Stimulation of gastric acid and bicarbonate secretions by calcium in guinea pig stomach and amphibian isolated mucosa.

Administration of Ca++ (1.5 mg/kg i.v.) increased the output of both H+ and HCO-3 from the stomach of the anesthetized guinea pig as determined by measurement of gastric intraluminal pH and pCO2. The rise in HC-3 secretion was slightly greater than that in H+, resulting in a decrease in net acidity. Fundic mucosa isolated from frogs was used to study the mechanisms of the stimulatory actions. An increase in Ca++ concentration in the nutrient (serosal) bathing solution from 1.8 to 7.2 mM stimulated H+ transport in this preparation. The effect of raising Ca++ concentration was inhibited by the histamine H2 receptor antagonist Metiamide and by increasing nutrient Mg++. Stimulation of H+ transport, sensitive to Metiamide, was also observed with the calcium ionophore A23187 (4 micrograms/ml, nutrient side). The results indicate that at the mucosal level, Ca++ stimulates H+ transport by release of histamine from mucosal stores with properties similar to those of mast cells. Transport of HCO-3 in isolated mucosae was studied after inhibition of H+ transport my metiamide. An increase in nutrient Ca++ concentration stimulated the HCO-3 transport but the calcium ionophore had no effect. This action of Ca++ was abolished by atropine (10(-6) M) and by raising nutrient Mg++, suggesting that it reflects release of acetylcholine from intramucosal nervous tissue. Thus Ca++ stimulated gastric transport of both H+ and HCO-3 in vivo and in vitro but evidence for a direct action on the transporting (parietal and epithelial) cells was not obtained.