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High Ca2+ (high + ca2+)
Selected AbstractsRelationship between boron and calcium in the N2 -fixing legume,rhizobia symbiosisPLANT CELL & ENVIRONMENT, Issue 11 2003M. REDONDO-NIETO ABSTRACT Because boron (B) and calcium (Ca2+) seem to have a strong effect on legume nodulation and nitrogen fixation, rhizobial symbiosis with leguminous plants, grown under varying concentrations of both nutrients, was investigated. The study of early pre-infection events included the capacity of root exudates to induce nod genes, and the degree of adsorption of bacteria to the root surface. Both phenomena were inhibited by B deficiency, and increased by addition of Ca2+, resulting in an increase of the number of nodules. The infection and invasion steps were investigated by fluorescence microscopy in pea nodules harbouring a Rhizobium leguminosarum strain that constitutively expresses green fluorescent protein. High Ca2+ enhanced cell and tissue invasion by Rhizobium, which was highly inhibited after B deficiency. This was combined with an increased B concentration in nodules of plants grown on B-free medium and supplemented with high Ca2+ concentrations, and that can be attributed to an increased B import to the nodules. Histological examination of indeterminate (pea) and determinate (bean) nodules showed an altered nodule anatomy at low B content of the tissue. The moderate increase in nodular B due to additional Ca2+ was not sufficient to prevent the abnormal cell wall structure and the aberrant distribution of pectin polysaccharides in B-deficient treatments. Overall results indicate that the development of the symbiosis depends of the concentration of B and Ca2+, and that both nutrients are essential for nodule structure and function. [source] Mechanisms of ATP action on motor nerve terminals at the frog neuromuscular junctionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2005S. Grishin Abstract We have shown previously that ATP inhibits transmitter release at the neuromuscular junction through the action on metabotropic P2Y receptors coupled to specific second messenger cascades. In the present study we recorded K+ or Ca2+ currents in motor nerve endings or blocked K+ or Ca2+ channels in order to explore the nature of downstream presynaptic effectors. Endplate currents were presynaptically depressed by ATP. Blockers of Ca2+ -activated K+ -channels, such as iberiotoxin, apamin or tetraethylammonium, did not change the depressant action of ATP. By contrast, K+ channel blocker 4-aminopyridine (4-AP) and raised extracellular Ca2+ attenuated the effect of ATP. However, these effects of 4-AP and high Ca2+ were reversed by Mg2+, suggesting Ca2+ -dependence of the ATP action. Ba2+ promoted the depressant action of ATP as did glibenclamide, a blocker of ATP-sensitive K+ channels, or mild depolarization produced by 7.5 mm K+. None of the K+ channel blockers affected the depressant action of adenosine. Focal recording revealed that neither ATP nor adenosine affected the fast K+ currents of the motor nerve endings. However, unlike adenosine, ATP or UTP, an agonist of P2Y receptors, reversibly reduced the presynaptic Ca2+ -current. This effect was abolished by suramin, an antagonist of P2 receptors. Depressant effect of ATP on the endplate and Ca2+ -currents was mimicked by arachidonate, which precluded the action of ATP. ATP reduced acetylcholine release triggered by ionomycin or sucrose, suggesting inhibition of release machinery. Thus, the presynaptic depressant action of ATP is mediated by inhibition of Ca2+ channels and by mechanism acting downstream of Ca2+ entry. [source] Electrophysiological characterization of laminar synaptic inputs to the olfactory tubercle of the rat studied in vitro: modulation of glutamatergic transmission by cholinergic agents is pathway-specificEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2001G. S. Owen Abstract We have exploited the complementary arrangement of afferents in a coronal slice (300,400 µm) of the rat olfactory tubercle (OT) maintained in vitro to investigate transmission in two separate synaptic pathways. We recorded extracellular responses within the OT dense cell layer in slices and stimulated either the outermost layer to activate primary olfactory fibres or deeper to activate secondary input. Superficial stimulation produced a synaptic potential with superimposed population spike. This interpretation was based on blockade by calcium removal from the bathing medium and the use of the glutamate antagonist DNQX (10 µm); the spike was found to be selectively suppressed by tetrodotoxin applied near the cells. The spike, but not the synaptic wave, was depressed by 12 mm Ca2+ and enhanced by 1 mm Ba2+ in the bathing medium. Deep stimulation to activate association and intrinsic fibres elicited a nerve volley followed by a later response, also blocked by Ca2+ removal or 10 µm DNQX. It was unaffected by high Ca2+ or