Diacylglycerol production, Ca2+ influx, and protein kinase C activation in sustained cellular responses.

I. Introduction THE focus of this review is on the role of protein kinase C (PKC) in the regulation of the secretion of aldosterone from the adrenal glomerulosa cell and of insulin from the β-cell of the Islets of Langerhans. These processes will be considered in the context of a model of how PKC functions as one component of a three-component, Ca2+-influx-diacylglycerol (DAG)-PKC, plasma membrane transducer involved in regulation of the sustained phase of these secretory responses. Within this context, the possible role of this transducer in the phenomenon of time-dependent potentiation (TDP) and time-dependent suppression (TDS) of these responses will also be considered. The initial physiological system in which the activation of PKC was reported to play a signaling role was that of platelet activation. In their initial studies, Takai et al. (1) showed that activation of both the calcium-calmodulin-dependent myosin light chain kinase, and PKC, a phospholipid- and calcium ion-dependent enzyme, were neces...