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

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Abstract
Administration of Ca++ (1.5 mg/kg i.v.) increased the output of both H+ and HCO3‐ from the stomach of the anesthetized guinea pig as determined by measurement of gastric intraluminal pH and pCO2. The rise in HCO3‐ 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 μg/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.