UVB irradiation induces changes in the distribution and release of 14C-arachidonic acid in human keratinocytes in culture.

Following labeling of human keratinocytes in culture for 48 h with 14C-arachidonic acid (800,000 cpm), 86.8 +/- 0.5% (mean +/- SEM) of the radioactivity was incorporated into the cells. Two hours after exposure to UVB irradiation at doses up to 392 mJ/cm2 of erythemally effective (EE) UVB irradiation, only slight changes in the distribution of arachidonic acid could be detected. However, 24 h after irradiation the release of arachidonic acid into the culture medium was significantly increased. The distribution of arachidonic acid was also changed: there was a considerable loss in the amount of radioactivity associated with phosphatidylethanolamine. With doses up to 174 mJ/cm2 (EE) of UVB, the decrease in the labeling of phospholipids was accompanied by an increased arachidonic acid content in the nonphosphorus lipids, especially in the triacylglycerols. Following a high dose of UVB (392 mJ/cm2, EE), a substantial release of label was detected, but the labeling of triacylglycerols was unaltered. The present study suggests that in human keratinocytes UVB irradiation induces the release of arachidonic acid from the cellular lipids and that the major source of the released arachidonic acid is phosphatidylethanolamine.