The objective of this investigation was to gain a deeper understanding
of the intracellular events that precede photolysis of cells. A model
system, consisting of malignant melanoma cells pretreated,vith the ca
lcium sensitive fluorescent dye, Fluo-3, was used to examine the intra
cellular calcium dynamics in single-cell photolysis experiments. Expos
ure of the cells to 632 nm laser light in the presence of photosensiti
zer, tin chlorin e6, resulted in a rise in intracellular calcium. The
increase in intracellular calcium,was blocked using a variety of calci
um channel blocking agents, including verapamil, nifedipine, and nicke
l. Treatment with the channel blockers was also effective in either de
creasing or eliminating cell death despite the presence of lethal dose
s of photosensitizer and irradiation. These results show that intracel
lular calcium rises prior to plasma membrane lysis, and that this earl
y rise in intracellular calcium is necessary for membrane rupture.