title: Sodium-calcium exchange affects local calcium signal decay and the rate of exocytotic secretion in single chromaffin cells.
abstract: The effects of Na+ deprivation on local calcium signal decay and the rate of exocytotic secretion were measured in single bovine chromaffin cells to determine whether Na-Ca exchange influences the local cytosolic Ca2+ signal for neurohormone release. Na+ replacement with N-methylglucamine caused a marked slowing of the decay of the local Ca2+ signal near points of its initiation, as measured by high-resolution fluorescent Ca2+ imaging in the confocal laser scanning microscope. Na+ replacement also resulted in a doubling of the rate and magnitude of exocytotic secretion measured in single cells by high-resolution microamperometry. Release rates provide an independent measure of local active zone Ca2+. Five repetitive stimulations of the same cell in Na+-free, but not in Na+-containing, medium resulted in a progressively increasing rate of catecholamine release, suggesting an increasing level of active zone Ca2+ and a role of Na-Ca exchange activity in Ca2+ clearance between stimulations. As secretory activity and its triggering Ca2+ signals are known to be co-localized in active zones along the plasma membrane, the results suggest that Na-Ca exchange may influence the decay of the local Ca2+ signal for exocytotic secretion. This would be consistent with a contribution to local Ca2+ clearance by a novel mechanism utilizing the insertion of secretory vesicle Na-Ca exchangers into the plasma membrane during exocytosis.
authors.affiliation: Department of Pharmacology and Neuroscience, Albany Medical College, New York 12208, USA.
authors.forename: Y M
authors.initials: YM
authors.lastname: Tang
authors.forename: E R
authors.initials: ER
authors.lastname: Travis
authors.forename: R M
authors.initials: RM
authors.lastname: Wightman
authors.forename: A S
authors.initials: AS
authors.lastname: Schneider
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000378:metabolism / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology*; D018613:Microscopy, Confocal; D015398:Signal Transduction / Q000502:physiology*; D012964:Sodium / Q000172:deficiency / Q000502:physiology; D019831:Sodium-Calcium Exchanger / Q000502:physiology*
chemical_list: D002395:Catecholamines; D019831:Sodium-Calcium Exchanger; D012964:Sodium; D002118:Calcium