PKC theta activity maintains normal quantal size in chromaffin cells.

Protein kinase C (PKC) activity mediates multiple neurosecretory processes, but these are poorly understood due in part to the existence of at least 12 PKC isoforms. Using amperometry to record quantal catecholamine release from chromaffin cells, we found that both broad spectrum PKC antagonists and rottlerin, a selective inhibitor of the novel isoforms PKC theta and PKC delta, decreased quantal size and the number of secretory events recorded per stimulus. In contrast, drugs that selectively inhibit the atypical and conventional PKC isoforms had no effect on these parameters. While both PKC theta and delta were expressed in chromaffin cells, mice deficient for PKC theta, but not for PKC delta, exhibited lower quantal size than wild-type and were insensitive to rottlerin. Finally, an inhibitory PKC theta pseudosubstrate produced rottlerin-like responses in wild-type mice, indicating that the lack of rottlerin response in the PKC theta mutants was not the result of a form of compensation. These findings demonstrate neurosecretory regulation by a novel PKC isoform, PKC theta, and should contribute to defining mechanisms of activity-dependent regulation of neurosecretion.