Cardiotoxins from Cobra Venoms: Possible Mechanisms of Action

Abstract

AbstractIn addition to the postjunctional neurotoxins that bind to acetylcholine receptors, cobra venoms contain large quantities of similar polypeptides that act directly on cell membranes. These toxins (“cardiotoxins”, “cytotoxins”, “direct lytic factors”, “membrane toxins”) act in vivo to stop the heart in systole. They also cause depolarization and contracture of smooth and skeletal muscles, and depolarization of nerve cells. In higher concentrations, cardiotoxins lyse erythrocytes, an effect which is very pronounced in the presence of small amounts of phospholipase A2.There is no clear understanding of the mechanism of action of cardiotoxins. The nature of their binding site has not been elucidated, but high concentrations of Ca2+ prevent their binding to membranes. This, together with the basic nature of the toxins, implicates a negatively-charged membrane component. Despite the attractions of negatively-charged phospholipids found in studies with artificial membranes, such lipids are probably not i...