epidermized dermis or on fibroblast-populated collagen matrices during a 2-week culture at the air,liquid interface underwent various treatments during an additional 3-week period. The effects of treatments were evaluated on the basis of tissue morphology and lipid composition. The results of the present study revealed that cell shedding could only be induced by a mild repetitive mechanical treatment. The lack of desquamation, under most in vitro conditions, has a practical consequence, since it may hamper the use of reconstructed epidermis for various screening studies aiming to examine the repetitive exposure to topical agents or UV irradiation. The gradual thickening of the stratum corneum will lead to its higher resistance to the environmental stimuli and in this way affect the outcome of the tests. Furthermore, from the results obtained in the present study, it became evident that one should be careful in selecting endpoints when, for example, the effects of agents known to modulate melanogenesis are examined. Résumé L'utilization d'équivalents cutanés humains dans les procédures de criblage, afin d'estimer l'action répétée de divers agents, est entravée par l'absence de desquamation in vitro. La présente étude a été entreprise afin de déterminer dans quelle mesure la desquamation peut être induite par différents traitements tels que stress mécanique, application d'agents divers qui conduiraient à une chute du pH de surface et du taux de Calcium, activeraient les enzymes impliquées dans le processus de desquamation, ou l'irradiation UV. De plus, l'effet des , hydroxy-acides, connus pour favouriser la desquamation et d'améliorer la fonction barrière du Stratum-Corneum in vivo, a étéétudié. L'épiderme humain reconstruit sur un derme dé-épidermisé ou sur des matrices de collagène colonisées par des fibroblastes pendant 2 semaines de culture, en interface air × liquide, a subi divers traitements pendant une période additionnelle de 3 semaines. Les effets de ces traitements étaient évalués sur des critères morphologiques du tissu ainsi que la composition en lipides. Les résultats de cette étude montrent que l'élimination cellulaire ne peut être induite que par un léger traitement mécanique répété. L'absence de desquamation dans la plupart des conditions in vitro a une conséquence pratique puisqu'elle peut entraver l'utilization de l'épiderme reconstruit à des fins diverses de criblage en vue d'appréhender les expositions répétées à des agents topiques, ou l'irradiation UV. L'épaississement progressif du Stratum-Corneum lui confèrera une résistance accrue aux stimuli environnementaux qui, en retour, modifiera les résultats des tests. De plus, les résultats de cette présente étude impliquent à l'évidence une précaution dans la sélection des cinétiques de mesures lorsque, par exemple, les effets des agents connus pour moduler la mélanogénèse sont étudiés. [source]