Different actions of protein kinase C isoforms α and ε on gastric acid secretion

The phorbol ester TPA, an activator of protein kinase C (PKC), inhibits cholinergic stimulation of gastric acid secretion but increases basal H + secretion. Since these contradictory findings suggest the action of different PKC isozymes we analysed the role of calcium‐dependent PKC‐α, and calcium‐independent PKC‐ε in gastric acid secretion. Inhibition of PKC‐α by the indolocarbazole Gö 6976 revealed that about 28% of carbachol‐induced acid secretion was inhibited by PKC‐α. In the presence of Gö 6976 approximately 64% of the carbachol‐induced signal transduction is mediated by Ca 2+ /calmodulin‐dependent protein kinase II (CaMKII), and 14% is conveyed by PKC‐ε as deduced from the inhibition with the bisindolylmaleimide Ro 31‐8220. Inhibition of carbachol‐induced acid secretion by TPA was accompanied by a decrease in CaMKII activity. The stimulation of basal acid secretion by TPA was biphasic with a peak at a very low concentration (10 p M ), resulting in an activation of the calcium‐sensor CaMKII. The activation was determined with a phosphospecific polyclonal antibody against active CaMKII. The TPA‐induced increase of H + secretion was sensitive to the cell‐permeable Ca 2+ ‐chelator BAPTA/AM, Ro 31‐8220, and the CaMKII‐inhibitor KN‐62, but not to Gö 6976. Since TPA induced the translocation of PKC‐ε but not of PKC‐α in resting parietal cells, PKC‐ε seems to be at least responsible for an initial elevation of free intracellular calcium to initiate TPA‐induced acid secretion. Our data indicate the different roles of two PKC isoforms: PKC‐ε activation appears to facilitate cholinergic stimulation of H + ‐secretion likely by increasing intracellular calcium. In contrast, PKC‐α activation attenuates acid secretion accompanied by a down‐regulation of CaMKII activity.British Journal of Pharmacology (2002) 136 , 938–946. doi: 10.1038/sj.bjp.0704790