Influence of extracellular and intracellular pH on GABA-gated chloride conductance in crayfish muscle fibres.
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.
Pasternack
M
M
Department of Zoology, University of Helsinki, Finland.
Bountra
C
C
Voipio
J
J
Kaila
K
K
D000818:Animals; D003400:Astacoidea; D018118:Chloride Channels; D004305:Dose-Response Relationship, Drug; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000187:drug effects / Q000502:physiology*; D009118:Muscimol / Q000494:pharmacology; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D018118:Chloride Channels; D007473:Ion Channels; D008565:Membrane Proteins; D009118:Muscimol; D005680:gamma-Aminobutyric Acid