Effect of phospholipase A on actions of cobra venom cardiotoxins on erythrocytes and skeletal muscle.

The actions of two phospholipase-free cardiotoxins from the venom of the cobra Naja naja siamensis were compared to phospholipase-contaminated cardiotoxins in terms of their ability to lyse human erythrocytes and to depolarize and contract skeletal muscle. The presence of 3-5% (w/w) phospholipase caused a 20-30-fold increase in the haemolytic activity of the two cardiotoxins, the pure cardiotoxins being virtually without haemolytic activity at 10(-7)-10(-6) M. Phospholipase contamination did not enhance the ability of the cardiotoxins to cause contracture of chick biventer cervicis muscles and it caused less than a 2-fold increase in the depolarizing activity of the cardiotoxins on cultured skeletal muscle. Phospholipase-free cardiotoxins were about 10-20 times more active on cultured skeletal muscle fibres than on erythrocytes. These results support the hypothesis that some cardiotoxins have more affinity for the membranes of excitable cells than for those of other cells such as erythrocytes.