THE EFFECT OF BRIEF ILLUMINATION ON INTRACELLULAR FREE CALCIUM-CONCENTRATION IN CELLS WITH 5-AMINOLEVULINIC ACID-INDUCED PROTOPORPHYRIN-IX SYNTHESIS

The effect of illumination on intracellular free calcium concentration , [Ca2+](i), was studied in a cell line (WiDr cells) derived from a pr imary adenocarcinoma of the rectosigmoid colon. In these cells the bio synthesis of protoporphyrin IX was stimulated by 5-aminolevulinic acid to reach levels of 600-700 pmol of protoporphyrin IX per mg cell prot ein. A brief (1-min) exposure of the cells to light (70% of light ener gy at 340-380 nm) resulted in an increase in [Ca2+](i). This increase was not reversible over a period of at least 20 min following illumina tion. Elevation of [Ca2+](i) most probably represented an influx of ca lcium ions from the medium to the cell, since it was completely abolis hed in the presence of extracellular EGTA. The increased [Ca2+](i) did not reflect general membrane damage, as determined by trypan blue sta ining as well as measurement of the intercalation of ethidium bromide into cellular DNA, and neither did the sustained elevation of [Ca2+](i ) lead to any substantial loss of clonogenicity following illumination of protoporphyrin-containing cells. Together these results indicate t hat an increased [Ca2+](i) level is not per se a cause of cell death d uring photodynamic therapy.