Apoptosis of Corneal Epithelial Cells Caused by Ultraviolet B-induced Loss of K⁺ is Inhibited by Ba²⁺

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• 作者：Courtney D. Glupker ; BS¹ ; Peter M. Boersma ; BS¹ ; ² ; Mark P. Schotanus ; BS¹ ; Loren D. Haarsma ; PhD² ; John L. Ubels ; PhD¹ ; ^{jubels@calvin.edu" class="auth_mail" title="E-mail the corresponding author}
• 关键词：apoptosis ; caspase ; corneal epithelium ; K+ channel ; potassium ; tears ; ultraviolet
• 刊名：The Ocular Surface
• 出版年：2016
• 出版时间：July 2016
• 年：2016
• 卷：14
• 期：3
• 页码：401-409
• 全文大小：1075 K

文摘

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 Ba²⁺ blocks several K⁺ channels, we tested whether Ba²⁺-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/cm². 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 Ba²⁺. K⁺ currents were activated in HCLE cells following UVB-exposure. These currents were reversibly blocked by 5 mM Ba²⁺. When HCLE cells were incubated with 5 mM Ba²⁺ 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 Ba²⁺ inhibits UVB-induced apoptosis by preventing loss of intracellular K⁺ when K⁺ channels are activated. Ba²⁺ 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.