[Ba-induced contraction of the guinea pig ileal longitudinal muscle and its inhibition by D-600, benactyzine, and papaverine].

In the guinea-pig ileal longitudinal smooth muscle, Ba caused an initial phasic contraction, followed by a gradual decrease of the contraction (tonic contraction). In the Ca-free and the Ca-free, K-rich physiological solution, Ba could also contract the longitudinal muscle, but 30 min- and 60 min-immersion of the tissue in the Ca-free solution decreased lower than 20% of control of the Ba contraction. Although the K-induced depolarization intensified the Ba contraction after the 30 min-immersion, within 10 min after the immersion in the two solutions there is no difference in the height of Ba contractions. In the normal physiological solution, Ba seems to serve the contractile protein with free Ca ions rather than itself for the Ba contraction. D-600 induced an equal inhibition on the Ba contractions in the normal physiological solution and in the Ca-free solution, and it inhibited the tonic contraction more than the phasic one. The phasic component may be due to the cellular Ca mobilized by Ba which passes through D-600-sensitive pathway, and at least part of the tonic component may utilize the extracellular Ca. Benactyzine perferentially inhibited the Ba contraction in the Ca-free solution, and it depressed the phasic component more than the tonic one. Treatment with papaverine induced an equal inhibition on the phasic and tonic components of Ba contractions and the Ba contraction in the Ca-free solution. Benactyzine may exert the main influence on the mobilization of the cellular Ca through the competition with Ca. Papaverine seems to inhibit the Ba contractions by diverse actions.