Aguayo L G, Pancetti F C
Laboratory of Neuropharmacology, Catholic University at Valparaiso, Chile.
J Pharmacol Exp Ther. 1994 Jul;270(1):61-9.
The effects of ethanol on the GABA (gamma-aminobutyric acid)A-activated Cl- current were studied in cultured mouse hippocampal and cortical neurons using whole-cell techniques. Ethanol (0.25-200 mM) reversibly potentiated the current in 68 of the 131 hippocampal neurons examined. Ethanol also potentiated a strychnine-sensitive glycine-activated Cl- current in hippocampal and spinal neurons. Ethanol (40 mM) enhanced the maximal response to GABA without changing the Hill coefficient (1.2) or the affinity of the receptor for GABA (EC50 = 15 vs. 14 microM). We found neurons with distinct sensitivities to ethanol, and even concentrations of 425 and 850 mM further potentiated the response induced by GABA and glycine. Ethanol was able to potentiate the GABAA current even after removing Ca++ from the external solution. The protein kinase C activator phorbol, 12 myristate, 13 acetate inhibited the amplitude of the GABA current by 73 +/- 7% of control; however, 4-alpha-phorbol, 12 myristate, 13 acetate, its inactive analog, had no effects. In addition, 2 min of preapplication of 1 microM phorbol, 12 myristate, 13 acetate reduced the ethanol-potentiation from 140 +/- 8 to 122 +/- 6%. Recordings of GABA- and glycine-activated Cl- currents showed that low concentrations of ethanol can differentially affect these receptors in a single neuron. This suggests that the GABAergic effect of ethanol is not mediated by a nonspecific change and that different mechanisms might account for the potentiation of these two ligand-activated Cl- channels by ethanol. In addition, the absence of saturation with high concentrations suggests that ethanol modulates these receptor-ion channel complexes by acting in several sites, one of which might control the state of receptor phosphorylation.
采用全细胞技术，在培养的小鼠海马和皮层神经元中研究了乙醇对γ-氨基丁酸A（GABA）激活的氯离子电流的影响。在所检测的131个海马神经元中，68个神经元的乙醇（0.25 - 200 mM）可使电流可逆性增强。乙醇还可增强海马和脊髓神经元中对士的宁敏感的甘氨酸激活的氯离子电流。乙醇（40 mM）增强了对GABA的最大反应，而不改变希尔系数（1.2）或受体对GABA的亲和力（EC50 = 15对14 μM）。我们发现神经元对乙醇具有不同的敏感性，甚至425和850 mM的浓度进一步增强了GABA和甘氨酸诱导的反应。即使从外部溶液中去除钙离子后，乙醇仍能够增强GABAA电流。蛋白激酶C激活剂佛波醇12 -肉豆蔻酸酯13 -乙酸酯使GABA电流幅度抑制至对照的73±7%；然而，其无活性类似物4-α-佛波醇12 -肉豆蔻酸酯13 -乙酸酯则无作用。此外，预先应用1 μM佛波醇12 -肉豆蔻酸酯13 -乙酸酯2分钟可使乙醇增强作用从140±8%降至122±6%。GABA和甘氨酸激活的氯离子电流记录显示，低浓度乙醇可在单个神经元中对这些受体产生不同影响。这表明乙醇的GABA能效应不是由非特异性变化介导的，并且不同机制可能解释乙醇对这两种配体激活的氯离子通道的增强作用。此外，高浓度下无饱和现象表明乙醇通过作用于多个位点来调节这些受体-离子通道复合物，其中一个位点可能控制受体磷酸化状态。
