Efficacy of background GABA uptake in rat hippocampal slices.

GABA uptake is crucial for the termination of inhibitory synaptic events. In addition, GABA transporters may also control the level of diffusely distributed GABA in the extracellular space. We analysed this function by superfusing rat hippocampal slices with different concentrations of GABA. Whole-cell patch clamp recordings of CA1 pyramidal cells revealed small increases in chloride conductance at 5-10 microM GABA which increased dramatically upon addition of the GABA uptake blocker tiagabine. Tiagabine alone induced a significant chloride conductance indicating that spontaneous release of GABA in hippocampal slices is neutralized by GAT-1, the main hippocampal GABA transporter. Thus, GAT-1 clears the extracellular space in the hippocampus from diffusely distributed GABA with high efficacy.