Inhibition of UV-B induced apoptosis in corneal epithelial cells by potassium channel modulators

Abstract

The goal of this study was to determine whether prevention of K + loss can protect human corneal-limbal epithelial (HCLE) cells from UV-B induced apoptosis. Immunostaining for activated caspase-3 of HCLE cells exposed to 150–200 mJ/cm 2 UV-B demonstrated induction of apoptosis 6 h after exposure. The number of apoptotic cells was decreased by incubation in medium with 25 or 100 mM K +. If this protection is due to a reduction of UV-induced K + loss then K + channel blockers should also protect HCLE cells from UV-B. Caspase-8 activity induced by exposure to UV-B at 150 mJ/cm 2 was significantly reduced when the cells were incubated in 0.3 μM BDS-I or 0.05–1 mM quinidine. Caspase-3 was also activated by UV-B and a reduction in activity was observed after incubation in 0.1–0.3 μM BDS-I and 0.1–1 mM quinidine. Induction of DNA fragmentation, as measured by the TUNEL assay, was decreased by treatment with 0.3 μM BDS-I and 0.01–0.05 mM quinidine. Patch-clamp recording showed activation of K + channels after exposure to UV-B and a decrease in outward K + current was observed following application of BDS-I. Quinidine did not block K + currents in HCLE cells, suggesting that the protective effect of quinidine occurs by a mechanism other than via K + channels. The effect of the K + channel blocker BDS-1 on HCLE cells exposed to UV-B confirms that preventing K + efflux protects corneal epithelial cells from apoptosis. This suggests the elevated [K +] in tears may protect the corneal epithelium from effects of ambient UV-B.