Abstract
Effects of D 600, papaverine and KCN on sustained contracture induced by 20 mM KCI in a Na+-free sucrose- or Tris-substituted solution were investigated in the taenia coil of guinea pigs. D 600 (10-5 M) and papaverine (10-4 M), added after 40 min incubation in the 20 mM KCI sucrose solution, relaxed the muscle by 88.2±8.0% (mean±S.E., n=4) and 78.8±6.3% (n=4), respectively. In contrast to this, KCN (10-3 M) relaxed the muscle by 11.0±4.7% (n=4) after a 20 min incubation in the sucrose solution. The concentration-relaxation curves for these relaxants were slightly shifted to the right in the Na+-free 20 mM KCI Tris solution. The cellular Na+ content of the taenia coil was greatly reduced by exposure to the sucrose or Tris solution, while the Ca2+ contents in both solutions were gradually increased with the exposure time. When a glucose-free solution was applied 60 min after the KCI-induced sustained contracture, gradual relaxation in the normal solution was observed. This relaxation was completely inhibited in the Na+-free sucrose solution. These results suggest that the relaxing activities of the different inhibitors are changed to different degrees by the replacement of Na+ with sucrose in the guinea-pig taenia coil and that sustained KCI-contracture in a Na+-free sucrose solution may be less energy-dependent as compared with that in a Na+-free Tris medium. These results also indicate the inability to directly correlate the changes in the Ca2+ and Na+ contents with the greatly reduced activities of the relaxants in a Na+-free sucrose solution.
