The influence of verapamil on the amplitude and frequency of cholinergic-initiated contractions of isolated gastric muscularis muscle of Bufo marinus.

In order to elucidate the role of Ca2+ in the acetylcholine-initiated amplitude and frequency of spontaneous contractions of isolated circular muscle strips from Bufo marinus stomach, we investigated the effects of omission of Ca2+ in the nutrient fluid and also the influence of verapamil, a calcium antagonist, on the amplitude and frequency of the initiated spontaneous contractions. The gastric muscularis muscle strips were prepared and mounted in an organ bath. The control preparation was challenged with a predetermined dose of acetylcholine (1.50 x 10(-5) mol/l) to elicit isometric contractions and there was no decline in the strength of contractions during the experimental period (2 h). Omission of Ca2+ in the nutrient solution prevented acetylcholine-initiated contractions. When the preparation was challenged with the concentration of acetylcholine in the presence of different concentrations of verapamil(10(-10)-10(-3) mol/l), verapamil concentration-dependently suppressed the amplitude of acetylcholine-initiated contractions. When the contractions were seen the frequency was identical. From this investigation, it was concluded that Ca2+ plays a significant part in acetylcholine-initiated spontaneous contractions of circular gastric muscularis muscle of B. marinus.