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.

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 KCl-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 KCl-contracture in a Na+-free sucrose solution may be less energy-dependent as compared with that in a Na+-free Tris medium.(ABSTRACT TRUNCATED AT 250 WORDS)