Plasma membrane depolarization and calcium influx during cell injury by photodynamic action.

The plasma membrane has been implicated as one of the critical targets of photodynamic action. We observed that plasma membrane depolarization is an early event in the photodynamic action of zinc phthalocyanine disulfonate in mouse myeloma cells, showing both photosensitizer concentration and light dose dependence. The depolarization was observed immediately upon exposure to light, while membrane integrity was retained and showed a strong correlation with cell killing. In this study the use of channel blockers and alteration of ion concentration was employed to determine the factors involved in the membrane depolarization process. A general rise in cation permeability is associated with the depolarization. Loss of intracellular potassium was detected and an increase in intracellular free calcium was also observed. Sodium was found to strongly influence the photosensitized depolarization.