Inhibition by Ro 31-8220 of acid secretory activity induced by carbachol indicates a stimulatory role for protein kinase C in the action of muscarinic agonists on isolated rat parietal cells

Abstract

The bisindolylmaleimide Ro 31-8220 is a selective inhibitor of protein kinase C. This compound was used to investigate the involvement of protein kinase C in the stimulation of gastric acid secretion by the muscarinic cholinergic receptor on rat isolated parietal cells. The accumulation of the weak base aminopyrine by both crude and enriched preparations of parietal cells was used as an index of secretory activity. Ro 31-8220 antagonized (IC50, 1.0 microM) the effect of the activator of protein kinase C,12-O-tetradecanoylphorbol 13-acetate (TPA), on histamine-stimulated aminopyrine accumulation. Ro 31-8220 (0.1-2.14 microM) inhibited the aminopyrine response to 0.1 mM carbachol (IC50, 0.78 microM; 49% inhibition at 2.14 microM Ro 31-8220) and shifted the dose-response curve for the effect of carbachol concentration of aminopyrine accumulation downwards and to the right. No inhibition of aminopyrine accumulation induced by histamine was found with Ro 31-8220 (0.1-2.14 microM). In a preparation containing > 80% parietal cells incubated with 0.1 mM carbachol, 2.14 microM Ro 31-8220 inhibited aminopyrine accumulation by 43%, but had no effect on the increase in intracellular Ca2+ which was measured by using the fluorescent probe FURA-2. In conclusion, Ro 31-8220 (0.1-2.14 microM) produced a selective reduction in secretory activity in parietal cells by inhibition of protein kinase C. The predominant role of protein kinase C in parietal cells activated with carbachol is not to cause feedback inhibition of the response but to facilitate stimulation of secretory activity.