Sites of action of protein kinase C on secretory activity in rat parietal cells

Sites at which the calcium-sensitive phospholipid-dependent protein kinase, protein kinase C, may influence acid secretion have been investigated in rat isolated parietal cells. In both crude and enriched preparations of parietal cells incubated in a medium containing 100 mM K+, the activators of protein kinase C, 12-O-tetradecanoylphorbol 13-acetate (TPA) and 1-oleoyl-2-acetyl-glycerol (OAG), produced a dose-dependent stimulation [half-maximally effective concentration (EC50) values of 1 nM and 70 microM, respectively] of aminopyrine accumulation, an index of the sequestration of acid in the cell. In a medium containing 4.5 mM K+, and with no added secretagogues, TPA and OAG did not affect aminopyrine accumulation. Histamine-stimulated aminopyrine accumulation was inhibited by TPA [half-maximally effective inhibitory concentration (IC50) of 2.9 nM]. TPA reduced the histamine-stimulation of the adenosine 3',5'-cyclic monophosphate (cAMP) content of parietal cells (47% inhibition at 100 nM TPA) but also inhibited aminopyrine accumulation at or distal to cAMP-dependent protein kinase. Activators of protein kinase C can produce multiple effects on secretory activity in the rat parietal cell.