The cytolytic effect of cobra cardiotoxin on Ehrlich ascites tumor cells and its inhibition by Ca2+.

In the presence of cobra cardiotoxin, cellular constituents from Ehrlich ascites tumor cells leak out into the medium. The leakage is detrimental to important cell functions. The rate of cardiotoxininduced cytolysis is dose-dependent and is not affected by cell concentration. Calcium ion inhibits the cytolysis reversibly; addition of calcium ion stops the cytolytic action whereas removal of calcium ion by EDTA abolishes the the inhibitory effect. Among the alkaline earth metals studied, Ca2+, Sr2+ and Ba2+ inhibit whereas Mg2+ potentiates the cytolysis. Progression of cytolysis requires a continuous presence of cardiotoxin; removal of cardiotoxin molecules by cardiotoxin antiserum completely abolishes the cytolytic activity. The ability of calcium ion to inhibit cardiotoxin-induced cytolysis is probably due to an interference of the binding of cardiotoxin molecules to the cell membrane.