Relaxing action of okadaic acid, a black sponge toxin on the arterial smooth muscle

Vasodilator responses induced by okadaic acid were investigated in isolated pig coronary artery and dog basilar artery precontracted with high K. Okadaic acid showed the relaxing effect at the concentrations above 3 x 10(-7)M. The relaxation was not inhibited by the treatment with various receptor antagonists, indomethacin, ouabain and high concentration of Ca2+ (7.5mM) and by the removal of endothelium. The intracellular Ca2+ level measured with fura 2 was not changed apparently in spite of the relaxation by okadaic acid. The maximum rate of relaxation was slowed under the conditions of low temperature (30 degrees C), anoxia and by the addition of 2-deoxy-D-glucose instead of glucose. These results suggest that okadaic acid causes vasodilation probably by its intracellular effect on Ca2+ sensitivity of contractile elements, and the ATP-producing system may be involved in this relaxation.