Effect of palytoxin on endothelium-dependent and -independent relaxation in rat aortic rings

Endothelium inhibits the palytoxin-induced depolarization and Ca2+ mobilization in porcine coronary artery through endothelium-derived hyperpolarizing factor and nitric oxide released by palytoxin

Palytoxin induced increases in cytosolic Ca2+ and tension, which were dependent on external Ca2+, and depolarized the membrane in endothelium-denuded porcine coronary arteries. When the endothelium was present, however, these effects were greatly inhibited, suggesting that some factors from endothelium inhibited the palytoxin-actions. Pretreatment with 100 microM N omega-nitro-L-arginine partially reversed the inhibitory effect of endothelium on the Ca2+ movement and the contraction but not that on the depolarization. Pretreatment with 10 microM indomethacin did not affect the inhibition. These results suggest that palytoxin released both nitric oxide and endothelium-derived hyperpolarizing factor (EDHF) from the endothelium, both of which counteracted the actions of palytoxin on smooth muscle cells. It is thought that the palytoxin-induced depolarization was attenuated by hyperpolarization due to EDHF.