Robinson M B, Hunter-Ensor M, Sinor J
Department of Pediatrics and Pharmacology, University of Pennsylvania, Children's Hospital of Philadelphia 19104.
Brain Res. 1991 Mar 29;544(2):196-202. doi: 10.1016/0006-8993(91)90054-y.
The transport of L-[3H]glutamate into crude synaptosomal membrane fractions prepared from cerebellum, brainstem, hippocampus, cortex, striatum, and midbrain was characterized. In all brain regions, greater than 95% of the accumulation of radiolabel was sodium-dependent and the concentration-dependence was consistent with a single high affinity site. Dihydrokainate and L-alpha-aminoadipate were region specific inhibitors of uptake; this inhibition was consistent with a competitive mechanism. In the forebrain regions examined, dihydrokainate inhibited transport with IC50s of approx. 100 microM (range from 80 to 170 microM). Transport in cerebellum was essentially dihydrokainate-insensitive L-alpha-Aminoadipate inhibited transport in forebrain regions with IC50s of approx. 700 microM (range from 590 to 800 microM) and inhibited transport in cerebellum with an IC50 of 40 microM. The inhibition data obtained with forebrain and cerebellar tissues were consistent with nearly homogeneous (greater than 80%) populations of non-interacting sites. Inhibition data obtained with tissue prepared from brainstem were best fit to a mixture of the two sites (35-50% of the type observed in cerebellum). Other previously identified uptake inhibitors, including DL-threo-hydroxyaspartate, L-aspartate-beta-hydroxamate, beta-glutamate, and L-cysteine sulfinate were not selective for the two types of transport. These data demonstrate that there are two pharmacologically distinct sodium-dependent high affinity transport systems with heterogeneous regional distributions.
对从小脑、脑干、海马体、皮层、纹状体和中脑制备的粗制突触体膜组分中L-[3H]谷氨酸的转运进行了表征。在所有脑区中，超过95%的放射性标记积累是钠依赖性的，且浓度依赖性与单一高亲和力位点一致。二氢海因酸和L-α-氨基己二酸是摄取的区域特异性抑制剂；这种抑制与竞争机制一致。在所研究的前脑区域中，二氢海因酸以约100μM（范围为80至170μM）的IC50抑制转运。小脑的转运对二氢海因酸基本不敏感。L-α-氨基己二酸以前脑区域约700μM（范围为590至800μM）的IC50抑制转运，并以40μM的IC50抑制小脑的转运。从前脑组织和小脑组织获得的抑制数据与几乎均一（大于80%）的非相互作用位点群体一致。从脑干制备的组织获得的抑制数据最符合两种位点的混合物（在小脑中观察到的类型的35 - 50%）。其他先前确定的摄取抑制剂，包括DL-苏式-羟基天冬氨酸、L-天冬氨酸-β-羟肟酸、β-谷氨酸和L-半胱氨酸亚磺酸盐对这两种转运类型没有选择性。这些数据表明存在两种药理学上不同的钠依赖性高亲和力转运系统，具有异质性区域分布。
