PURIFICATION AND PHYSIOLOGICAL CHARACTERIZATION OF NEUROTOXINS FROM VENOMS OF THE SCORPIONS CENTRUROIDES-SCULPTURATUS AND LEIURUS-QUINQUESTRIATUS

Abstract

Several toxins having specific effects on the kinetics of Na channels were isolated from the venoms of 2 scorpions. A combination of 2 steps of ion-exchange chromatography was used to purify these toxins, whose sizes and purities were assayed by gel filtration, urea/sodium dodecylsulfate/polyacrylamide gel electrophoresis and isoelectric focusing. The actions of the toxins and their relative potencies were determined by studying the modifications they produced in action potential shape, using the sucrose-gap method, and in ionic current kinetics, measured under voltage-clamp, both assays performed on myelinated axons of frogs and toads. The venom of L. quinquestriatus scorpions yielded 2 active neurotoxins; the major neurotoxin had a mass of .apprx. 7000 daltons. This major toxin affected the Na channel inactivation process exclusively, slowing the rates of inactivation and preventing complete inactivation from occurring in some channels. Such slowed and incomplete Na inactivation resulted in action potentials that were prolonged, from their usual duration of 5-8 ms to hundreds of ms or even s. Five toxins were isolated from the venom of C. sculpturatus scorpions, all of which also had masses of .apprx. 7000-7500 daltons. Four toxins acted primarily on the activation process of Na channels, producing a novel increase in Na permeability upon repolarization of the nerve membrane following a depolarizing pulse, as previously described for the crude venom. These toxins also caused repetitive firing of action potentials in single axons in response to 1 stimulating pulse, and spontaneous impulse firing. A 5th neurotoxin from C. sculpturatus venom had effects similar to those of the L. quinquestriatus toxins, slowing and preventing complete Na inactivation. The effect of this toxin was slowly removed during external perfusion by Ringer''s solution.