Bormann J, Rundström N, Betz H, Langosch D
Max-Planck-Institut für Hirnforschung, Frankfurt, Germany.
EMBO J. 1993 Oct;12(10):3729-37. doi: 10.1002/j.1460-2075.1993.tb06050.x.
We have expressed glycine receptor (GlyR) alpha and beta subunit cDNAs in HEK-293 cells to study the functional properties of homo- versus hetero-oligomeric GlyR channels. Dose-response curves of whole-cell currents in cells expressing alpha 1 subunits revealed an average Hill coefficient of h = 4.2. Co-expression with the beta subunit markedly increased glycine-gated whole-cell currents, which now exhibited a mean Hill coefficient of only h = 2.5. For alpha 1, alpha 2 and alpha 3 homo-oligomers, the main-state single-channel conductances were 86, 111 and 105 pS, respectively, recorded at symmetrical Cl- concentrations of 145 mM. The mutant alpha 1 G221A gave rise to a main-state of 107 pS. This indicates that the main-state of alpha homo-oligomers depends on residue 221 which is located within transmembrane segment M2. Importantly, the main-state conductances of alpha 1/beta, alpha 2/beta and alpha 3/beta hetero-oligomers were only 44, 54 and 48 pS, respectively. The latter values are similar to those found in spinal neurons, suggesting that native GlyRs are predominantly alpha/beta hetero-oligomers. Co-expression of alpha 1 with mutant beta subunits revealed that residues within and close to segment M2 of the beta subunit determine the conductance differences between homo- and hetero-oligomers.
我们在HEK-293细胞中表达了甘氨酸受体（GlyR）的α和β亚基cDNA，以研究同型和异型寡聚GlyR通道的功能特性。表达α1亚基的细胞中全细胞电流的剂量反应曲线显示平均希尔系数h = 4.2。与β亚基共表达显著增加了甘氨酸门控的全细胞电流，此时平均希尔系数仅为h = 2.5。对于α1、α2和α3同型寡聚体，在145 mM对称Cl-浓度下记录的主要状态单通道电导分别为86、111和105 pS。突变体α1 G221A产生的主要状态为107 pS。这表明α同型寡聚体的主要状态取决于位于跨膜片段M2内的第221位残基。重要的是，α1/β、α2/β和α3/β异型寡聚体的主要状态电导分别仅为44、54和48 pS。后一组值与在脊髓神经元中发现的值相似，这表明天然GlyRs主要是α/β异型寡聚体。α1与突变β亚基的共表达表明，β亚基M2片段内及附近的残基决定了同型和异型寡聚体之间的电导差异。
