Activation of a Ca2+-dependent cation conductance with properties of TRPM2 by reactive oxygen species in lens epithelial cells

Ion channels are crucial for maintenance of ion homeostasis and transparency of the lens. The lens epithelium is the metabolically and electrophysiologically active cell type providing nutrients, ions and water to the lens fiber cells. Ca2+-dependent non-selective ion channels seem to play an important role for ion homeostasis. The aim of the study was to identify and characterize Ca2+- and reactive oxygen species (ROS)-dependent non-selective cation channels in human lens epithelial cells. RT-PCR revealed gene expression of the Ca2+-activated non-selective cation channels TRPC3, TRPM2, TRPM4 and Ano6 in both primary lens epithelial cells and the cell line HLE-B3, whereas TRPM5 mRNA was only found in HLE-B3 cells. Using whole-cell patch-clamp technique, ionomycin evoked non-selective cation currents with linear current-voltage relationship in both cell types. The current was decreased by flufenamic acid (FFA), 2-APB, 9-phenanthrol and miconazole, but insensitive to DIDS, ruthenium red, and intracellularly applied spermine. H2O2 evoked a comparable current, abolished by FFA. TRPM2 protein expression in HLE-B3 cells was confirmed by means of immunocytochemistry and western blot. In summary, we conclude that lens epithelial cells functionally express Ca2+- and H2O2-activated non-selective cation channels with properties of TRPM2.