Inhibition of Na +-dependent GABA uptake in isolated frog sensory nerve cell bodies by extra- and intracellular Li +

Abstract

The effect of Li + on the Na +-dependent γ-aminobutyric acid (GABA) uptake was investigated by examining the effects of external and internal Li + ([Li] o and [Li] i) on GABA-gated Cl − current ( I Cl) in the frog dorsal root ganglion cells using the suction pipette technique which allows the internal perfusion under voltage-clamp condition. The suppression of GABA responses in the presence of external Na + ([Na] o) was larger at lower than at higher GABA concentration. Replacement of [Na] o with Li + completely removed the Na + suppression, and GABA dose-response curve in Li + external solution agreed well with that in Na +-free (Tris +) external solution. Either increasing [Li] i or internal Na + ([Na] i) at a constant [Na] o equally reduced the Na +-dependent suppression of GABA-gated I Cl. The results indicate that both the [Li] o and [Li] i remove in different manner the [Na] o-dependent suppression of GABA-induced I Cl: i.e. the [Li] o acts as a blocker of Na +-GABA co-transport mechanism while the increase of [Li] i decreases the Na + electrochemical potential gradient across the soma membrane as well as [Na] i does.