CA2-ACTION IN HUMAN CEREBRAL GLIOMA (U-87 MG) CELLS - POSSIBLE INVOLVEMENT OF A CALCIUM-CHANNEL( INFLUX INDUCED BY PHOTODYNAMIC)

The plasma membrane has been implicated as a critical target of photod ynamic action on cells. We have observed that the photosensitization o f human cerebral glioma (U-87 MG) cells by hematoporphyrin derivative (HpD) causes a large increase in intracellular calcium [Ca2+](i). This increase in [Ca2+](i) was solely due to the influx of extracellular C a2+ through the plasma membrane and showed a dependence on HpD concent ration, light dose and concentration of calcium in the extracellular m edium. The magnitude of the Ca2+ influx decreased with increasing post irradiation time, which suggests that the cell membrane partially reco vers from the photodynamic injury. The photoinduced Ca2+ influx was in hibited by the Ca2+ channel blocker diltiazem and the reducing agent d ithioerythritol. These findings are discussed in terms of possible act ivation of a Ca2+ channel as a result of photosensitization.