Abstract
We have used membrane capacitance measurements to assay Ca 2+-triggered exocytosis in single bovine adrenal chromaffin cells. Brief application of phorbol ester (PMA) enhances depolarization-evoked exocytosis severalfold while actually decreasing the Ca 2+ current. Ca 2+ metabolism is unchanged. Three different protocols were used to show that PMA increases the size of the readily releasable pool of secretory granules. PMA treatment leads to a large increase in amplitude, but little change in the time course of the exocytic burst that results from rapid elevation of [Ca 2+] i upon photolysis of DM-Nitrophen. Thus, PKC appears to affect a late step in secretion but not the Ca 2+ sensitivity of the final step.
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