title: Identification of a unique monocarboxylate transporter (MCT3) in retinal pigment epithelium.
abstract: 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.
authors.affiliation: Pennsylvania College of Optometry, Philadelphia 19141-3399, USA.
authors.forename: H
authors.initials: H
authors.lastname: Yoon
authors.forename: A
authors.initials: A
authors.lastname: Fanelli
authors.forename: E F
authors.initials: EF
authors.lastname: Grollman
authors.forename: N J
authors.initials: NJ
authors.lastname: Philp
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D002645:Chickens; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D015870:Gene Expression / Q000235:genetics; D006031:Glycosylation; D019344:Lactic Acid / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D010857:Pigment Epithelium of Eye / Q000737:chemistry* / Q000378:metabolism; D011522:Protons; D019289:Pyruvic Acid / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017386:Sequence Homology, Amino Acid; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D018076:DNA, Complementary; C491393:Mct3 protein, rat; D026901:Membrane Transport Proteins; D011522:Protons; D012333:RNA, Messenger; D019344:Lactic Acid; D019289:Pyruvic Acid