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Ca2+ Clearance (ca2+ + clearance)
Selected AbstractsPlasma membrane Ca2+ -ATPase in the cilia of olfactory receptor neurons: possible role in Ca2+ clearanceEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2007Karen 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] Transient rise in intracellular calcium produces a long-lasting increase in plasma membrane calcium pump activity in rat sensory neuronsJOURNAL OF NEUROCHEMISTRY, Issue 4 2002William J. Pottorf II Abstract The plasma membrane Ca2+ ATPase (PMCA) plays a major role in clearing Ca2+ from the neuronal cytoplasm. Calmodulin stimulates PMCA activity and for some isoforms this activation persists following clearance of Ca2+ owing to the slow dissociation of calmodulin. We tested the hypothesis that PMCA-mediated Ca2+ efflux from rat dorsal root ganglion (DRG) neurons in culture would remain stimulated following increases in intracellular Ca2+ concentration ([Ca2+]i). PMCA-mediated Ca2+ extrusion was recorded following brief trains of action potentials using indo-1-based photometry in the presence of cyclopiazonic acid. A priming stimulus that increased [Ca2+]i to 506 ± 28 nm (>15 min) increased the rate constant for [Ca2+]i recovery by 47 ± 3%. Ca2+ clearance from subsequent test stimuli remained accelerated for up to an hour despite removal of the priming stimulus and a return to basal [Ca2+]i. The acceleration depended on the magnitude and duration of the priming [Ca2+]i increase, but was independent of the source of Ca2+. Increases in [Ca2+]i evoked by prolonged depolarization, sustained trains of action potentials or activation of vanilloid receptors all accelerated Ca2+ efflux. We conclude that PMCA-mediated Ca2+ efflux in DRG neurons is a dynamic process in which intense stimuli prime the pump for the next Ca2+ challenge. [source] Ca2+ -dependent inactivation of Ca2+ -induced Ca2+ release in bullfrog sympathetic neuronsTHE JOURNAL OF PHYSIOLOGY, Issue 14 2008Tenpei Akita We studied inactivation of Ca2+ -induced Ca2+ release (CICR) via ryanodine receptors (RyRs) in bullfrog sympathetic neurons. The rate of rise in [Ca2+]i due to CICR evoked by a depolarizing pulse decreased markedly within 10,20 ms to a much slower rate despite persistent Ca2+ entry and little depletion of Ca2+ stores. The Ca2+ entry elicited by the subsequent pulse within 50 ms, during which the [Ca2+]i level remained unchanged, did not generate a distinct [Ca2+]i rise. This mode of [Ca2+]i rise was unaffected by a mitochondrial uncoupler, carbonyl cyanide p -trifluromethoxy-phenylhydrazone (FCCP, 1 ,m). Paired pulses of varying interval and duration revealed that recovery from inactivation became distinct , 50 ms after depolarization and depended on [Ca2+]i. The inactivation was prevented by BAPTA (, 100 ,m) but not by EGTA (, 10 mm), whereas the activation was less affected by BAPTA. When CICR was partially activated, some of the non-activated RyRs were also inactivated directly. Thus, the inactivation in these neurons is induced by Ca2+ binding to the high-affinity regulatory sites residing very close to Ca2+ channels and/or RyRs, although the sites for activation are located much closer to those Ca2+ sources. The rate of [Ca2+]i decay after the pulse decreased with increasing pulse duration longer than 10 ms, and this was abolished by BAPTA. Thus, some mechanism counteracting Ca2+ clearance is induced after full inactivation and potentiated during the pulse. Possible models for RyR inactivation were proposed and the roles of inactivation in Ca2+ signalling were discussed. [source] | ||||||||||