Effect of viscotoxin on rabbit heart and aorta, and on frog skeletal muscle

Journal/Book: Eur.J.Pharmacol.23,223-231. 1973;

Abstract: The effects of the mistletoe toxins, Viscotoxins Asub 3 and B, onexcitation and contraction processes in isolated preparations ofcardiac, smooth and skeletal muscle were investigated. In lowconcentrations (1-10 mug/ml), Viscotoxin B reduced the isometric twitchand produced contracture and progressive depolarization of rabbitpapillary muscle. These changes were almost completely reversed byincreasing the extracellular calcium concentration from 2.0 to 4.0 mM.In single frog muscle fibres, Viscotoxins Asub 3 and B, 1 mug/ml, causeda progressive depolarization of the cell membrane; associated with thischange, a transient contracture developed. The depolarization could beprevented by an increase in extracellular calcium concentration from 1.8to 12 mM. Rabbit aortic strips were less sensitive to the Viscotoxinsthan heart and skeletal muscle, but in a concentration of 200 mug/ml,Viscotoxin Asub 3 produced a slowly developing contracture that couldnot be reversed by calcium. It is suggested that the Viscotoxins, bybinding to the cell membrane, displace bound calcium from a membranesite.COPYRIGHT BY Elsevier Science BV, Amsterdam, Netherlands END OF DOCUMENT

Keyword(s): viscotoxin

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