Functional GABAA receptor heterogeneity of acutely dissociated hippocampal CA1 pyramidal cells.
Functional GABAA receptor heterogeneity of acutely dissociated hippocampal CA1 pyramidal cells.
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急性分离海马 CA1 锥体细胞的功能 GABAA 受体异质性。
DOI：
10.1152/jn.1999.81.4.1575
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发表时间：
1999
影响因子：
2.5
通讯作者：
Macdonald,RL
中科院分区：
文献类型：
--
作者：
Tietz,EI;Kapur,J;Macdonald,RL
急性分离海马CA 1区锥体细胞的GABA A受体功能异质性 CA 1锥体细胞电压钳位，GABA施加到单个细胞与一个修改的U型管，快速药物应用系统。当Vh = −50 mV时，10 μM GABA诱发的内向电流可被GABA A受体（GABAR）拮抗剂抑制，且对巴氯芬不敏感，表明GABA对分离的CA 1锥体细胞的作用是GABAR介导的。所有细胞的平均GABA浓度-反应曲线与双位点方程拟合最佳，表明在两个或多个细胞群上至少存在两个GABA结合位点，一个高亲和力位点（EC 50 -1= 11.0 μM）和一个低亲和力位点（EC 50 -2= 334.2 μM）。GABAR变构调节剂对浓度依赖性GABAR电流峰值的影响是复杂的，包括单相（loreclezole）或多相（地西泮）增强，混合增强/抑制（DMCM，唑吡坦）或多相抑制（锌）。地西泮对GABAR电流的单相（70%的细胞）或双相（30%的细胞）增强表明GABAR上有三个不同的位点（EC 50 -1=1.8 nM; EC 50 -2= 75.8 nM; EC 50 -3= 275.9 nM），揭示了GABAR的异质性。咪唑并吡啶唑吡坦在70%的细胞中增强GABAR电流，EC 50 = 222.5 nM，表明中等亲和力的含α2（或α3-）亚型的BZ IIA型受体占优势。一小部分细胞（10%）对唑吡坦具有高亲和力，这提示含有α1亚型的BZ I型受体。其余30%的细胞对唑吡坦不敏感或受唑吡坦抑制，表明存在含α5亚型的BZ IIB型受体。无法确定BZ I型和II型受体是否共存。β-咔啉甲基6，7-二甲氧基-4-乙基-β-咔啉-3-羧酸酯（DMCM）在中纳摩尔浓度下抑制所有细胞中的GABAR电流，但此外，在低纳摩尔浓度下增强某些细胞中的GABAR电流，表征了两组细胞，后者可能是由于α5βxγ 2GABAR的功能组装。在所有细胞中，GABAR电流对洛瑞唑中度敏感（EC 50 = 9 μM），与β3亚型亚基mRNA表达相对大于β1亚型亚基mRNA表达一致。根据对锌的敏感性（IC 50 = 28和182 μM）鉴定了两个细胞群，表明存在至少两种GABAR亚型，包括α5β3γ2 GABAR。与海马中GABAR亚基mRNA和蛋白质表达的异质性一致，并且基于它们对GABA和变构调节剂的不同反应，不同的CA 1锥体细胞群体可能表达多种功能性GABAR同种型。
Functional GABAAreceptor heterogeneity of acutely dissociated hippocampal CA1 pyramidal cells. CA1 pyramidal cells were voltage clamped, and GABA was applied to individual cells with a modified U-tube, rapid drug application system. WithVh= −50 mV, inward currents elicited by 10 μM GABA were inhibited by GABAAreceptor (GABAR) antagonists and were baclofen insensitive, suggesting that GABA actions on isolated CA1 pyramidal cells were GABAR mediated. GABA concentration-response curves averaged from all cells were fitted best with a two-site equation, indicating the presence of at least two GABA binding sites, a higher-affinity site (EC50–1= 11.0 μM) and a lower-affinity site (EC50–2= 334.2 μM), on two or more populations of cells. The effects of GABAR allosteric modulators on peak concentration-dependent GABAR currents were complex and included monophasic (loreclezole) or multiphasic (diazepam) enhancement, mixed enhancement/inhibition (DMCM, zolpidem) or multiphasic inhibition (zinc). Monophasic (70% of cells) or biphasic (30% of cells) enhancement of GABAR currents by diazepam suggested three different sites on GABARs (EC50–1=1.8 nM; EC50–2= 75.8 nM; EC50–3= 275.9 nM) revealing GABAR heterogeneity. The imidazopyridine zolpidem enhanced GABAR currents in 70% of cells with an EC50= 222.5 nM, suggesting a predominance of moderate affinity α2 (or α3-) subtype-containing BZ Type IIA receptors. A small fraction of cells (10%) had a high affinity for zolpidem, something that is suggestive of α1 subtype-containing BZ Type I receptors. The remaining 30% of cells were insensitive to or inhibited by zolpidem, suggesting the presence of α5 subtype-containing BZ Type IIB receptors. Whether BZ Type I and Type II receptors coexist could not be determined. The β-carboline methyl 6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM) inhibited GABAR currents in all cells at midnanomolar concentrations, but in addition, potentiated GABAR currents in some cells at low nanomolar concentrations, characterizing two groups of cells, the latter likely due to functional assembly of α5βxγ2GABARs. In all cells, GABAR currents were moderately sensitive (EC50= 9 μM) to loreclezole, consistent with a relatively greater β3 subtype, than β1 subtype, subunit mRNA expression. Two populations of cells were identified based on their sensitivities to zinc(IC50= 28 and 182 μM), suggesting the presence of at least two GABAR isoforms including α5β3γ2 GABARs. Consistent with the heterogeneity of expression of GABAR subunit mRNA and protein in the hippocampus and based on their differential responses to GABA and to allosteric modulators, distinct populations of CA1 pyramidal cells likely express multiple, functional GABAR isoforms.