Kreitzer Matthew A, Andersen Kristen A, Malchow Robert Paul
Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA.
J Physiol. 2003 Feb 1;546(Pt 3):717-31. doi: 10.1113/jphysiol.2002.034421.
Transport of the amino acid GABA into neurons and glia plays a key role in regulating the effects of GABA in the vertebrate retina. We have examined the modulation of GABA-elicited transport currents of retinal horizontal cells by glutamate, the likely neurotransmitter of vertebrate photoreceptors. Enzymatically isolated external horizontal cells of skate were examined using whole-cell voltage-clamp techniques. GABA (1 mM ) elicited an inward current that was completely suppressed by the GABA transport inhibitors tiagabine (10 microM) and SKF89976-A (100 microM), but was unaffected by 100 microM picrotoxin. Prior application of 100 microM glutamate significantly reduced the GABA-elicited current. Glutamate depressed the GABA dose-response curve without shifting the curve laterally or altering the voltage dependence of the current. The ionotropic glutamate receptor agonists kainate and AMPA also reduced the GABA-elicited current, and the effects of glutamate and kainate were abolished by the ionotropic glutamate receptor antagonist 6-cyano-7-nitroquinoxaline. NMDA neither elicited a current nor modified the GABA-induced current, and metabotropic glutamate analogues were also without effect. Inhibition of the GABA-elicited current by glutamate and kainate was reduced when extracellular calcium was removed and when recording pipettes contained high concentrations of the calcium chelator BAPTA. Caffeine (5 mM) and thapsigargin (2 nM), agents known to alter intracellular calcium levels, also reduced the GABA-elicited current, but increases in calcium induced by depolarization alone did not. Our data suggest that glutamate regulates GABA transport in retinal horizontal cells through a calcium-dependent process, and imply a close physical relationship between calcium-permeable glutamate receptors and GABA transporters in these cells.
氨基酸γ-氨基丁酸（GABA）向神经元和神经胶质细胞的转运在调节脊椎动物视网膜中GABA的作用方面起着关键作用。我们研究了谷氨酸（脊椎动物光感受器可能的神经递质）对视网膜水平细胞GABA引发的转运电流的调节作用。使用全细胞膜片钳技术对酶解分离的鳐鱼外侧水平细胞进行了检测。GABA（1 mM）引发内向电流，该电流被GABA转运抑制剂噻加宾（10 μM）和SKF89976 - A（100 μM）完全抑制，但不受100 μM苦味毒影响。预先施加100 μM谷氨酸可显著降低GABA引发的电流。谷氨酸使GABA剂量反应曲线压低，而不使其横向移动或改变电流的电压依赖性。离子型谷氨酸受体激动剂 kainate和AMPA也降低了GABA引发的电流，且谷氨酸和kainate的作用被离子型谷氨酸受体拮抗剂6 - 氰基 - 7 - 硝基喹喔啉消除。NMDA既不引发电流也不改变GABA诱导的电流，代谢型谷氨酸类似物也无作用。当去除细胞外钙且记录微电极含有高浓度钙螯合剂BAPTA时，谷氨酸和kainate对GABA引发电流的抑制作用减弱。咖啡因（5 mM）和毒胡萝卜素（2 nM）（已知可改变细胞内钙水平的试剂）也降低了GABA引发的电流，但仅由去极化诱导的钙增加则没有这种作用。我们的数据表明，谷氨酸通过钙依赖性过程调节视网膜水平细胞中的GABA转运，并暗示这些细胞中钙通透型谷氨酸受体与GABA转运体之间存在密切的物理关系。
