DIFFERENTIAL VASORELAXANT EFFECTS OF LEVCROMAKALIM AND P1060 IN THE ISOLATED KCL-PRECONTRACTED AND RBCL-PRECONTRACTED HUMAN SAPHENOUS-VEIN - POSSIBLE INVOLVEMENT OF INTRACELLULAR CA2+ STORES

The influence of rubidium-substituted physiological salt solution (Rb- PSS) on the relaxant effects of K+ channel openers was investigated in the human saphenous vein. In tissues precontracted with 20 mM KCl (in K-PSS) levcromakalim and P1060 produced complete, sustained relaxatio ns. However, in Rb-PSS (containing 20 mM RbCl) these effects were inhi bited and, although complete relaxations still occurred, were transien t. When caffeine was applied at the beginning of this fade of levcroma kalim-induced relaxation in Rb-PSS its contractile effect was potentia ted. Similarly, the contraction to noradrenaline was potentiated when applied at the beginning of this fade of levcromakalim-induced relaxat ion, whereas this response was attenuated in control tissues bathed in 20 mM KCl (in K-PSS). Our results show that the relaxant effects of K + channel openers in human saphenous vein are inhibited in Rb-PSS, in agreement with previous studies in animal tissue, and suggest that an increased Ca2+ uptake into intracellular stores may be contributory to vasorelaxation.