Yoon H, Fanelli A, Grollman E F, Philp N J
Pennsylvania College of Optometry, Philadelphia 19141-3399, USA.
Biochem Biophys Res Commun. 1997 May 8;234(1):90-4. doi: 10.1006/bbrc.1997.6588.
The retinal pigment epithelium transports lactate between two tissue compartments, the interphotoreceptor matrix and the choriocapillaris. In this report we describe a 2.45-kb cDNA isolated from a chick cDNA RPE library that encodes a membrane protein found only in RPE cells. The deduced protein has 542 amino acids with twelve putative membrane spanning domains. The cDNA has been designated MCT3 based on its 45% identity in amino acid sequence and structural similarity with the monocarboxylate transporters MCT1 and MCT2. Stable transfectants (pCl-neo/MCT3), made in a rat thyroid epithelial cell line (FRTL-5), express MCT3 RNA. Transfectants had enhanced pyruvate uptake (used as a measure of lactate uptake) which was proton-dependent and inhibited by alpha-cyano-4-hydroxycinnamate. In summary, MCT3's unique expression in RPE cells, multiple potential phosphorylation sites, and basolateral distribution suggest that MCT3 may regulate lactate levels in the interphotoreceptor space.
视网膜色素上皮细胞在两个组织间隙，即光感受器间基质和脉络膜毛细血管之间转运乳酸。在本报告中，我们描述了从鸡的cDNA视网膜色素上皮细胞文库中分离出的一个2.45 kb的cDNA，它编码一种仅在视网膜色素上皮细胞中发现的膜蛋白。推导的蛋白质有542个氨基酸，具有12个假定的跨膜结构域。基于其氨基酸序列45%的同一性以及与单羧酸转运蛋白MCT1和MCT2的结构相似性，该cDNA被命名为MCT3。在大鼠甲状腺上皮细胞系（FRTL-5）中构建的稳定转染子（pCl-neo/MCT3）表达MCT3 RNA。转染子的丙酮酸摄取（用作乳酸摄取的指标）增强，这是质子依赖性的，并被α-氰基-4-羟基肉桂酸抑制。总之，MCT3在视网膜色素上皮细胞中的独特表达、多个潜在的磷酸化位点以及基底外侧分布表明，MCT3可能调节光感受器间间隙中的乳酸水平。
