Effect of gamma-aminobutyric acid on intracellular pH in the crayfish stretch-receptor neurone.
The effect of gamma-aminobutyric acid (GABA) on intracellular pH (pHi) was examined in the crayfish stretch-receptor neurone using H(+)-selective microelectrodes and a two-microelectrode voltage clamp. In the presence of 30 mmol l-1 HCO3- (pH 7.4), application of GABA (0.5 mmol l-1) produced a mean fall in pHi of 0.26 units. The initial rate of fall of pHi was attributable to a net influx of acid equivalents of 6.3 mmol l-1 min-1. In the nominal absence of HCO3-, GABA had little effect on pHi. The HCO3(-)-dependent acidosis caused by GABA was inhibited by picrotoxin (0.1 mmol l-1) but not by depletion of extracellular and intracellular Cl-. Acetazolamide (0.1 mmol l-1) decreased the rate of fall of pHi caused by a step increase in CO2 partial pressure as well as by GABA, which indicates that the neurone contains carbonic anhydrase. In the presence of both Cl- and HCO3-, the reversal potential of the GABA-activated current was more positive than under nominally HCO3(-)-free conditions. In line with this, GABA induced a marked HCO3(-)-dependent depolarization, and this depolarizing action was enhanced in the absence of Cl- so as to lead to triggering of action potentials. All these observations support the conclusion that the GABA-induced fall in pHi is due to a net efflux of HCO3- through the inhibitory anion channels.
Voipio
J
J
Department of Zoology, University of Helsinki, Finland.
Pasternack
M
M
Rydqvist
B
B
Kaila
K
K
D000086:Acetazolamide; D000200:Action Potentials; D000818:Animals; D003400:Astacoidea; D001639:Bicarbonates / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000378:metabolism; D008465:Mechanoreceptors / Q000378:metabolism / Q000502:physiology*; D008564:Membrane Potentials; D008839:Microelectrodes; D010852:Picrotoxin; D013570:Synaptic Membranes / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D000086:Acetazolamide; D001639:Bicarbonates; D002712:Chlorides; D007473:Ion Channels; D010852:Picrotoxin; D005680:gamma-Aminobutyric Acid