Ba2+, hence resulting from synaptic and not action current flow. Removal of Mg2+ from the bathing medium revealed an NMDA component of synaptic transmission at both loci that was selectively blocked by D-AP-5. The deep synaptic response, only, was depressed by carbachol IC50 7 µm or muscarine IC50 13 µm. This depression was also induced by AChE inhibitors eserine or tacrine and was antagonized by 1 µm atropine or 5,10 µm clozapine. These results characterize transmission in the OT and demonstrate a role for muscarinic modulation of deeper synapses in the OT that is influenced by psychotherapeutic drugs. [source] Ecological gradients, subdivisions and terminology of north-west European miresJOURNAL OF ECOLOGY, Issue 2 2000B. D. Wheeler Summary 1,The historical development of mire ecology and terminology is reviewed in relation to evolving concepts and perceptions, and the diverse schools and traditions of vegetation and habitat description and research. 2,Most ecological and floristic variation within north-west European mire vegetation is accounted for by three ecological gradients: the acid base-poor vs. neutral, base- and bicarbonate-rich gradient; the gradient in fertility related to availability of the limiting nutrient elements N and P; and the water level gradient. Effects of salinity and the spring,flush,fen gradients are of more local significance, usually easily recognized. Land use is an important additional factor. 3,The mineral-soil-water limit between ombrotrophic and minerotrophically influenced sites is not sharp, and cannot be related to consistent differences in either vegetation or water chemistry. It should be abandoned as a general main division within mires. 4,The most important natural division is between ,bog', with pH generally < 5.0, low Ca2+, and Cl, and SO42, as the main inorganic anions, typically dominated by sphagna, ericoids and calcifuge Cyperaceae, and ,fen', with pH generally > 6.0, high Ca2+ and HCO3,, vegetation rich in dicotyledonous herbs and ,brown mosses'. This division is reflected in a bimodal distribution of pH. 5,The terms oligotrophic, mesotrophic and eutrophic should refer only to nutrient richness (fertility, mainly N and P), not to base richness (metallic cations and pH). 6,It is recommended that ,mire' should embrace both wetlands on peat and related communities on mineral soils, that ,bog' (unqualified) should encompass both ombrotrophic and weakly minerotrophic mires, including ,bog woodland', and that ,fen' should be restricted to base-rich mires but include both herbaceous and wooded vegetation (,fen carr'). 7,Definitions are given for a range of broadly defined categories that should cover most vegetation types commonly encountered. The relation of these to British national vegetation classification types and to major units in European phytosociology is outlined. [source] CREATINE KINASE INHIBITOR IODOACETAMIDE ANTAGONIZES CALCIUM-STIMULATED INOTROPY IN CARDIOMYOCYTESCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 2 2009Jun Ren SUMMARY 1Inhibition of creatine kinase is known to suppress cardiac contractile reserve in intact hearts, although the underlying mechanism has not been elucidated. 2The present study was designed to examine whether cardiac depression induced by creatine kinase inhibition was due to action at the level of the essential contractile element, namely cardiomyocytes. Adult rat cardiomyocytes were perfused with the creatine kinase inhibitor iodoacetamide (90 µmol/L) for 90 min. Mechanical and intracellular Ca2+ properties were evaluated using edge-detection and fluorescence microscopy, respectively. Myocytes were superfused with normal (1.3 mmol/L) or high (3.3 mmol/L) extracellular Ca2+ contractile buffer. Mechanical function was examined, including peak shortening (PS), maximal velocity of shortening/relengthening (±dL/dt), time to 90% PS (TPS90), time to 90% relengthening (TR90) and integration of shortening/relengthening (normalized to PS). Intracellular Ca2+ transients were evaluated using the following indices: resting and rise of fura-2 fluorescence intensity (,FFI) and intracellular Ca2+ decay time constant. 3The results indicate that elevated extracellular Ca2+ stimulated cardiomyocyte positive inotrope, manifested as increased PS, ±dL/dt, area of shortening, resting FFI and ,FFI associated with a shortened TR90 and intracellular Ca2+ decay time constant. High extracellular Ca2+ did not affect TPS90 and area of relengthening. Iodoacetamide ablated high Ca2+ -induced increases in PS, ±dL/dt, area of shortening, resting FFI, ,FFI and shortened TR90 and intracellular Ca2+ decay time constant. Iodoacetamide itself significantly enhanced the area of relengthening and TR90 without affecting other indices. 4Collectively, these data demonstrate that inhibition of creatine kinase blunts high extracellular Ca2+ -induced increases in cardiomyocyte contractile response (i.e. cardiac contractile reserve). [source] | ||||||||||