The Influence of Verapamil on the Amplitude and Frequency of Cholinergic-Initiated Contractions of Isolated Gastric Muscularis Muscle of Bufo marinus

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Abstract
To elucidate the role of Ca2+ in the acetylcholine-initiated amplitude and frequency of spontaneous contractions of isolated circular muscle strips from B. marinus stomach, the effects of omission of Ca2+ in the nutrient fluid and also the influence of verapamil, a Ca antagonist, on the amplitude and frequency of the initiated spontaneous contractions were investigated. 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 .times. 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 to 10-3 mol/l), verapamil concentration-dependently suppressed the amplitude of acetylcholine-initiated contractions. When the contractions were seen, the frequency was identical. Evidently, Ca2+ plays a significant part in acetylcholine-initiated spontaneous contractions of circular gastric muscularis muscle of B. marinus.

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