Effects of Sucrose- or Tris-Substitution for Na+ on Responses to D 600, Papaverine and KCN in the K+-Depolarized Taenia Coli of Guinea Pigs

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Effects of D 600, papaverine and KCN on sustained contracture induced by 20 mM KCl in a Na+-free sucrose- or Tris-substituted solution were investigated in the taenia coli of guinea pigs. D 600 (10−5 M) and papaverine (10−4 M), added after 40 min incubation in the 20 mM KCl 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 KCl Tris solution. The cellular Na+ content of the taenia coli 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 coli 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.