Inenaga K, Mason W T
Department of Neuroendocrinology, A.F.R.C. Institute of Animal Physiology, Babraham, Cambridge, U.K.
Neuroscience. 1987 Nov;23(2):649-60. doi: 10.1016/0306-4522(87)90083-2.
The effects of GABA, the analogues muscimol and baclofen, and the antagonist bicuculline were investigated on cultured primary bovine lactotrophs using the patch clamp technique. Under voltage clamp in the whole cell mode using solutions containing chloride as the only permeable ion, GABA application increased the amplitude of mean membrane current and fluctuations of current about this mean. Statistical analysis of current fluctuations induced by GABA showed that the power density spectra in 8 of 12 cells were best fitted to double Lorentzian functions and the variance was smallest around the estimated equilibrium potential of chloride ions. The underlying channel open time estimated from noise analysis was only weakly voltage-dependent. The variance of current noise increased with GABA concentration within the range of 1-30 microM, although a slight decrease of variance in one cell could be observed at 30 microM, suggesting that desensitization to GABA might occur. Muscimol mimicked the effect of GABA but baclofen was without effect under these conditions. Bicuculline reduced the GABA-activated membrane current fluctuations. GABA- or muscimol-activated channels recorded in isolated outside-out patches had a slope conductance of about 20 pS. Mean open times of the channel were characterized by two exponential decay functions. We conclude that bovine lactotrophs have GABA-activated chloride channels, which appear to be voltage-independent. In addition, the action of GABA appears to be mediated through the GABAA receptor subtype.
采用膜片钳技术，研究了γ-氨基丁酸（GABA）、其类似物蝇蕈醇和巴氯芬以及拮抗剂荷包牡丹碱对原代培养牛催乳细胞的作用。在全细胞模式下进行电压钳制，使用仅含氯离子作为唯一可通透离子的溶液，施加GABA可增加平均膜电流幅度以及围绕该平均值的电流波动。对GABA诱导的电流波动进行统计分析表明，12个细胞中有8个细胞的功率密度谱最适合双洛伦兹函数，并且在估计的氯离子平衡电位附近方差最小。根据噪声分析估计的基础通道开放时间仅微弱地依赖电压。在1 - 30微摩尔范围内，电流噪声的方差随GABA浓度增加，尽管在30微摩尔时可观察到一个细胞中的方差略有下降，提示可能发生了对GABA的脱敏作用。在这些条件下，蝇蕈醇模拟了GABA的作用，但巴氯芬无作用。荷包牡丹碱降低了GABA激活的膜电流波动。在分离的外向型膜片中记录的GABA或蝇蕈醇激活的通道的斜率电导约为20皮安。通道的平均开放时间由两个指数衰减函数表征。我们得出结论，牛催乳细胞具有GABA激活的氯离子通道，这些通道似乎不依赖电压。此外，GABA的作用似乎是通过GABAA受体亚型介导的。
