Interaction of signal transduction pathways in mediating acid secretion by rat parietal cells

To examine the role of protein kinase C (PKC) on the acid secretory activity of isolated rat parietal cells, histamine-and dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP)-stimulated [14C]aminopyrine accumulation was determined in the presence of agents that redistribute PKC activity to plasma membranes. Phorbol 12-myristate 13-acetate (PMA), 1-oleoyl-2-acetylglycerol (OAG), and phospholipase C inhibited, in a dose-dependent fashion, histamine- and DBcAMP-stimulated [14C]aminopyrine accumulation. Because PKC inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7) reversed the effect, the results suggest that inhibition of histamine- or DBcAMP-stimulated [14C]aminopyrine accumulation induced by PMA, OAG, or phospholipase C was caused by increased activity of PKC in plasma membrane. To determine where in the cascade of events PKC inhibits acid secretion, histamine-, cholera toxin-, and forskolin-stimulated [14C]aminopyrine accumulation was measured with or without PMA. Because the percent of inhibition by PMA of [14C]aminopyrine accumulation was similar with the three secretagogues, the results suggest that PKC inhibits acid secretion at a point beyond adenosine 3',5'-cyclic monophosphate (cAMP) production. This was supported by the fact that PMA had no effect on histamine-stimulated production of cAMP and by the finding that activation of PKC had the same effect on histamine- or DBcAMP-stimulated [14C]aminopyrine accumulation. Histamine and DBcAMP inhibited PKC activity, suggesting a reciprocal interaction between PKC and histamine-triggered signal transduction pathway.