The contractile action of palytoxin in the isolated rabbit urinary bladder

Palytoxin at 10(-10)-10(-7) M caused contractions of the detrusor muscle from rabbit urinary bladder in a concentration-dependent manner. The response to palytoxin was markedly inhibited by indomethacin (a cyclooxygenase inhibitor) or nordihydroguaiaretic acid (a lipoxygenase inhibitor) at 10(-5) M. Indomethacin and nordihydroguaiaretic acid also inhibited the response to arachidonic acid at 10(-3) M. A Ca2+-free medium with EGTA or nifedipine at 10(-5) M, nearly abolished the responses to palytoxin and arachidonic acid. Tetrodotoxin, phentolamine, atropine and chlorpheniramine (all at 10(-5) M) had a slight or no inhibitory effect on the response to palytoxin. These results suggested that in the rabbit bladder, the contractile effect of palytoxin is mainly dependent on an increase in metabolites of arachidonic acid.