INHIBITION OF DIPHOSPHATIDYLGLYCEROL SYNTHESIS BY UV A-RADIATIONS IN NCTC 2544 HUMAN KERATINOCYTES

The effects of u.v. A radiations on phospholipid synthesis were studied in the N.C.T.C. 2544 human keratinocyte cell line, by using [C-14]arachidonic acid, [C-14]oleic acid or sodium [P-32]- orthophosphate as precursors, Cells were irradiated in Hanks' medium with 365 nm light at doses up to 19 J/cm(2), and then phospholipid synthesis from the three precursors was studied. Under these conditions, only small alterations in the incorporation pattern of [C-14]arachidonic into phospholipids [phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI)] were observed, for u.v. A irradiation doses up to 19J/cm(2). In contrast, with [C-14]oleic acid as precursor, two additional spots were observed, which co-migrate with pure phosphatidylglycerol (PG) and diphosphatidylglycerol (DPG) standards. The incorporation of [C-14]oleic acid into PG and DPG was decreased in a dose-dependent manner after u.v. A exposure, with about 50% and 75% decreases at 9.5 J/cm(2) and 19 J/cm(2) respectively. As for arachidonic acid incorporation, no significant differences in the synthesis of the major phospholipids (PC, PE, PI) were noted upon u.v. A exposure. The dramatic and selective decrease in PG and DPG syntheses was confirmed with [P-32]orthophosphate as precursor. As DPG is a specific component of the mitochondrial inner membrane, it appears that one of the early kinds of damage induced by u.v. A irradiation could be the impairment of mitochondrial functions.