The mode of contractile action of palytoxin in isolated vascular smooth muscle of guinea-pig aorta

Abstract

The mode of action of palytoxin (Palythoa tuberculosa) on the contractile responses and ion movements in guinea-pig aorta was investigate^. Experiments were conducted in the presence of phentolamine (10 M). PTX (10 M) induced a contraction with a latency period of about 1 min, and it reached maximum after about 20 min. The contraction induced by PTX was rapidly abloished by a removal nf external Ca. Readdition of Ca restored the contraction. Verapamil, which markedly antagonized the contraction induced by high-K depolarization, decreased the rate of rise of the PTX-induced contraction, but did not inhibit the sustained tension level. Removal of external Na markedly inhibited the contraction induced by PTX, while it had no effect on the contrction induced by histamine. PTX rapidly decreased tissue K content with a similar time course as that for the increase in tension. Ouabain (10-4 M) also decreased tissue K content in the muscle, but the rate of these changes was much solwer than the PTX-induced ones. PTX increased cellular Ca content (measured by a modified ‘La method’) in normal solution but not in Na deficient solution. These results suggest that the PTX-induced contraction in guinea-pig aorta is due to an increase in membrane Na permeability.