Some degree of overlap exists between the K(+)-channels opened by cromakalim and those opened by minoxidil sulphate in rat isolated aorta

Abstract

The effects of the K+ channel opening drugs minoxidil sulphate and cromakalim, on 42K+ and 86Rb+ efflux and on vasorelaxation in rat isolated aorta, were compared. In rat aortic rings precontracted with noradrenaline (100 nmol/l), minoxidil sulphate and cromakalim concentration-dependently inhibited induced tension by up to 90%, with pD2 values of 7.35 +/- 0.1 and 7.17 +/- 0.1, respectively. Glibenclamide (300 nmol/l), produced 2200- and 19-fold rightward shifts in the concentration-relaxation curves to minoxidil sulphate and cromakalim, respectively, without an effect on the maximum relaxation. Both minoxidil sulphate and cromakalim increased the efflux of 42K+ and 86Rb+ from aorta in a concentration-dependent manner, with midpoints in the mumol/l range; the maximum efflux induced by minoxidil sulphate being approximately one tenth of that induced by cromakalim. The ratio of stimulated 86Rb+/42K+ efflux increased from 0.22 to 0.48 with increasing cromakalim concentrations, but was approximately constant (approximately 0.39) when the minoxidil sulphate concentration was varied. In the presence of minoxidil sulphate, the effects of cromakalim on 42K+ and 86Rb+ efflux were inhibited in a concentration-dependent manner, by up to 60%. In the continuing presence of cromakalim (300 nmol/l), minoxidil sulphate (10 mumol/l)-induced increases in 42K+ and 86Rb+ efflux were inhibited by 45%, whereas conditioning with cromakalim (1 mumol/l) inhibited the 86Rb+ efflux stimulated by additional superfusion of cromakalim (1 mumol/l) by 85%. Glibenclamide inhibited minoxidil sulphate (10 mumol/l)- and cromakalim (1 mumol/l)-induced increases in 42K+ and 86Rb+ efflux in a concentration-dependent manner with IC50 values of approximately 80 nmol/l.(ABSTRACT TRUNCATED AT 250 WORDS)