MECHANISMS OF ECHINOCYTOSIS INDUCED BY CROTALUS-ATROX VENOM

Transient echinocytosis has been reported in association with snake en venomation in humans and dogs. An in vitro model of echinocytosis indu ced by venom of Crotalus aa ox (western diamondback rattlesnake) was e stablished to characterize erythrocyte morphologic changes and to inve stigate potential mechanisms of echinocytic transformation. Erythrocyt e morphologic changes produced after the addition of venom to canine, feline, equine, and human blood were characterized by dose-dependent e chinocytosis. Type III echinocytosis was consistently induced in vitro at a dose comparable to in vivo envenomation; higher venom doses prod uced spheroechinocytic and spherocytic transformations. These changes could not be induced in vitro in the presence of ethylenediaminetetraa cetic acid but were observed in heparinized and citrated blood samples , suggesting the participation of calcium or a metalloprotein in echin ocytic change. These findings suggest that phospholipase A2 (PLA2), a calcium-dependent enzyme in snake venom, may be responsible for echino cytic transformation via the production of lysolecithin, a known echin ocytic agent. Purified PLA2 from C. atrox venom induced dose-dependent echinocytic change in vitro in canine brood. Other potential mechanis ms of echinocytic change evaluated in canine blood included erythrocyt e cation loss and erythrocyte ATP depletion. In canine blood mixed wit h venom, erythrocyte sodium and potassium concentrations were consiste ntly less than those of controls, likely as a result of membrane alter ations produced by the actions of PLA2. There was no difference in blo od ATP concentrations from dogs with snakebite when compared with norm al controls; however, the power of this comparison was low. Echinocyto sis induced by rattlesnake venom is related to the degree of venom exp osure and may correlate clinically with the amount of venom absorbed. Echinocytic transformation in vitro is induced by PLA2 present in veno m.