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| 2. |
- Birnir, Bryndis, et al.
(författare)
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A structural determinant of desensitization and allosteric regulation by pentobarbitone of the GABAA receptor.
- 1997
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Ingår i: Journal of Membrane Biology. - 0022-2631 .- 1432-1424. ; 155:2, s. 157-66
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Tidskriftsartikel (refereegranskat)abstract
- Functional properties of the alpha1beta1 GABAA receptor changes in a subunit-specific manner when a threonine residue in the M2 region at the 12' position was mutated to glutamine. The rate and extent of desensitization increased in all mutants but the rate of activation was faster in the beta1 mutants. A negligible plateau current and abolition of potentiation by pentobarbitone of the GABA-activated current depended on the Thr 12' Gln mutation being present in the beta1 subunit. The Hill coefficient of the peak current response to GABA was reduced to less than one also in a beta1 subunit-specific manner. It was concluded that the beta1 subunit dominated conformational changes activated by GABA.
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| 3. |
- Dalziel, J E, et al.
(författare)
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A threonine residue in the M2 region of the beta1 subunit is needed for expression of functional alpha1beta1 GABA(A) receptors.
- 1999
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Ingår i: European Journal of Pharmacology. - 0014-2999 .- 1879-0712. ; 370:3, s. 345-8
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Tidskriftsartikel (refereegranskat)abstract
- Although there is a high degree of homology in the M2 transmembrane segments of alpha1 and beta1 subunits, subunit-specific effects were observed in alpha1beta1 GABA(A) receptors expressed in Spodoptera frugipedra (Sf9) cells when the conserved 13' threonine residue in the M2 transmembrane region was mutated to alanine. When threonine 263 (13') was mutated to alanine in the beta1 subunit, high-affinity muscimol binding and the response to GABA were abolished. This did not occur when the threonine 263 (13') was mutated to alanine in the alpha1 subunit, but the rate of desensitisation increased and the effect of bicuculline, a competitive inhibitor, was reduced. The results show differential effects of subunits on receptor function and support a role for M2 in desensitisation.
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| 4. |
- Tierney, M L, et al.
(författare)
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Effects of mutating leucine to threonine in the M2 segment of alpha1 and beta1 subunits of GABAA alpha1beta1 receptors.
- 1996
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Ingår i: Journal of Membrane Biology. - 0022-2631 .- 1432-1424. ; 154:1, s. 11-21
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Tidskriftsartikel (refereegranskat)abstract
- The conserved leucine residues at the 9' positions in the M2 segments of alpha1 (L264) and beta1 (L259) subunits of the human GABAA receptor were replaced with threonine. Normal or mutant alpha1 subunits were co-expressed with normal or mutant beta1 subunits in Sf9 cells using the baculovirus/Sf9 expression system. Cells in which one or both subunits were mutated had a higher "resting" chloride conductance than cells expressing wild-type alpha1beta1 receptors. This chloride conductance was blocked by 10 mM penicillin, a recognized blocker of GABAA channels, but not by bicuculline (100 microm) or picrotoxin (100 microm) which normally inhibit the chloride current activated by GABA: nor was it potentiated by pentobarbitone (100 microM). In cells expressing wild-type beta1 with mutated alpha1 subunits, an additional chloride current could be elicited by GABA but the rise time and decay were slower than for wild-type alpha1beta1 receptors. In cells expressing mutated beta1 subunits with wild-type or mutated alpha1 subunits (alphabeta(L9'T) and alpha(L9'T)beta(L9'T)), no response to GABA could be elicited: this was not due to an absence of GABAA receptors in the plasmalemma because the cells bound [3H]-muscimol. It was concluded that in GABAA channels containing the L9'T mutation in the beta1 subunit, GABA-binding does not cause opening of channels, and that the L9'T mutation in either or both subunits gives an open-channel state of the GABAA receptor in the absence of ligand.
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