On the mechanism of stimulation of H+ transport in gastric mucosa by Ca++ ionophore A23187. II. Ca++-cyclic AMP interactions

The possibility of interactions between calcium and cyclic AMP (cAMP) in the mechanism of stimulation of H+ transport by A23187 was studied in the isolated gastric mucosa of the toad Bufo marinus. A23187 stimulated H+ secretion and histamine release. The amount of histamine released by A23187 did not explain the degree of stimulation. Metiamide partially inhibited the response to A23187. Ca++ ionophore produced an overstimulation of secretion after H+ transport had been induced by supramaximal effective concentrations of histamine (10-4 M). In the presence of metiamide, IMX potentiated the response to A23187. Also, in the same condition (metiamide treated) the effects of db-cAMP and A23187 were additive. The results are consistent with an interaction between Ca++ and ionophore-released histamine at the oxyntic cell in the stimulation by A23187. The stimulatory response may be the result of a potentiation between calcium and cAMP at the intracellular level.