THE CAFFEINE-SENSITIVE CA-2+ STORE IN BOVINE ADRENAL CHROMAFFIN CELLS - AN EXAMINATION OF ITS ROLE IN TRIGGERING SECRETION AND CA-2+ HOMEOSTASIS

The effect of caffeine on catecholamine secretion and intracellular free Ca2+ concentration ([Ca2+]i) in bovine adrenal chromaffin cells was examined using single fura-2-loaded cells and cell populations. In cell populations caffeine elicited a large (∼200 nM) transient rise in [Ca2+]i that was independent of external Ca2+. This rise in [Ca2+]i triggered little secretion. Single cell measurements of [Ca2+]i showed that most cells responded with a large (> 200 nM) rise in [Ca2+]i, whereas a minority failed to respond. The latter, whose caffeine-sensitive store was empty, buffered a Ca2+ load induced by a depolarizing stimulus more effectively than those whose store was full. The caffeine-sensitive store in bovine chromaffin cells may be involved in Ca2+ homeostasis rather than in triggering exocytosis. © 1990.