Nonvesicular inhibitory neurotransmission via reversal of the GABA transporter GAT-1.
GABA transporters play an important but poorly understood role in neuronal inhibition. They can reverse, but this is widely thought to occur only under pathological conditions. Here we use a heterologous expression system to show that the reversal potential of GAT-1 under physiologically relevant conditions is near the normal resting potential of neurons and that reversal can occur rapidly enough to release GABA during simulated action potentials. We then use paired recordings from cultured hippocampal neurons and show that GABAergic transmission is not prevented by four methods widely used to block vesicular release. This nonvesicular neurotransmission was potently blocked by GAT-1 antagonists and was enhanced by agents that increase cytosolic [GABA] or [Na(+)] (which would increase GAT-1 reversal). We conclude that GAT-1 regulates tonic inhibition by clamping ambient [GABA] at a level high enough to activate high-affinity GABA(A) receptors and that transporter-mediated GABA release can contribute to phasic inhibition.
Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA.
Yuanming
Y
Wu
Wengang
W
Wang
Ana
A
Díez-Sampedro
George B
GB
Richerson
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D016466:CHO Cells; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004594:Electrophysiology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D050485:GABA Plasma Membrane Transport Proteins / Q000235:genetics / Q000502:physiology; D058805:GABA Uptake Inhibitors; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects / Q000502:physiology; D012964:Sodium / Q000378:metabolism / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013572:Synaptic Vesicles / Q000187:drug effects / Q000502:physiology*; D013816:Thermodynamics; D014162:Transfection; D005680:gamma-Aminobutyric Acid / Q000378:metabolism* / Q000502:physiology
D002712:Chlorides; D050485:GABA Plasma Membrane Transport Proteins; D058805:GABA Uptake Inhibitors; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D012964:Sodium