Pasternack M, Bountra C, Voipio J, Kaila K
Department of Zoology, University of Helsinki, Finland.
Neuroscience. 1992;47(4):921-9. doi: 10.1016/0306-4522(92)90040-9.
The effect of intracellular and extracellular pH on GABA-gated Cl- conductance was studied using H(+)-selective microelectrodes and a three-microelectrode voltage clamp in crayfish leg opener muscle fibres in bicarbonate-free solutions. Experimental variation of intracellular pH in the range 6.4-8.0 did not affect the GABA-gated conductance. In contrast to this, the GABA-gated conductance was sensitive to changes in external pH. Raising the external pH from 7.4 to 8.4 decreased the GABA-gated peak conductance observed immediately following application of GABA by 30%, and a change from 7.4 to 6.4 produced an increase of 26%. The effect of extracellular pH on the GABA-gated peak conductance was approximately linear in the pH range 6.4-8.9. A slight decrease in the slope of the pH-conductance relationship was evident in the pH range 5.4-6.4. The desensitization of the GABA-gated conductance was also affected by external pH. At pH 6.9 the conductance produced by 1 mM GABA showed a desensitization of about 15%, and at pH 8.9 this value was 34%. Raising the external pH in the presence of GABA decreased the GABA-gated peak conductance and increased the fractional desensitization, while lowering the external pH produced opposite effects, and was capable of repriming the conductance from a desensitized state to the non-desensitized state. The above results show that the GABA-gated conductance is sensitive to changes in external pH in the physiological range, and suggest that pH-dependent changes in the postsynaptic efficacy of GABA-mediated inhibition may contribute to H+ modulation of neuronal excitability.
在无碳酸氢盐溶液中，使用氢离子选择性微电极和三微电极电压钳，研究了细胞内和细胞外pH值对GABA门控氯离子电导的影响。在小龙虾腿部伸肌纤维中，细胞内pH值在6.4 - 8.0范围内的实验性变化不影响GABA门控电导。与此相反，GABA门控电导对外部pH值的变化敏感。将外部pH值从7.4提高到8.4，使施加GABA后立即观察到的GABA门控峰值电导降低了30%，而从7.4变为6.4则使峰值电导增加了26%。在6.4 - 8.9的pH范围内，细胞外pH值对GABA门控峰值电导的影响大致呈线性。在5.4 - 6.4的pH范围内，pH - 电导关系的斜率略有下降。GABA门控电导的脱敏也受外部pH值的影响。在pH 6.9时，1 mM GABA产生的电导表现出约15%的脱敏，而在pH 8.9时，该值为34%。在存在GABA的情况下提高外部pH值会降低GABA门控峰值电导并增加脱敏分数，而降低外部pH值则产生相反效果，并且能够使电导从脱敏状态恢复到非脱敏状态。上述结果表明，GABA门控电导在生理范围内对外部pH值变化敏感，并提示GABA介导的抑制的突触后效能中依赖pH的变化可能有助于H⁺对神经元兴奋性的调节。
