ULTRAVIOLET RADIATION-INDUCED PHOSPHOLIPASE-A2 ACTIVATION OCCURS IN MAMMALIAN-CELL MEMBRANE PREPARATIONS

Ultraviolet erythema in human skin is mediated in part by membrane derivatives of arachidonic acid (AA). UVA (320-400 nm) and UVB (290-320 nm) have been shown to induce release of AA from intact mammalian cells in culture. In order to investigate the mechanism of this release we examined the effect of UVA and UVB on release of [H-3] AA from membrane preparations of murine fibroblasts. C3H 10T1/2 cells Were prelabelled for 24 h with [H-3] AA. The membrane fractions of the cells were separated after lysis by differential centrifugation. The membranes were irradiated in suspension and the [H-3] AA released from the membranes was determined by scintillation spectroscopy of supernatants 3-4 h after irradiation. Both UVA and UVB induced release of AA from the membrane preparations. The response to UVB was small but significant, reaching levels approximately 150% of control release at doses of 1,200-4,000 J/m2. The response to UVA was larger; doses of 2.5-5.0 J/cm2 induced release equal to twice control (200%) levels, while doses of 10-20 J/cm2 induced maximal release at levels approximately 400% of control. Time course studies with UVB and UVA showed maximal release at 4 h after irradiation. When the membrane preparations were incubated with a polyclonal anti-phospholipase A2 antibody the UV induced release of [H-3] AA was completely inhibited in both UVB (1200 J/m2) and UVA (10 J/cm2) treated cells. These data suggest that activation of phospholipase A2 is responsible for the UV induced release of AA in mammalian cells and that the mechanism of this activation is due, in part at least, to direct photon-membrane interaction.