title: The mechanism of action of maitotoxin in relation to Ca2+ movements in guinea-pig and rat cardiac muscles.
abstract: 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. The MTX-induced inotropic effect was almost abolished by Co2+ or verapamil, but was little affected by propranolol, reserpine or tetrodotoxin. 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 Co2+ or verapamil. 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 Ca2+-free solution. 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 Ca2+ permeability.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008387:Marine Toxins / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism*; D035964:Oxocins; D051381:Rats; D011919:Rats, Inbred Strains; D012110:Reserpine / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013045:Species Specificity; D014700:Verapamil / Q000494:pharmacology; D000095702:Polyether Toxins
chemical_list: D002118:Calcium; D008387:Marine Toxins; D035964:Oxocins; D012110:Reserpine; D000254:Sodium-Potassium-Exchanging ATPase; D014700:Verapamil; C020394:maitotoxin; D000095702:Polyether Toxins