Hurley B R, Preiksaitis H G, Sims S M
Department of Physiology, University of Western Ontario, Canada.
Am J Physiol. 1999 Apr;276(4):G843-52. doi: 10.1152/ajpgi.1999.276.4.G843.
We examined the properties of K+ channels in smooth muscle cells dissociated from human esophagus using patch-clamp recording in the cell-attached configuration. The predominant channel observed had a conductance of 224 +/- 4 pS, and current reversal was dependent on K+ concentration. Channel activity was voltage dependent and increased with elevation of intracellular free Ca2+ concentration ([Ca2+]i), consistent with this being the large-conductance Ca2+-dependent K+ (KCa) channel. ACh as well as caffeine caused transient increases in KCa channel activity, and the effects of ACh persisted in Ca2+-free solution, indicating that Ca2+ release from stores contributed to channel activation. Simultaneous patch clamp and fluorescence revealed that KCa channel activity was well correlated with elevation of [Ca2+]i. The functional role of KCa channels in esophagus was studied by measuring ACh-induced contraction of strips of muscle. Tetraethylammonium and iberiotoxin, blockers of KCa channels, increased ACh-induced contraction, consistent with a role for K+ channels in limiting excitation and contraction. These studies are the first to characterize KCa channels and their regulation in human esophageal smooth muscle.
我们采用细胞贴附式膜片钳记录技术，研究了从人食管分离出的平滑肌细胞中钾离子通道的特性。观察到的主要通道电导为224±4 pS，电流反转取决于钾离子浓度。通道活性依赖电压，并随细胞内游离钙离子浓度（[Ca2+]i）升高而增强，这与该通道为大电导钙依赖性钾离子（KCa）通道一致。乙酰胆碱（ACh）以及咖啡因可使KCa通道活性短暂增强，且ACh的作用在无钙溶液中依然存在，这表明从储存库释放的钙离子参与了通道激活。同时进行膜片钳记录和荧光检测发现，KCa通道活性与[Ca2+]i升高密切相关。通过测量ACh诱导的肌条收缩，研究了KCa通道在食管中的功能作用。KCa通道阻滞剂四乙铵和iberiotoxin可增强ACh诱导的收缩，这与钾离子通道在限制兴奋和收缩方面的作用相符。这些研究首次对人食管平滑肌中的KCa通道及其调节进行了表征。
