Near‐visible ultraviolet light induces a novel ubiquitous calcium‐permeable cation current in mammalian cell lines

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Abstract
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‐clamp technique in combination with digital fluorescence imaging. Illumination with monochromatic UVA light (340‐380 nm) induced a sustained non‐saturable increase in membrane conductance dependent on wavelength and light intensity in several different mammalian cell types including RBL, mast, HEK, PC12 and 3T3 cells. 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 ILiNC for light‐induced non‐selective cation current. A similar current was evoked by chemical peroxidants such as hydrogen peroxide and tert‐butylhydroperoxide, but not by cytosolic oxidized glutathione. The free‐radical scavengers tocopherol (vitamin E) and ascorbic acid (vitamin C) significantly reduced the UV light effect. The generation of the current was membrane delimited since it could be induced by the same UVA treatment in cell‐free membrane patches showing a similar wavelength dependence. These results suggest that ILiNC is activated by UVA light‐induced generation of free radicals acting through lipid or protein peroxidation, and may represent a ubiquitous mechanism by which Na+ and Ca2+ can enter cells after phototoxic or free radical‐induced membrane damage.