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Contractile response of the rabbit aorta to maitotoxin, the most potent marine toxin.
Author(s) -
Ohizumi Y,
Yasumoto T
Publication year - 1983
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1983.sp014650
Subject(s) - verapamil , methysergide , contraction (grammar) , chemistry , phentolamine , antagonism , aorta , tetrodotoxin , toxin , marine toxin , medicine , endocrinology , propranolol , calcium , pharmacology , biochemistry , receptor , biology , antagonist , organic chemistry
Maitotoxin (MTX), the most potent marine toxin, caused a dose‐dependent contraction of the rabbit isolated aorta at concentrations of 10(‐10)‐3 X 10(‐8) g/ml. The dose‐contractile response curve for MTX was shifted to the right in a parallel manner by verapamil (10(‐6) M), was slightly shifted to the right by phentolamine (10(‐6) M) and was not or little affected by tetrodotoxin, methysergide, chlorpheniramine or indomethacin. The MTX‐induced contraction was abolished by incubation in Ca2+‐free medium and was increased in a linear fashion with Ca2+ concentrations between 0.03 and 1.2 mM. In Ca2+‐free solution, the contractile responses produced by re‐introduction of Ca2+, Sr2+ or Ba2+ were potentiated after treatment with MTX (10(‐8) g/ml.) and a high concentration of KCl (4 X 10(‐2) M). After treatment with verapamil (10(‐7)‐10(‐6) M), the dose‐contractile response curve for Ca2+, Sr2+ or Ba2+ in the presence of MTX or KCl was shifted to the right in a parallel manner, indicating competitive antagonism. But the dose‐response curve for Ca2+ in the presence of A23187 (3 X 10(‐5) M), a Ca ionophore, was not affected at all by verapamil (10(‐6) M). The tissue Ca content of the aorta was increased 31% by treatment with MTX (10(‐8) g/ml.). This effect of MTX was markedly inhibited in the presence of verapamil. On the basis of these results, it is suggested that the MTX‐induced contraction of the aorta is caused mainly by a direct action on smooth muscle, possibly due to an increase in Ca2+ permeability which occurred through voltage‐sensitive Ca2+ channels in the smooth muscle cell membrane.