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

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.