氨茶碱对藤壶肌纤维钠外流的作用方式。

Mode of action of theophylline on sodium efflux in barnacle muscle fibers.

作者信息

Bittar E E, Benjamin H

出版信息

J Membr Biol. 1978 Feb 6;39(1):57-73. doi: 10.1007/BF01872755.

PMID:204785

Abstract

The response of the Na efflux in unpoisoned barnacle fibers to 10 mM theophylline is biphasic; i.e., inhibition is followed by stimulation. The stimulatory response is unaffected by ouabain. Fibers pretreated with ouabain show no transitory inhibition when 10 mM theophylline is applied, but show prompt stimulation the magnitude of which is comparable to that observed with unpoisoned fibers. The same holds true for lower concentrations of theophylline. Prior injection of 500 mM EGTA completely abolishes the biphasic action of 10 mM theophylline. External application of 10 mM theophylline following removal of external Ca2+ fails to bring about a biphasic effect. Ca2+ restoration, however, results in a moderate rise in the Na efflux. External application of 10 mM theophylline stimulates the Na efflux into Ca2+-free artificial seawater (ASW) when the test fibers are pretreated with ouabain. Injection of the protein inhibitor of Walsh leads to reduced stimulation by 10 mM theophylline of the Na efflux in unpoisoned fibers. Injection of the protein inhibitor of Corbin into unpoisoned fibers leads to reduced stimulation by 10 mM theophylline. Injection of cAMP into ouabain-poisoned fibers, following internal application of Corbin's inhibitor and external application of 10 mM theophylline, fails to cause a marked rise in the ouabain-insensitive Na efflux. Injection of Corbin's inhibitor into ouabain-poisoned fibers, following the onset of peak stimulation by 10 mM theophylline, fails to reduce the Na efflux. Fibers injected with 1 mM and 100 mM EGTA and exposed to 10 mM theophylline show a marked reduction in the response of the ouabain-insensitive Na efflux to injected cAMP when the concentration of theophylline is 10 mM. A poor response to injected cAMP is also seen in fibers bathed in Ca-free ASW containing 10 mM theophylline. Theophylline (10 mM) fails to cause an enhanced stimulation of the ouabain-insensitive Na efflux into Ca-free 3 mM-HEPES ASW or 10 mM-Ca2+ -3mM-HEPES ASW following the addition of protons to the bathing medium. An enhanced response is similarly not observed with injected cAMP following the addition of theophylline to the bathing medium. Injection of 8-fluorotheophylline, 3-isobutyl-1-methylxanthine and doxantrazole leads to a marked reduction in the response of the ouabain-insensitive Na efflux to injected cAMP. Contraction always takes place upon injecting these substances. These results are in keeping with the theory that theophylline acts chiefly by reducing myoplasmic pCa(pCa=-log10[Ca2+]), and that a reduced pCa leads to stimulation of the ouabain-insensitive Na efflux as the result of activation of the cGMP-dependent protein kinase system by newly formed cGMP.

摘要

在未中毒的藤壶纤维中，10 mM 茶碱对钠外流的反应是双相的，即先是抑制，随后是刺激。刺激反应不受哇巴因的影响。用哇巴因预处理的纤维在施加 10 mM 茶碱时没有短暂抑制，但会迅速产生刺激，其幅度与未中毒纤维中观察到的相当。较低浓度的茶碱也是如此。预先注射 500 mM EGTA 可完全消除 10 mM 茶碱的双相作用。去除细胞外 Ca2+ 后施加 10 mM 茶碱未能产生双相效应。然而，恢复 Ca2+ 会导致钠外流适度增加。当测试纤维用哇巴因预处理时，在无 Ca2+ 的人工海水中施加 10 mM 茶碱会刺激钠外流。注射 Walsh 的蛋白抑制剂会导致 10 mM 茶碱对未中毒纤维中钠外流的刺激作用减弱。向未中毒纤维中注射 Corbin 的蛋白抑制剂会导致 10 mM 茶碱的刺激作用减弱。在内部施加 Corbin 的抑制剂并外部施加 10 mM 茶碱后，向哇巴因中毒的纤维中注射 cAMP 未能使哇巴因不敏感的钠外流显著增加。在 10 mM 茶碱达到峰值刺激后，向哇巴因中毒的纤维中注射 Corbin 的抑制剂未能降低钠外流。注射 1 mM 和 100 mM EGTA 并暴露于 10 mM 茶碱的纤维，当茶碱浓度为 10 mM 时，对注射的 cAMP 的哇巴因不敏感钠外流反应明显降低。在含有 10 mM 茶碱的无 Ca2+ 人工海水中浸泡的纤维对注射的 cAMP 反应也很差。在向浴液中添加质子后，10 mM 茶碱未能增强对无 Ca2+ 的 3 mM - HEPES 人工海水或 10 mM - Ca2+ - 3 mM - HEPES 人工海水中哇巴因不敏感钠外流的刺激。在向浴液中添加茶碱后，注射 cAMP 也未观察到增强的反应。注射 8 - 氟茶碱、3 - 异丁基 - 1 - 甲基黄嘌呤和多桑唑会导致哇巴因不敏感钠外流对注射的 cAMP 的反应显著降低。注射这些物质时总会发生收缩。这些结果与茶碱主要通过降低肌浆 pCa（pCa = -log10[Ca2+]）起作用的理论一致，并且降低的 pCa 会由于新形成的 cGMP 激活 cGMP 依赖性蛋白激酶系统而导致对哇巴因不敏感的钠外流的刺激。