Inhibitory effect of calmodulin inhibitors on palytoxin-induced K+ release from rabbit erythrocytes

Palytoxin (PTX) caused K+ release from rabbit erythrocytes at a concentration as low as 10(-11) M. The K+ release due to PTX at a concentration below 10(-9) M was dependent on Ca2+ in medium. The effect of Ca2+ was substituted fully by Sr2+ and partially by Ba2+. W-7 (2 X 10(-4) M), a known inhibitor of calmodulin, markedly inhibited the rate of K+ release due to PTX. W-5 (2 X 10(-4) M), an analog of W-7 with lower affinity to calmodulin than W-7, showed weaker inhibition. Other calmodulin antagonists, such as prenylamine, chlorpromazine and compound 48/80, also inhibited the PTX-induced K+ release. These results suggest that the K+ release induced by PTX involves the process(es) mediated by intracellular Ca2+ and calmodulin.