| First Author | Benkherouf AY | Year | 2019 |
| Journal | J Neurochem | Volume | 149 |
| Issue | 1 | Pages | 41-53 |
| PubMed ID | 30565258 | Mgi Jnum | J:273199 |
| Mgi Id | MGI:6286566 | Doi | 10.1111/jnc.14646 |
| Citation | Benkherouf AY, et al. (2019) Extrasynaptic delta-GABAA receptors are high-affinity muscimol receptors. J Neurochem 149(1):41-53 |
| abstractText | Muscimol, the major psychoactive ingredient in the mushroom Amanita muscaria, has been regarded as a universal non-selective GABA-site agonist. Deletion of the GABAA receptor (GABAA R) delta subunit in mice (deltaKO) leads to a drastic reduction in high-affinity muscimol binding in brain sections and to a lower behavioral sensitivity to muscimol than their wild type counterparts. Here, we use forebrain and cerebellar brain homogenates from WT and deltaKO mice to show that deletion of the delta subunit leads to a > 50% loss of high-affinity 5 nM [(3) H]muscimol-binding sites despite the relatively low abundance of delta-containing GABAA Rs (delta-GABAA R) in the brain. By subtracting residual high-affinity binding in deltaKO mice and measuring the slow association and dissociation rates we show that native delta-GABAA Rs in WT mice exhibit high-affinity [(3) H]muscimol-binding sites (KD ~1.6 nM on alpha4betadelta receptors in the forebrain and ~1 nM on alpha6betadelta receptors in the cerebellum at 22 degrees C). Co-expression of the delta subunit with alpha6 and beta2 or beta3 in recombinant (HEK 293) expression leads to the appearance of a slowly dissociating [(3) H]muscimol component. In addition, we compared muscimol currents in recombinant alpha4beta3delta and alpha4beta3 receptors and show that delta subunit co-expression leads to highly muscimol-sensitive currents with an estimated EC50 of around 1-2 nM and slow deactivation kinetics. These data indicate that delta subunit incorporation leads to a dramatic increase in GABAA R muscimol sensitivity. We conclude that biochemical and behavioral low-dose muscimol selectivity for delta-subunit-containing receptors is a result of low nanomolar-binding affinity on delta-GABAA Rs. |
