Investigation of the role of extracellular calcium in the control of acid secretion in the isolated whole stomach of the rat.

1 An isolated stomach preparation from immature rats has been used to study the role of extracellular calcium in the control of gastric acid secretion. Calcium was removed from both the serosal and mucosal solutions either in the absence of a chelating agent or in the presence of EGTA.2 Removal of calcium in the absence of EGTA had no significant effect on basal acid secretion or the acid responses to gastrin and dibutyryl cyclic adenosine 3',5'-monophosphate (db cyclic AMP). Under the same conditions there was a marked potentiation of the acid response to histamine, and a reduction of the acid response to acetylcholine which was readily reversed on restoring calcium to the bathing solutions.3 Removal of calcium in the presence of EGTA caused an inhibition of basal acid secretion and of the acid responses to histamine and db cyclic AMP. In each case this reduction in acid output was readily reversed on bathing the stomachs in normal calcium-containing (2.5 mM Ca(2+)) EGTA-free solutions.4 The inhibition of the acid response to histamine produced by Ca(2+)-free solutions which contained EGTA was not reversed on bathing the stomachs in solutions that contained both EGTA (0.1 mM) and an excess of calcium (2.5 mM).5 The removal of extracellular calcium in the absence of EGTA provided evidence that the secretion of H(+) ions is dependent under some conditions on calcium ions. The possibility cannot be excluded that EGTA itself exerts an inhibitory influence on the process of acid secretion.