Studies on Cardiotoxin and Vasoactive-Substance-Releasing
NATIONAL TAIWAN UNIV TAIPEI PHARMACOLOGICAL INST
Pagination or Media Count:
Lyophilized venom of Naja naja atra was fractionated on column of CM- Sephadex G-50 into 13 fractions by gradient elution with ammonium acetate buffer at pH 5-7. Among them five fractions V-IX were found to be neurotoxic and three X, XII, XIII were cardiotoxic. Intraperitoneal LD50 in mice was 0. 074 micrograms gg for FR. VIII-the major neurotoxic component NT and 1.48 micrograms gg for Fr. XIII-the major cardiotoxic one CT. CT caused contracture, as well as reduction of resting membrane potentials, of the frogs sartorius, chicks biventer cervicis, and rats diaphragm. In the absence of calcium, the contracture was markedly reduced, although the depolarizing effect remained unchanged. Neither contracture nor depolarization was caused by NT. The terminal nerve spikes of the frog sartorius were abolished by CT but unaffected by NT. CT caused systolic arrest of isolated frog hearts and rats atria by reducing the membrane potentials, whereas NT was almost without effect up to . 0001 gml. CT caused a slow contraction of the guinea pig ileum, which was partially antagonized by either atropine or procaine but not by hexamethonium or antihistaminics. The vessels of the rabbit ear were constricted by CT. In cats, CT caused a fall in systolic pressure more than diastolic pressure, accompanied by various ECG changes. Cardiotoxin isolated from cobra venom acts on various excitable cells, predominantly, of not entirely, by reducing the membrane potentials.