DYNAMICS OF PHOTOINDUCED CELL PLASMA-MEMBRANE INJURY

We have developed a video microscopy system designed for real-time mea surement of single cell damage during photolysis under well defined ph ysicochemical and photophysical conditions. Melanoma cells cultured in vitro were treated with the photosensitizer (PS), tin chlorin e6 (SnC e6) or immunoconjugate (SnCe6 conjugated to a anti-ICAM monoclonal ant ibody), and illuminated with a 10 mW He/Ne laser at a 630 nm wavelengt h. Cell membrane integrity was assessed using the vital dye calcein-AM . In experiments in which the laser power density and PS concentration were varied, it was determined that the time lag before cell rupture was inversely proportional to the estimated singlet oxygen flux to the cell surface. Microscopic examination of the lytic event indicated th at photo-induced lysis was caused by a point rupture of the plasma mem brane. The on-line nature of this microscopy system offers an opportun ity to monitor the dynamics of the cell damage process and to gain ins ights into the mechanism governing photolytic cell injury processes.