Eliasof S, Jahr C E
Vollum Institute, Oregon Health Sciences University, Portland 97201, USA.
Proc Natl Acad Sci U S A. 1996 Apr 30;93(9):4153-8. doi: 10.1073/pnas.93.9.4153.
Application of L-glutamate to retinal glial (Müller) cells results in an inwardly rectifying current due to the net influx of one positive charge per molecule of glutamate transported into the cell. However, at positive potentials an outward current can be elicited by glutamate. This outward current is eliminated by removal of external chloride ions. Substitution of external chloride with the anions thiocyanate, perchlorate, nitrate, and iodide, which are known to be more permeant at other chloride channels, results in a considerably larger glutamate-elicited outward current at positive potentials. The large outward current in external nitrate has the same ionic dependence, apparent affinity for L-glutamate, and pharmacology as the glutamate transporter previously reported to exist in these cells. Varying the concentration of external nitrate shifts the reversal potential in a manner consistent with a conductance permeable to nitrate. Together, these results suggest that the glutamate transporter in retinal glial cells is associated with an anionic conductance. This anionic conductance may be important for preventing a reduction in the rate of transport due the depolarization that would otherwise occur as a result of electrogenic glutamate uptake.
将L-谷氨酸应用于视网膜神经胶质（穆勒）细胞会产生内向整流电流，这是由于每分子谷氨酸转运进入细胞时净流入一个正电荷所致。然而，在正电位下，谷氨酸可引发外向电流。去除细胞外氯离子可消除这种外向电流。用硫氰酸盐、高氯酸盐、硝酸盐和碘化物等阴离子替代细胞外氯离子，已知这些阴离子在其他氯离子通道中更易通透，结果在正电位下谷氨酸引发的外向电流显著增大。外部硝酸盐中的大外向电流具有与先前报道存在于这些细胞中的谷氨酸转运体相同的离子依赖性、对L-谷氨酸的表观亲和力和药理学特性。改变外部硝酸盐的浓度会以与硝酸盐可通透的电导一致的方式改变反转电位。这些结果共同表明，视网膜神经胶质细胞中的谷氨酸转运体与阴离子电导相关。这种阴离子电导对于防止因电生性谷氨酸摄取导致的去极化而引起的转运速率降低可能很重要。
