Allosteric modulation of GABAA receptors by extracellular ATP.
BACKGROUND
The γ-aminobutyric acid type A receptor (GABAAR) is the primary receptor mediating fast synaptic inhibition in the brain and plays a critical role in modulation of neuronal excitability and neural networks. Previous studies have demonstrated that ATP and its nucleotide analogs may regulate the function of GABAARs via Ca2+-dependent intracellular mechanisms, which require activation of purinergic 2 (P2) receptors or cross-talk between two receptors.


RESULTS
Here, we report a potentiation of GABAARs by extracellular ATP via a previously un-recognized allosteric mechanism. Using cultured hippocampal neurons as well as HEK293 cells transiently expressing GABAARs, we demonstrate that extracellular ATP potentiates GABAAR mediated currents in a dose-dependent manner with an EC50 of 2.1 ± 0.2 mM. The potentiation was mediated by a postsynaptic mechanism that was not dependent on activation of either ecto-protein kinase or P2 receptors. Single channel recordings from cell-free excised membrane patches under outside-out mode or isolated membrane patches under cell-attached mode suggest that the ATP modulation of GABA currents is achieved through a direct action of ATP on the channels themselves and manifested by increasing the single channel open probability without alteration of its conductance. Moreover, this ATP potentiation of GABAAR could be reconstituted in HEK293 cells that transiently expressed recombinant rat GABAARs.


CONCLUSIONS
Our data strongly suggest that extracellular ATP allosterically potentiates GABAAR-gated chloride channels. This novel mode of ATP-mediated modulation of GABAARs may play an important role in regulating neuronal excitability and thereby in fine-tuning the excitation-inhibition balance under conditions where a high level of extracellular ATP is ensured.
Jun
J
Liu
Brain Research Centre and Department of Medicine, Vancouver Coastal Health Research Institute, University of British Columbia, Vancouver, BC V6T 2B5, Canada. ytwang@brain.ubc.ca.
Yu Tian
YT
Wang
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D002478:Cells, Cultured; D057809:HEK293 Cells; D006624:Hippocampus / Q000166:cytology; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013569:Synapses / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors
D011963:Receptors, GABA-A; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate