Effects of calcium on acid secretion from the rat isolated gastric mucosa during stimulation with histamine, pentagastrin, methacholine and dibutyryl cyclic adenosine-3',5'-monophosphate.

1. An isolated gastric mucosal preparation from immature rats is described. The mucosal surface was superfused and acid secretion was recorded continuously by monitoring H+ -ion concentration. 2. Repeated stimulation with submaximal concentrations of histamine or dibutyryl cyclic adenosine 3',5'-monophosphate (db cyclic AMP) produced consistent responses. Secretion induced by pentagastrin and methacholine demonstrated varying degrees of tachyphylaxis. All responses were readily reversed on washing out the secretagogue. 3. Reduction of Ca2+ from 3.6 mM increased responses to histamine, pentagastrin and methacholine while increase of Ca2+ to 7.2 mM decreased responses. Db cyclic AMP-induced secretion was not influenced by external Ca2+. 4. When Mg2+ was raised from 1.2 mM responses to histamine and pentagastrin increased. Replacement of Ca2+ with Mg2+ produced a transient increase followed by a decrease in responses. 5. The similarity of the effects of Ca2+ on pentagastrin, methacholine and histamine indicates that neither pentagastrin nor methacholine act via Ca2+ -dependent histamine release.