Groschner K, Silberberg S D, Gelband C H, van Breemen C
University of Miami, School of Medicine, Department of Molecular and Cellular Pharmacology, FL 33101.
Pflugers Arch. 1991 Jan;417(5):517-22. doi: 10.1007/BF00370948.
Large-conductance Ca2(+)-activated K+ channels were studied in membranes of cultured rabbit airway smooth muscle cells, using the patch-clamp technique. In cell-attached recordings, channel openings were rare and occurred only at very positive potentials. Bradykinin (10 microM), an agonist which releases Ca2+ from the sarcoplasmic reticulum, transiently increased channel activity. The metabolic blocker 2,4-dinitrophenol (20 microM), which lowers cellular adenosine triphosphate (ATP) levels, induced a sustained increase of channel activity in cell-attached patches. In excised patches, these channels had a slope conductance of 155 pS at 0 mV, were activated by depolarization and by increasing the Ca2+ concentration at the cytoplasmic side above 10(-7) mol/l. ATP, applied to the cytoplasmic side of the patches, dose-dependently decreased the channel's open-state probability. An inhibition constant (Ki) of 0.2 mmol/l was found for the ATP-induced inhibition. ATP reduced the Ca2+ sensitivity of the channel, shifting the Ca2+ activation curve to the right and additionally reducing its steepness. Our results demonstrate that cytoplasmic ATP inhibits a large-conductance Ca2(+)-activated K+ channel in airway smooth muscle. This ATP modulation of Ca2(+)-activated K+ channels might serve as an important mechanism linking energy status and the contractile state of the cells.
利用膜片钳技术，对培养的兔气道平滑肌细胞膜中的大电导钙激活钾通道进行了研究。在细胞贴附式记录中，通道开放很少见，且仅在非常正的电位时出现。缓激肽（10微摩尔），一种从肌浆网释放钙离子的激动剂，可短暂增加通道活性。代谢阻滞剂2,4-二硝基苯酚（20微摩尔），可降低细胞内三磷酸腺苷（ATP）水平，在细胞贴附式膜片中可诱导通道活性持续增加。在切除的膜片中，这些通道在0毫伏时的斜率电导为155皮安，可被去极化以及将胞质侧钙离子浓度提高到10^(-7)摩尔/升以上所激活。施加于膜片胞质侧的ATP，可剂量依赖性地降低通道的开放概率。发现ATP诱导抑制的抑制常数（Ki）为0.2毫摩尔/升。ATP降低了通道的钙敏感性，使钙激活曲线右移，并额外降低了其陡峭度。我们的结果表明，胞质ATP抑制气道平滑肌中的大电导钙激活钾通道。这种ATP对钙激活钾通道的调节可能是连接能量状态和细胞收缩状态的重要机制。
