A bicarbonate-dependent increase in extracellular pH mediated by GABAA receptors in turtle cerebellum

The gamma-aminobutyric acid (GABA)-gated anion channel has been found to have a significant permeability to bicarbonate in isolated nerve cells and crayfish muscle. We have studied the extracellular pH of the in vitro turtle cerebellum to determine whether the extracellular pH of vertebrate brain can be modulated by GABA. Exposure to 10(-3) M GABA produced an extracellular alkaline transient with a mean amplitude of 0.054 +/- 0.19 pH units (n = 49, range 0.018-0.091 pH units). The GABA-evoked alkaline shift was blocked by picrotoxin and was dependent on the presence of HCO3- in the bathing media. These data suggest that GABAA receptors gate an HCO3(-)-efflux which is sufficient to modulate brain pH.