title: 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 microM 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 microM 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 microM 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.
authors.affiliation: Department of Biology, Calvin College, 3201 Burton St. SE, Grand Rapids, MI 49546, USA. jubels@calvin.edu
authors.forename: John L
authors.initials: JL
authors.lastname: Ubels
authors.forename: Mark P
authors.initials: MP
authors.lastname: Schotanus
authors.forename: Susan L
authors.initials: SL
authors.lastname: Bardolph
authors.forename: Loren D
authors.initials: LD
authors.lastname: Haarsma
authors.forename: Leah R
authors.initials: LR
authors.lastname: Koetje
authors.forename: Julienne R
authors.initials: JR
authors.lastname: Louters
mesh_terms: D017209:Apoptosis / Q000528:radiation effects*; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D061945:Caspase Inhibitors; D002452:Cell Count; D053938:DNA Fragmentation; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects; D019573:Epithelium, Corneal / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D020287:In Situ Nick-End Labeling; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D011802:Quinidine / Q000494:pharmacology; D051670:Shaw Potassium Channels / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; C492015:KCNC4 protein, human; D026902:Potassium Channel Blockers; D051670:Shaw Potassium Channels; D053148:Caspase 3; D053181:Caspase 8; D011802:Quinidine; D011188:Potassium