Henmi S, Imaizumi Y, Muraki K, Watanabe M
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University, Japan.
Eur J Pharmacol. 1995 Aug 25;282(1-3):219-28. doi: 10.1016/0014-2999(95)00339-m.
Characteristics of caffeine-induced inward current (Icaf) and spontaneous transient inward current were examined in single smooth muscle cells isolated from guinea-pig trachea. When a pipette solution contained mainly CsCl, an application of 10 mM caffeine elicited transient Icaf at a holding potential of -60 mV. Spontaneous transient inward currents were recorded in about 15% of cells examined and were abolished by caffeine. Both were Cl- current activated by an increase in intracellular Ca2+ concentration (ICl-Ca). When 10 mM caffeine was puff-applied twice with various intervals, the amplitude of the second Icaf depended upon the period of the interval. The relationship between the amplitude and the interval represents the recovery time course of Icaf, which was significantly slowed by 30 microM cyclopiazonic acid. The Icaf was not significantly affected by addition of Cd2+. Removal of external Ca2+ did not affect the first Icaf but markedly reduced the second one, regardless of the presence of Cd2+. In conclusion, Icaf is evoked by activation of ICl-Ca via Ca2+ release. The recovery time course of Icaf indicates the refilling of Ca2+ storage sites by the cyclopiazonic acid-sensitive Ca2+ pump. The refilling at -60 mV depends strongly upon Ca2+ influx through the Cd(2+)-insensitive pathway. Spontaneous transient inward currents may be also due to ICl-Ca activated by spontaneous Ca2+ release from local storage sites.
在从豚鼠气管分离出的单个平滑肌细胞中，研究了咖啡因诱导的内向电流（Icaf）和自发性瞬时内向电流的特性。当移液管溶液主要含有氯化铯时，施加10 mM咖啡因会在-60 mV的钳制电位下引发瞬时Icaf。在约15%的被检测细胞中记录到自发性瞬时内向电流，且该电流可被咖啡因消除。两者均为由细胞内Ca2+浓度升高激活的Cl-电流（ICl-Ca）。当以不同间隔两次微量施加10 mM咖啡因时，第二个Icaf的幅度取决于间隔时间。幅度与间隔时间之间的关系代表了Icaf的恢复时间进程，该进程被30 microM环匹阿尼酸显著减慢。添加Cd2+对Icaf无显著影响。去除细胞外Ca2+对第一个Icaf无影响，但无论是否存在Cd2+，均会显著降低第二个Icaf。总之，Icaf是通过Ca2+释放激活ICl-Ca而诱发的。Icaf的恢复时间进程表明环匹阿尼酸敏感的Ca2+泵对Ca2+储存位点的再填充。在-60 mV时的再填充强烈依赖于通过Cd(2+)不敏感途径的Ca2+内流。自发性瞬时内向电流也可能归因于从局部储存位点自发性释放Ca2+所激活的ICl-Ca。
