Two pools of Triton X-100-insoluble GABA(A) receptors are present in the brain, one associated to lipid rafts and another one to the post-synaptic GABAergic complex.
Rat forebrain synaptosomes were extracted with Triton X-100 at 4 degrees C and the insoluble material, which is enriched in post-synaptic densities (PSDs), was subjected to sedimentation on a continuous sucrose gradient. Two pools of Triton X-100-insoluble gamma-aminobutyric acid type-A receptors (GABA(A)Rs) were identified: (i) a higher-density pool (rho = 1.10-1.15 mg/mL) of GABA(A)Rs that contains the gamma2 subunit (plus alpha and beta subunits) and that is associated to gephyrin and the GABAergic post-synaptic complex and (ii) a lower-density pool (rho = 1.06-1.09 mg/mL) of GABA(A)Rs associated to detergent-resistant membranes (DRMs) that contain alpha and beta subunits but not the gamma2 subunit. Some of these GABA(A)Rs contain the delta subunit. Two pools of GABA(A)Rs insoluble in Triton X-100 at 4 degrees C were also identified in cultured hippocampal neurons: (i) a GABA(A)R pool that forms clusters that co-localize with gephyrin and remains Triton X-100-insoluble after cholesterol depletion and (ii) a GABA(A)R pool that is diffusely distributed at the neuronal surface that can be induced to form GABA(A)R clusters by capping with an anti-alpha1 GABA(A)R subunit antibody and that becomes solubilized in Triton X-100 at 4 degrees C after cholesterol depletion. Thus, there is a pool of GABA(A)Rs associated to lipid rafts that is non-synaptic and that has a subunit composition different from that of the synaptic GABA(A)Rs. Some of the lipid raft-associated GABA(A)Rs might be involved in tonic inhibition.
Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, USA.
Xuejing
X
Li
David R
DR
Serwanski
Celia P
CP
Miralles
Ben A
BA
Bahr
Angel L
AL
De Blas
D000818:Animals; D001921:Brain / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D002478:Cells, Cultured; D003902:Detergents / Q000494:pharmacology; D004622:Embryo, Mammalian; D005445:Flunitrazepam / Q000493:pharmacokinetics; D018757:GABA Modulators / Q000493:pharmacokinetics; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000378:metabolism; D046529:Microscopy, Electron, Transmission / Q000379:methods; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017830:Octoxynol / Q000494:pharmacology; D011869:Radioligand Assay / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000145:classification* / Q000378:metabolism*; D012503:Saponins / Q000494:pharmacology; D013347:Subcellular Fractions / Q000378:metabolism / Q000648:ultrastructure; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D003902:Detergents; D018757:GABA Modulators; D008565:Membrane Proteins; D011963:Receptors, GABA-A; D012503:Saponins; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam; D017830:Octoxynol