Adelwoehrer N E, Mahnert W
Department of Gynecology and Obstetrics, University of Graz, Austria.
Arch Gynecol Obstet. 1993;252(4):179-84. doi: 10.1007/BF02426355.
Hexoprenaline is a beta-adrenergic agent used for tocolysis after the 26th week of pregnancy. The purpose of the present study was to demonstrate the site of action of hexoprenaline on the membrane of single isolated smooth muscle cells. The main action of beta-mimetics on the cell is hyperpolarization of the cellular membrane, i.e. beta-mimetics have similar effects as K(+)-ions (Standen et al., 1989). Our results indicate a prolonged and significantly enhanced activity of K(+)-channels in the cell membrane, as may also be demonstrated by the use of the K(+)-channel activator Calcitonin-gene related peptide (CGRP). In control experiments under physiological conditions, we observed a large conductance K(+)-channel with 158 pS. The channel was voltage dependent and Ca++ sensitive indicating that it belongs to the class of big conductance Ca(++)-activated K(+)-channels (BKCa). Hexoprenaline and CGRP both increased the open probability (P(o)) of the channel measured with the patch clamp system in the cell attached configuration. Hexoprenaline was also an activator of the BKCa in the presence of Nitrendipine, indicating that the activation of the Ca++ sensitive channel is not an indirect effect of Ca++ currents via L-type Ca++ channels.
己双肾上腺素是一种β-肾上腺素能药物，用于妊娠26周后的安胎治疗。本研究的目的是证明己双肾上腺素在单个分离的平滑肌细胞膜上的作用位点。β-拟似剂对细胞的主要作用是使细胞膜超极化，即β-拟似剂具有与K⁺离子类似的作用（斯坦登等人，1989年）。我们的结果表明细胞膜中K⁺通道的活性延长且显著增强，使用K⁺通道激活剂降钙素基因相关肽（CGRP）也可证明这一点。在生理条件下的对照实验中，我们观察到一个电导为158 pS的大电导K⁺通道。该通道具有电压依赖性且对Ca²⁺敏感，表明它属于大电导Ca²⁺激活K⁺通道（BKCa）类别。己双肾上腺素和CGRP均增加了在细胞贴附式配置下用膜片钳系统测量的该通道的开放概率（Pₒ）。在尼群地平存在的情况下，己双肾上腺素也是BKCa的激活剂，这表明Ca²⁺敏感通道的激活不是通过L型Ca²⁺通道的Ca²⁺电流的间接作用。
