GABA(A) receptors containing the alpha4-subunit: prevalence, distribution, pharmacology, and subunit architecture in situ.
Recombinant GABA(A) receptors, expressed from alpha-, beta-, and gamma2-subunits, are diazepam-insensitive when the alpha-subunit is either alpha4 or alpha6. In situ, diazepam-insensitive receptors containing the alpha6-subunit are almost exclusively expressed in the granule cell layer of the cerebellum. However, diazepam-insensitive receptors are also expressed in forebrain areas. Here, we report on the presence of diazepam-insensitive GABA(A) receptors in various brain areas containing the alpha4-subunit. GABA(A) receptors immunoprecipitated with a newly developed alpha4-subunit-specific antiserum displayed a drug binding profile that was indistinguishable from those of alpha4beta2gamma2-recombinant receptors and diazepam-insensitive [3H]Ro 15-4513 binding sites in rat brain membranes. In addition, alpha4-subunit containing receptors and forebrain diazepam-insensitive receptors are present at comparably low abundance in rat brain and exhibit virtually identical patterns of distribution. Analysis of the subunit architecture of alpha4-subunit containing receptors revealed that the alpha4-subunit contributes to several receptor subtypes. Depending on the brain region, the alpha4-subunit can be coassembled with a second type of alpha-subunit variant being alpha1, alpha2, or alpha3. The data demonstrate that native receptors containing the alpha4-subunit are structurally heterogeneous, expressed at very low abundance in the brain, and display the drug binding profile of diazepam-insensitive [3H]Ro 15-4513 binding sites. Pharmacologically, these receptors may contribute to the actions of nonclassical ligands such as Ro 15-4513 and bretazenil.
Benke
D
D
Institute of Pharmacology, ETH and University of Zurich, Switzerland.
Michel
C
C
Mohler
H
H
D000818:Animals; D001386:Azides / Q000378:metabolism; D001569:Benzodiazepines / Q000378:metabolism; D001570:Benzodiazepinones / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002531:Cerebellum / Q000737:chemistry; D003975:Diazepam / Q000494:pharmacology; D005442:Flumazenil / Q000378:metabolism; D007150:Immunohistochemistry; D007163:Immunosorbent Techniques; D046911:Macromolecular Substances; D008297:Male; D009118:Muscimol / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000032:analysis* / Q000737:chemistry* / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism
D001386:Azides; D001570:Benzodiazepinones; D046911:Macromolecular Substances; D011963:Receptors, GABA-A; D011994:Recombinant Proteins; D001569:Benzodiazepines; D009118:Muscimol; D005442:Flumazenil; C042957:Ro 15-4513; C054626:bretazenil; D003975:Diazepam