Common action of certain viruses, toxins, and activated complement: pore formation and its prevention by extracellular Ca2+.

Haemolysis by Sendai virus, alpha-toxin, and activated complement is inhibited by high concentrations of divalent cations. In Daudi cells, sublytic amounts of these agents induce the following changes: collapse of surface membrane potential, uptake of Na+ and loss of K+ from cells, and leakage of phosphorylated metabolites from cells. The changes induced by Sendai virus and complement are sensitive to physiological concentrations of extracellular Ca2+. It is concluded that fluctuations in plasma Ca2+ concentration may affect the damaging action of certain pore-forming agents on susceptible cells.