The caffeine-sensitive Ca2+ store in bovine adrenal chromaffin cells; an examination of its role in triggering secretion and Ca2+ homeostasis |
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Authors: | T R Cheek A J O'Sullivan R B Moreton M J Berridge R D Burgoyne |
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Institution: | Department of Zoology, University of Cambridge, UK. |
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Abstract: | 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 (approximately 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 (greater than 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. |
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