KINETICS OF PORPHYRIN ACCUMULATION IN CULTURED EPITHELIAL-CELLS EXPOSED TO ALA

1. The kinetics of porphyrin accumulation in cultured mammalian epithe lial cells (CNCM-I-221) during exposure to ALA was investigated. 2. Th e total porphyrin synthesized is a function of ALA concentration and t he incubation time. The cellular porphyrin content exhibited a saturat ion pattern, reaching a plateau at about 0.04 fmol porphyrins/cell. A biphasic time-dependent increase in the total porphyrin synthesized wa s observed. 3. After 3 hr of exposure to ALA the rate of synthesis inc reased to almost twice the initial rate, reaching between 0.02 and 0.0 5 fmol porphyrins/cell/hr depending on serum concentration in the medi um. 4. Two effects of FBS on ALA-stimulated porphyrin accumulation wer e observed. Greater total porphyrin synthesis was found when incubatio ns were made in 10% FBS compared to those in 1% FBS. 5. The higher ser um concentration also caused a greater release into the medium of the porphyrins generated in the cells with a calculated half-life of 24 mi n in 10% serum-supplemented medium compared with 62 min in 1% serum. 6 . The results obtained from cell synchronization experiments suggest t hat there is little obvious cell cycle-dependent variation in the synt hesis of porphyrins from ALA. 7. The small differences in the intracel lular porphyrin content that were observed may be attributed to a slig ht reduction in the rate of loss of porphyrins in G2/M cells.