Abstract
Although superoxide anions are a well‐known mediator of cytotoxicity, their mechanism of target cell lysis is not clearly understood. In the present study we have used an exogenous source of superoxide to study erythrocyte cytolysis. RBC lysis was studied in buffers containing the cations Li^+^, Na^+^, K^+^, Rb^+^, and Cs^+^; superoxide anions were produced and available in these buffers. During this model superoxide‐dependent cytolytic process, erythrocytes underwent a shape change from biconcave disk to sphere as shown by scanning electron microscopy. Soret band transmitted light microscopy has confirmed this shape change and shown that it precedes cytosolic oxidation. This evidence is consistent with a colloid‐osmotic type lytic mechanism. Erythrocyte lysis was studied by ^51^Crrelease and light scattering methods. Superoxide‐mediated target cytolysis was characterized by: (1) a sigmoidal dose‐response curve and (2) a lag time in cytolysis after superoxide addition in kinetic light scattering experiments. The efficacy of cytolysis followed the rank order Cs^+^ > Rb^+^ > Na^+^, Li^+^ > sucrose = raffinose, which provides additional support for a colloid‐osmotic lytic mechanism. Furthermore, the rank order potency correlates with the cations' hydration numbers. We suggest that oxidative events trigger the formation of colloid‐osmotic pores ∼I nm in diameter. © 1993 Wiley‐Liss, Inc.