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

Abstract

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. Repeated stimulation with submaximal concentrations of histamine or dibutyryl cyclic adenosine 3′,5′‐monophosphate (db cyclic AMP) produced consistent responses. Secretion induced by pentagas‐trin and methacholine demonstrated varying degrees of tachyphylaxis. All responses were readily reversed on washing out the secretagogue. Reduction of Ca 2+ from 3.6 m m increased responses to histamine, pentagastrin and methacholine while increase of Ca 2+ to 7.2 m m decreased responses. Db cyclic AMP‐induced secretion was not influenced by external Ca 2+ . When Mg 2+ was raised from 1.2 m m responses to histamine and pentagastrin increased. Replacement of Ca 2+ with Mg 2+ produced a transient increase followed by a decrease in responses. The similarity of the effects of Ca 2+ on pentagastrin, methacholine and histamine indicates that neither pentagastrin nor methacholine act via Ca 2+ ‐dependent histamine release.