Lee W J, Hawkins R A, Viña J R, Peterson D R
Department of Physiology and Biophysics, Finch University of Health Science, Chicago Medical School, Illinois 60064-3095, USA.
Am J Physiol. 1998 Apr;274(4):C1101-7. doi: 10.1152/ajpcell.1998.274.4.C1101.
Glutamine and glutamate transport activities were measured in isolated luminal and abluminal plasma membrane vesicles derived from bovine brain endothelial cells. Facilitative systems for glutamine and glutamate were almost exclusively located in luminal-enriched membranes. The facilitative glutamine carrier was neither sensitive to 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid inhibition nor did it participate in accelerated amino acid exchange; it therefore appeared to be distinct from the neutral amino acid transport system L1. Two Na-dependent glutamine transporters were found in abluminal-enriched membranes: systems A and N. System N accounted for approximately 80% of Na-dependent glutamine transport at 100 microM. Abluminal-enriched membranes showed Na-dependent glutamate transport activity. The presence of 1) Na-dependent carriers capable of pumping glutamine and glutamate from brain into endothelial cells, 2) glutaminase within endothelial cells to hydrolyze glutamine to glutamate and ammonia, and 3) facilitative carriers for glutamine and glutamate at the luminal membrane may provide a mechanism for removing nitrogen and nitrogen-rich amino acids from brain.
在源自牛脑内皮细胞的分离的管腔和管腔外质膜囊泡中测量了谷氨酰胺和谷氨酸的转运活性。谷氨酰胺和谷氨酸的易化转运系统几乎完全位于富含管腔的膜中。易化性谷氨酰胺载体既不敏感于2-氨基双环(2,2,1)庚烷-2-羧酸抑制，也不参与加速的氨基酸交换；因此，它似乎与中性氨基酸转运系统L1不同。在富含管腔外的膜中发现了两种钠依赖性谷氨酰胺转运体：系统A和系统N。在100微摩尔时，系统N约占钠依赖性谷氨酰胺转运的80%。富含管腔外的膜显示出钠依赖性谷氨酸转运活性。1）能够将谷氨酰胺和谷氨酸从脑泵入内皮细胞的钠依赖性载体、2）内皮细胞内将谷氨酰胺水解为谷氨酸和氨的谷氨酰胺酶、以及3）管腔膜上谷氨酰胺和谷氨酸的易化性载体的存在，可能为从脑中去除氮和富含氮的氨基酸提供一种机制。
