Activation of gastro-intestinal smooth muscle induced by the calcium ionophore A23187.

Tension development was recorded in isolated smooth muscle preparations from the guinea-pig, namely circular strips from the fundus and antrum region of the stomach, and taenia coli. The calcium ionophore A23187 (2-10(-6)-2-10(-5) mol/1) induced maximum activity in fundus and taenia coli, and in antrum an activity slightly smaller than that obtained with acetylcholine (ACh) (5-10(-6) mol/1). The ionophore-induced activity could be suppressed by so-called calcium antagonists: D600 (3-10(-6) mol/1) suppressed the ionophore-induced activity of taenia coli completely; phasic and tonic components in the stomach preparations were selectively suppressed by D600 and sodium nitroprusside (10(-6) mol/1), respectively.