Differential antagonism by glibenclamide of the relaxant effects of cromakalim, pinacidil and nicorandil on canine large coronary arteries.

The relaxant mechanisms of action of cromakalim, pinacidil and nicorandil, potassium channel openers, on large epicardial coronary arteries were investigated in isolated canine left circumflex arteries contracted by 10(-7) mol/l U46619, a thromboxane A2 analogue, or addition of 25 mmol/l KCl in comparison with nitroglycerin. Cromakalim (3 x 10(-8)-3 x 10(-5) mol/l), pinacidil (10(-6)-10(-4) mol/l), nicorandil (3 x 10(-6)-10(-3) mol/l) and nitroglycerin (3 x 10(-8)-10(-5) mol/l) all produced a concentration-dependent relaxation in both U46619- or KCl-contracted arteries. At their maximum effects pinacidil, nicorandil and nitroglycerin produced full relaxation in arteries contracted by either means. In contrast, cromakalim produced about a 73% relaxation in KCl-contracted arteries, although it caused full relaxation in U46619-contracted ones. In the presence of glibenclamide the concentration-relaxation curves for cromakalim in U46619- or KCl-contracted arteries underwent rightward parallel shifts. Schild regression had a slope of 1.00 and yielded a pA2 of 7.47 for glibenclamide in U46619-contracted arteries, and corresponding values obtained in KCl-contracted arteries were 0.86 (not significantly different from unity) and 7.28. The concentration-relaxation curves for pinacidil in U46619-contracted arteries also underwent rightward parallel shifts in the presence of glibenclamide, however, Schild regression had a slope of 0.60. The concentration-relaxation curves for pinacidil in KCl-contracted arteries underwent rightward parallel shifts only to a limited extent in the presence of glibenclamide. The concentration-relaxation curves for nicorandil and nitroglycerin in U46619- or KCl-contracted arteries were not affected by glibenclamide in concentrations which antagonized cromakalim.(ABSTRACT TRUNCATED AT 250 WORDS)