Electro-mechanical coupling in the complex stomach smooth muscles.

In the majority of experiments the ruminal preparations did not exhibit spontaneous electrical and contractile activity but showed a Ca-dependent spike-free myogenic tone. Ba2+ or Sr2+ evoked spike activity and phasic contractions and increased the muscle tonic tension. Tetraethylammonium (TEA) exerted no effect on the ruminal preparations but potentiated the effect of Ba2+. Acetylcholine (ACh) induced dose-dependent spike-free tonic contractions which were verapamil resistant and were suppressed by sodium nitroprusside. When applied to BaCl2- or TEA-pretreated preparations ACh caused spike activity and phasic contractions. The antral abomasum exhibited a spontaneous electrical activity--slow waves on which spike potentials were superimposed. ACh and TEA induced membrane depolarization and increased the spike activity and the phasic contraction amplitude.