Ryanodine inhibits caffeine-evoked Ca2+ mobilization and catecholamine secretion from cultured bovine adrenal chromaffin cells.
The effects of ryanodine, a selective inhibitor of the Ca(2+)-induced Ca2+ release mechanism, on caffeine-evoked changes in cytosolic Ca2+ concentration ([Ca2+]i) and catecholamine secretion were investigated using cultured bovine adrenal chromaffin cells. Caffeine (5-40 mM) caused a concentration-dependent transient rise in [Ca2+]i and catecholamine secretion in Ca2+/Mg(2+)-free medium containing 0.2 mM EGTA. Ryanodine (5 x 10(-5) M) alone had no effect on either [Ca2+]i or catecholamine secretion. Although the application of ryanodine plus caffeine caused the same increase in both [Ca2+]i and catecholamine secretion as those induced by caffeine alone, ryanodine (4 x 10(-7) - 5 x 10(-5) M) irreversibly prevented the increase in both [Ca2+]i and catecholamine secretion resulting from subsequent caffeine application over a range of concentrations. The secretory response to caffeine was markedly enhanced by replacement of Na+ with sucrose in Ca2+/Mg(2+)-free medium, and this enhanced response was also blocked by ryanodine. Caffeine was found to decrease the susceptibility of the secretory apparatus to Ca2+ in digitonin-permeabilized cells. These results indicate that caffeine mobilizes Ca2+ from intracellular stores, the function of which is irreversibly blocked by ryanodine, resulting in the increase in catecholamine secretion in the bovine adrenal chromaffin cell.
Department of Pharmacology, Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
H
H
Teraoka
Y
Y
Nakazato
A
A
Ohga
D000311:Adrenal Glands / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002463:Cell Membrane Permeability / Q000187:drug effects; D002838:Chromaffin System / Q000166:cytology / Q000378:metabolism*; D004072:Digitonin / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology*; D012964:Sodium / Q000494:pharmacology
D002395:Catecholamines; D012433:Ryanodine; D002110:Caffeine; D012964:Sodium; D004072:Digitonin; D002118:Calcium