Effects of divalent cations on snake venom cardiotoxin-induced hemolysis and 3H-deoxyglucose-6-phosphate release from human red blood cells.

At a low concentration of Naja naja kaouthia cardiotoxin (3 microM) Ca2+, Sr2+ and Ba2+ (2 mM), had little to no effect on 3H-deoxyglucose-6-phosphate (3H-dGlu-6-p) or hemoglobin release. At higher concentrations of N. n. kaouthia cardiotoxin (greater than or equal to 10 microM), Ca2+ (2 mM), but not Sr2+ or Ba2+, significantly enhanced 3H-dGlu-6-p and hemoglobin release. Mn2+ (2 mM) almost completely inhibited 3H-dGlu-6-p release and hemolysis at both the 3 microM and 10 microM concentrations of cardiotoxin. At a fixed concentration of N. n. kaouthia cardiotoxin (3 microM). Ca2+ at low concentrations (0.5 mM) enhanced 3H-dGlu-6-p and hemoglobin release, but at higher concentrations caused a dose-dependent inhibition of cardiotoxin action. The cardiotoxin from N. n. kaouthia venom (3 microM) induced 3H-dGlu-6-p release and hemolysis release with similar time courses and to similar extents. 3H-dGlu-6-p release induced by cardiotoxin was greatly enhanced as the pH of the medium was increased from 7.0 to 8.5. Similarities between 3H-dGlu-6-p and hemoglobin release do not support opening of pores in the plasmalemma of all red blood cells as the mode of action of cardiotoxins, but suggests that complete lysis of a subpopulation of cells occurs. Cardiotoxins have two components of lysis, only one of which is Ca2+-dependent. The Ca2+-dependent lysis is only evident at higher cardiotoxin concentrations and is likely due to trace phospholipase A2 contamination in the toxin fraction. Mn2+ is an effective antagonist of cardiotoxin action.