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The mechanism of action of maitotoxin in relation to Ca 2+ movements in guinea‐pig and rat cardiac muscles
Author(s) -
Kobayashi Masaki,
Ohizumi Yasushi,
Yasumoto Takeshi
Publication year - 1985
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1985.tb08907.x
Subject(s) - verapamil , tetrodotoxin , guinea pig , chronotropic , propranolol , reserpine , medicine , inotrope , endocrinology , ventricle , cardiac muscle , chemistry , guanethidine , pharmacology , biology , calcium , heart rate , stimulation , blood pressure
1 Maitotoxin (MTX), the most potent marine toxin known, produced a dose‐dependent positive inotropic effect on guinea‐pig isolated left atria and rat ventricle strips at concentrations of 0.1 ng to 4 ng ml −1 . MTX (4 ng ml −1 ) also exhibited a positive chronotropic effect on guinea‐pig right atria. 2 The MTX‐induced inotropic effect was almost abolished by Co 2+ or verapamil, but was little affected by propranolol, reserpine or tetrodotoxin. 3 The tissue Ca content of guinea‐pig left atria was increased by MTX (2–30 ng ml −1 ) in a dose‐dependent manner, and this increase was markedly inhibited by Co 2+ or verapamil. 4 Furthermore, on the rat isolated cardiac myocytes MTX (0.01–10 ng ml −1 ) caused an arrhythmogenic effect which was followed by their transformation into irreversibly rounded cells. The effects of MTX on the isolated cells were inhibited by verapamil or Ca 2+ ‐free solution. 5 These results suggest that the excitatory effects of MTX on heart muscle are caused by a direct action on the cardiac muscle membrane mainly due to an increase in Ca 2+ permeability.