Detweiler Neil D, Song Li, McClenahan Samantha J, Versluis Rachel J, Kharade Sujay V, Kurten Richard C, Rhee Sung W, Rusch Nancy J
Department of Pharmacology and Toxicology, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA.
Department of Anesthesiology, School of Medicine, Vanderbilt University, Nashville, Tennessee, USA.
Pulm Circ. 2016 Dec;6(4):563-575. doi: 10.1086/688838.
A loss of K efflux in pulmonary arterial smooth muscle cells (PASMCs) contributes to abnormal vasoconstriction and PASMC proliferation during pulmonary hypertension (PH). Activation of high-conductance Ca-activated (BK) channels represents a therapeutic strategy to restore K efflux to the affected PASMCs. However, the properties of BK channels in PASMCs-including sensitivity to BK channel openers (BKCOs)-are poorly defined. The goal of this study was to compare the properties of BK channels between PASMCs of normoxic (N) and chronic hypoxic (CH) rats and then explore key findings in human PASMCs. Polymerase chain reaction results revealed that 94.3% of transcripts encoding BKα pore proteins in PASMCs from N rats represent splice variants lacking the stress axis regulated exon insert, which confers oxygen sensitivity. Subsequent patch-clamp recordings from inside-out (I-O) patches confirmed a dense population of BK channels insensitive to hypoxia. The BK channels were highly activated by intracellular Ca and the BKCO lithocholate; these responses require BKα-β subunit coupling. PASMCs of CH rats with established PH exhibited a profound overabundance of the dominant oxygen-insensitive BKα variant. Importantly, human BK (hBK) channels in PASMCs from human donor lungs also represented the oxygen-insensitive BKα variant activated by BKCOs. The hBK channels showed significantly enhanced Ca sensitivity compared with rat BK channels. We conclude that rat BK and hBK channels in PASMCs are oxygen-insensitive BKα-β complexes highly sensitive to Ca and the BKCO lithocholate. BK channels are overexpressed in PASMCs of a rat model of PH and may provide an abundant target for BKCOs designed to restore K efflux.
肺动脉平滑肌细胞（PASMCs）中钾离子外流的丧失会导致肺动脉高压（PH）期间异常的血管收缩和PASMC增殖。激活高电导钙激活（BK）通道是恢复受影响PASMCs钾离子外流的一种治疗策略。然而，PASMCs中BK通道的特性，包括对BK通道开放剂（BKCOs）的敏感性，目前尚不清楚。本研究的目的是比较常氧（N）大鼠和慢性缺氧（CH）大鼠PASMCs中BK通道的特性，然后在人PASMCs中探索关键发现。聚合酶链反应结果显示，N大鼠PASMCs中编码BKα孔蛋白的转录本中有94.3%代表缺乏应激轴调节外显子插入的剪接变体，该插入赋予氧敏感性。随后从内向外（I-O）膜片进行的膜片钳记录证实了大量对缺氧不敏感的BK通道。BK通道被细胞内钙和BKCO石胆酸高度激活；这些反应需要BKα-β亚基偶联。已建立PH的CH大鼠的PASMCs表现出占主导地位的氧不敏感BKα变体的大量过剩。重要的是，来自人类供体肺的PASMCs中的人BK（hBK）通道也代表被BKCOs激活的氧不敏感BKα变体。与大鼠BK通道相比，hBK通道显示出显著增强的钙敏感性。我们得出结论，PASMCs中的大鼠BK和hBK通道是对钙和BKCO石胆酸高度敏感的氧不敏感BKα-β复合物。BK通道在PH大鼠模型的PASMCs中过表达，可能为旨在恢复钾离子外流的BKCOs提供丰富的靶点。
