White G, Li C, Ishac E
Section of Electrophysiology, National Institute on Alcohol Abuse and Alcoholism, Rockville, MD 20852.
Brain Res. 1992 Jul 17;586(1):157-61. doi: 10.1016/0006-8993(92)91388-u.
The effect of forskolin on GABAA receptor activated events has been the subject of recent investigations, the conclusions of which are conflicting. Forskolin can reduce current amplitude and increase the rate of decay of current activated by 100 microM GABA and these effects are not mimicked by 1,9-dideoxyforskolin (Tehrani et al., Synapse, 4 (1989) 126-131). On the other hand, both forskolin and 1,9-dideoxyforskolin inhibit 36Cl- flux induced by lower concentrations of muscimol (Heuschneider and Schwartz, Proc. Natl. Acad. Sci. USA, 86 (1989) 2938-2942). Using the whole-cell patch clamp technique to measure GABA activated current in dorsal root ganglion neurons that were freshly isolated from adult rats, we have confirmed the finding of Tehrani et al. (Synapse, 4 (1989) 126-131) using 100 microM GABA; however, the effects of forskolin that were not mimicked by 1,9-dideoxyforskolin were not blocked by the kinase inhibitor H-7 (50 microM). In contrast, at lower concentrations of GABA (10-20 microM), both forskolin and 1,9-dideoxyforskolin increased the decay rate of GABA activated current. In addition, all effects of forskolin occurred within 200 ms of application of forskolin and the effects were not blocked or occluded by H-7, 10 microM cAMP, or the active subunit of protein kinase A. We conclude that: (1) 1,9-dideoxyforskolin is not a reliable indicator of forskolin specificity in this system because its effects are dependent upon GABA concentration; and (2) the most prominent effects of forskolin on amplitude and decay time course of GABA activated ion current are not mediated by cAMP or protein kinase A (PKA).
毛喉素对γ-氨基丁酸A型（GABAA）受体激活事件的影响是近期研究的主题，但其结论相互矛盾。毛喉素可降低电流幅度，并增加由100微摩尔γ-氨基丁酸激活的电流的衰减速率，而1,9-二脱氧毛喉素无法模拟这些效应（Tehrani等人，《突触》，4（1989年）126 - 131页）。另一方面，毛喉素和1,9-二脱氧毛喉素均可抑制较低浓度蝇蕈醇诱导的36Cl-通量（Heuschneider和Schwartz，《美国国家科学院院刊》，86（1989年）2938 - 2942页）。我们采用全细胞膜片钳技术测量从成年大鼠新鲜分离的背根神经节神经元中γ-氨基丁酸激活的电流，已证实Tehrani等人（《突触》，4（1989年）126 - 131页）使用100微摩尔γ-氨基丁酸时的发现；然而，1,9-二脱氧毛喉素无法模拟的毛喉素效应并未被激酶抑制剂H - 7（50微摩尔）阻断。相反，在较低浓度的γ-氨基丁酸（10 - 20微摩尔）下，毛喉素和1,9-二脱氧毛喉素均增加了γ-氨基丁酸激活电流的衰减速率。此外，毛喉素的所有效应均在施加毛喉素后200毫秒内出现，且这些效应未被H - 7、10微摩尔环磷酸腺苷（cAMP）或蛋白激酶A的活性亚基阻断或掩盖。我们得出以下结论：（1）在该系统中，1,9-二脱氧毛喉素不是毛喉素特异性的可靠指标，因为其效应取决于γ-氨基丁酸浓度；（2）毛喉素对γ-氨基丁酸激活离子电流的幅度和衰减时间进程的最显著影响并非由cAMP或蛋白激酶A（PKA）介导。
