ABSTRACT Illumination of GH3 cells in the presence of uroporphyrin produced an increase in membrane permeability measured by patch clamp electrophysiology and designated ILEAK. The production of ILEAK was shown to be dependent on uroporphyrin concentration, intensity of illumination and duration of illumination. Reciprocity between illumination intensity and duration was shown to hold over a restricted range, such that the amount of ILEAK was dependent, to a first approximation, on the total number of incident photons. Either ascorbate (≥0.1 mM) or butylated hydroxytoluene (BHT) (≥2 µM) was capable of inhibiting the production of ILEAK. The reversal potential of ILEAK was about –10 mV before illumination and became more positive during illumination, reaching a plateau near 0 mV or slightly positive to 0 mV. BHT or ascorbate did not significantly alter the change in reversal potential, although a small effect of these antioxidants on the value before illumination cannot be excluded. The current-voltage plots of ILEAK were linear. This linearity and the reversal potential data suggest that ILEAK flows through a relatively nonselective ionic pathway.
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