Fisher J L, Macdonald R L
Department of Neurology University of Michigan Medical Center, Ann Arbor 48104-1687, USA.
Neuropharmacology. 1997 Nov-Dec;36(11-12):1601-10. doi: 10.1016/s0028-3908(97)00133-0.
GABA(A) receptor (GABAR) isoforms in the central nervous system are composed of combinations of alpha(1-6), beta(1-4), gamma(1-4), delta(1) and epsilon(1) subunit subtypes arranged in a pentamer. Many regions of the brain express high levels of mRNA encoding several different subunits and even multiple subunit subtypes. The stoichiometry of GABAR isoforms is unclear, and the number and identity of individual subunit subtypes that are coassembled remain uncertain. To examine the role of beta subunit subtypes in the functional properties of GABARS and to determine whether multiple beta subtypes can be coassembled in functional GABARs, plasmids containing cDNAs encoding rat beta1 and/or beta3, alpha5 and gamma2L subtypes were cotransfected into L929 fibroblasts. The properties of the expressed receptor populations were determined using whole-cell and single-channel recording techniques. The alpha5beta1gamma2L isoform was less sensitive to GABA than the alpha5beta3gamma2L isoform. alpha5beta1gamma2L isoform currents were also insensitive to the allosteric modulator loreclezole, while alpha5beta3gamma2L isoform currents were strongly potentiated by loreclezole. Fibroblasts transfected with plasmids containing cDNAs for both beta1 and beta3 subtypes along with alpha5 and gamma2L subtypes produced a receptor population with an intermediate sensitivity to GABA which was insensitive to loreclezole. These results suggest that functional GABARs can be formed that contain two different beta1 subunit subtypes with properties different from receptors that contain only a single beta1 subtype and that the beta1 subunit subtypes influence the response of GABARs to GABA and to the allosteric modulator loreclezole.
中枢神经系统中的GABA(A)受体（GABAR）亚型由α(1 - 6)、β(1 - 4)、γ(1 - 4)、δ(1)和ε(1)亚基亚型组合而成，排列成五聚体。大脑的许多区域都高水平表达编码几种不同亚基甚至多种亚基亚型的mRNA。GABAR亚型的化学计量尚不清楚，共同组装的单个亚基亚型的数量和身份也不确定。为了研究β亚基亚型在GABAR功能特性中的作用，并确定多种β亚型是否可以共同组装到功能性GABAR中，将含有编码大鼠β1和/或β3、α5和γ2L亚型cDNA的质粒共转染到L929成纤维细胞中。使用全细胞和单通道记录技术确定表达的受体群体的特性。α5β1γ2L亚型对GABA的敏感性低于α5β3γ2L亚型。α5β1γ2L亚型电流对变构调节剂洛来唑也不敏感，而α5β3γ2L亚型电流则被洛来唑强烈增强。用同时含有β1和β3亚型以及α5和γ2L亚型cDNA的质粒转染的成纤维细胞产生了对GABA具有中等敏感性且对洛来唑不敏感的受体群体。这些结果表明，可以形成含有两种不同β1亚基亚型的功能性GABAR，其特性不同于仅含有单一β1亚型的受体，并且β1亚基亚型会影响GABAR对GABA和变构调节剂洛来唑的反应。
