NEAR-VISIBLE ULTRAVIOLET-LIGHT INDUCES A NOVEL UBIQUITOUS CALCIUM-PERMEABLE CATION CURRENT IN MAMMALIAN-CELL LINES

1. We studied the immediate and short-term effects of UV light in the near-visible range at the cellular and membrane level using the whole- cell patch-damp technique in combination with digital fluorescence ima ging. 2. Illumination with monochromatic UVA light (340-380 nm) induce d a sustained nonsaturable increase in membrane conductance dependent on wavelength and light intensity in several different mammalian cell types including RBL, mast, HEK, PC12 and 3T3 cells. 3. The current was non-selective for cations and permeable to Ca2+, but was inhibited by trivalent cations and was not due to the activation of an endogenous ion channel. We termed this novel current I-LiNC for light-induced non -selective cation current. 4. A similar current was evoked by chemical peroxidants such as hydrogen peroxide and tertbutylhydroperoxide, but not by cytosolic oxidized glutathione. 5. The free-radical scavengers tocopherol (vitamin E) and ascorbic acid (vitamin C) significantly re duced the UV light effect. 6. The generation of the current was membra ne delimited since it could be induced by the same UVA treatment in ce ll-free membrane patches showing a similar wavelength dependence. 7. T hese results suggest that I-LiNC is activated by UVA light-induced gen eration of free radicals acting through lipid or protein peroxidation, and may represent a ubiquitous mechanism by which Na+ and Ca2+ can en ter cells after phototoxic or free radical-induced membrane damage.