Induction of exocytosis in permeabilized pituitary cells by alpha- and beta-type protein kinase C.

Protein kinase C is now recognized to comprise a family of closely related subspecies (PKCs). When cultured rat pituitary cells were permeabilized by digitonin for 5 min in the absence of Ca2+, endogenous PKC activity was decreased by 72%. PKC depletion was also achieved by prior treatment (24 hr) with high concentrations of phorbol 12-myristate 13-acetate (PMA). When purified activated brain PKCs were added for 30 min to PMA-pretreated, digitonin-permeabilized cells, only alpha- and beta- but not gamma-type PKC stimulated luteinizing hormone release. Since PKC was implicated as a mediator of gonadotropin secretion, gonadotropin-releasing hormone might utilize alpha- and beta-type PKCs for stimulation of gonadotropin secretion; alpha- and beta-type PKCs might participate also in other exocytotic responses in diverse biological systems in which PKC was implicated.