title: Apoptosis of Corneal Epithelial Cells Caused by Ultraviolet B-induced Loss of K(+) is Inhibited by Ba(2.).
abstract: UVB exposure at ambient outdoor levels triggers rapid K(+) loss and apoptosis in human corneal limbal epithelial (HCLE) cells cultured in medium containing 5.5 mM K(+), but considerably less apoptosis occurs when the medium contains the high K(+) concentration that is present in tears (25 mM). Since Ba(2+) blocks several K(+) channels, we tested whether Ba(2+)-sensitive K(+) channels are responsible for some or all of the UVB-activated K(+) loss and subsequent activation of the caspase cascade and apoptosis. Corneal epithelial cells in culture were exposed to UVB at 80 or 150 mJ/cm(2). Patch-clamp recording was used to measure UVB-induced K(+) currents. Caspase-activity and TUNEL assays were performed on HCLE cells exposed to UVB followed by incubation in the presence or absence of Ba(2+). K(+) currents were activated in HCLE cells following UVB-exposure. These currents were reversibly blocked by 5 mM Ba(2+). When HCLE cells were incubated with 5 mM Ba(2+) after exposure to UVB, activation of caspases-9, -8, and -3 and DNA fragmentation were significantly decreased. The data confirm that UVB-induced K(+) current activation and loss of intracellular K(+) leads to activation of the caspase cascade and apoptosis. Extracellular Ba(2+) inhibits UVB-induced apoptosis by preventing loss of intracellular K(+) when K(+) channels are activated. Ba(2+) therefore has effects similar to elevated extracellular K(+) in protecting HCLE cells from UVB-induced apoptosis. This supports our overall hypothesis that elevated K(+) in tears contributes to protection of the corneal epithelium from adverse effects of ambient outdoor UVB.
authors.affiliation: Department of Biology, Calvin College, Grand Rapids, MI, USA.
authors.forename: Courtney D
authors.initials: CD
authors.lastname: Glupker
authors.affiliation: Department of Biology, Calvin College, Grand Rapids, MI, USA; Department of Physics, Calvin College, Grand Rapids, MI, USA.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Boersma
authors.affiliation: Department of Biology, Calvin College, Grand Rapids, MI, USA.
authors.forename: Mark P
authors.initials: MP
authors.lastname: Schotanus
authors.affiliation: Department of Physics, Calvin College, Grand Rapids, MI, USA.
authors.forename: Loren D
authors.initials: LD
authors.lastname: Haarsma
authors.affiliation: Department of Biology, Calvin College, Grand Rapids, MI, USA. Electronic address: jubels@calvin.edu.
authors.forename: John L
authors.initials: JL
authors.lastname: Ubels
mesh_terms: D017209:Apoptosis; D020169:Caspases; D003315:Cornea; D004847:Epithelial Cells; D006801:Humans; D020287:In Situ Nick-End Labeling; D014466:Ultraviolet Rays
chemical_list: D020169:Caspases
keywords: K(+) channel; apoptosis; caspase; corneal epithelium; potassium; tears; ultraviolet