EFFECTS OF A PHORBOL ESTER AND ISOQUINOLINE SULFONAMIDES ON RABBIT PARIETAL-CELL FUNCTION

The role of protein kinase C (PKC) on gastric H+ secretion, as measure d by aminopyrine (AP) uptake and other intracellular signal transducti on products, was investigated in isolated rabbit parietal cells using the PKC activator 12-O-tetradecanoyl phorbol 13-acetate (TPA) and seve ral PKC inhibitors, including isoquinoline sulfonamides (H-7, H-8, H-8 9 and HA-1004) and calphostin-C. TPA dose-dependently inhibited histam ine (10(-4) M)- and carbachol (10(-4) M)-stimulated AP uptake without affecting the response to dibutyryl cyclic AMP (10(-3) M). H-7 and cal phostin-C dose-dependently augmented secretagogue-stimulated AP uptake , whereas H-8 and H-89 inhibited the response to secretagogues, and HA -1004 had no effect. H-7 and calphostin-C-induced augmentation of AP u ptake was blocked by a calcium (Ca++) antagonist, lanthanum chloride, which suggests that the enhanced AP response was regulated by extracel lular Ca++. Moreover, H-7 treatment partially reversed the TPA (10(-7) M)-induced inhibition of secretagogue-stimulated AP uptake. TPA reduc ed histamine- and carbachol-stimulated cAMP and inositol 1,4,5-triphos phate production by 50% and 96%, respectively, with a concomitant redu ction of adenylate cyclase and intracellular free Ca++ by 44% and 78%. TPA increased the distribution of membrane-associated PKC by 20% and decreased histamine-stimulated PKA by 30%. In contrast, H-7 inhibited both PKC and protein tyrosine kinase activity in vitro but had no effe ct on these parameters in vivo. The results indicate that TPA-induced inhibition of secretagogue-stimulated AP uptake in PC is presumably me diated by activation of PKC.