López-Colomé A M, Fragoso G, Wright C E, Sturman J A
Instituto de Fisiología Celular, UNAM, México, D. F.
Curr Eye Res. 1994 Aug;13(8):553-60. doi: 10.3109/02713689408999888.
The presence of specific, saturable receptor sites for excitatory amino acids (EAA) in membranes from cultured human retinal pigment epithelium (RPE) was established through the binding of [3H]L-glutamate (L-Glu). The age of the donors ranged from 6 days to 33 years. The affinity of the binding (KB) sites was between 1.2 and 1.5 microM, and did not change with the age of the donor, whereas the Bmax was slightly increased (8.6 to 13.0 pmol/mg) in membranes from the 33 year-old compared to the 29 day-old donor. The efficacy profile of agonists and antagonists acting at EAA receptors for displacing [3H]L-Glu was L-Glu = L-Aspartate > 2-amino-4-phosphonovalerate (AP5) > N-methyl-D-Aspartate (NMDA) > 1-aminocyclopentane-1,3 dicarboxylate (trans-ACPD) > 2-amino-3-phosphonopropionate (AP3). These data suggest the presence of either an NMDA-receptor sensitive to the metabotropic agonist trans-ACPD or alternatively, the presence of two different populations of receptors with similar affinity for the agonist: NMDA and metabotropic. Glycine highly stimulated Glu-binding; this effect was inversely related to the age of the donor. Taurine and to a lesser extent GABA, mimicked this effect. Stimulation by glycine was dose-dependent, insensitive to strychnine and 80% inhibited by 7-chlorokynurenate. This effect was also present in human RPE-derived fibroblasts, human scleral fibroblasts and the human lymphoblastoid cell line NB76, all continuously dividing cells. The results further support the possibility of the participation of EAA receptors in the regulation of phagocytosis in RPE.
通过[3H]L-谷氨酸（L-Glu）结合实验，证实了培养的人视网膜色素上皮（RPE）细胞膜中存在兴奋性氨基酸（EAA）的特异性、可饱和受体位点。供体年龄范围为6天至33岁。结合位点的亲和力（KB）在1.2至1.5微摩尔之间，且不随供体年龄变化，而与29日龄供体相比，33岁供体的细胞膜中最大结合量（Bmax）略有增加（从8.6皮摩尔/毫克增至13.0皮摩尔/毫克）。作用于EAA受体以置换[3H]L-Glu的激动剂和拮抗剂的效能谱为：L-Glu = L-天冬氨酸 > 2-氨基-4-磷酸戊酸（AP5）> N-甲基-D-天冬氨酸（NMDA）> 1-氨基环戊烷-1,3-二羧酸（反式-ACPD）> 2-氨基-3-磷酸丙酸（AP3）。这些数据表明存在对促代谢型激动剂反式-ACPD敏感的NMDA受体，或者存在对激动剂具有相似亲和力的两种不同受体群体：NMDA受体和促代谢型受体。甘氨酸能强烈刺激Glu结合；这种效应与供体年龄呈负相关。牛磺酸以及程度稍轻的γ-氨基丁酸（GABA）模拟了这种效应。甘氨酸的刺激呈剂量依赖性，对士的宁不敏感，且7-氯犬尿氨酸可抑制80%。这种效应在人RPE来源的成纤维细胞、人巩膜成纤维细胞和人淋巴母细胞系NB76（所有持续分裂的细胞）中也存在。结果进一步支持了EAA受体参与RPE吞噬作用调节的可能性。
