UV-induced corneal epithelial cell death by activation of potassium channels.
OBJECTIVE
The purpose of the present study is to determine the role of K+ channel activity as an early event in UV-induced corneal epithelial cell apoptosis.


METHODS
Both cell-attached and nystatin-perforated patch-clamping were performed to record K+ channel activity in rabbit corneal epithelial (RCE) and primary cultured rabbit corneal epithelial (PRCE) cells exposed to UV irradiation. On exposure of corneal epithelial cells or intact corneas to UV-C irradiation or treatment of corneal epithelial cells with etoposide, cell apoptosis was determined by DNA fragmentation, ethidium bromide-acridine orange nuclear stain and TdT-mediated dUTP nick-end labeling (TUNEL).


RESULTS
In the present study, UV-irradiation-induced corneal epithelial cell apoptosis through activation of a K+ channel in the cell membrane was an early event in response to UV irradiation. UV-C irradiation (42 microJ/cm(2)) activated robust K+ channel activity in RCE and PRCE cells at both the single-channel and whole-cell levels, when measured with the cell-attached and nystatin-perforated patch clamps, respectively. Suppression of UV-irradiation-induced K+ channel activity with the specific K+ channel blocker 4-aminopurydine (4-AP) prevented UV-irradiation-induced apoptosis in the RCE and PRCE cells, loss of the superficial layer of corneal epithelium, and apoptosis in the basal layer corneal epithelium. However, suppression of K+ channel activity did not protect RCE and PRCE cells from etoposide, a topoisomerase II inhibitor, which induced cell death by bypassing the membrane. Furthermore, application of valinomycin, a K+ ionophore, to mimic the effect of mass activation of the K+ channel in RCE and PRCE cells caused cell apoptosis.


CONCLUSIONS
The results indicate that UV irradiation induces superactivity of K+ channels in the membrane is an early event mediating signaling transduction and resulting in corneal epithelial cell death in response to UV irradiation.
Wang
Ling
L
Division of Molecular Medicine, Harbor-UCLA Medical Center, UCLA School of Medicine, University of California-Los Angeles, 1124 W. Carson Street, Torrance, CA 90502, USA.
Li
Tie
T
Lu
Luo
L
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects*; D002461:Cell Line, Transformed; D002472:Cell Transformation, Viral; D019573:Epithelium, Corneal / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D020287:In Situ Nick-End Labeling; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits; D013539:Simian virus 40; D059005:Topoisomerase II Inhibitors; D014466:Ultraviolet Rays; D014634:Valinomycin / Q000494:pharmacology
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D059005:Topoisomerase II Inhibitors; D014634:Valinomycin; D005047:Etoposide; D015761:4-Aminopyridine