Identification of a unique monocarboxylate transporter (MCT3) in retinal pigment epithelium

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Biological Transport
  • Carrier Proteins / chemistry*
  • Carrier Proteins / genetics*
  • Carrier Proteins / metabolism
  • Cell Line
  • Chickens
  • Cloning, Molecular
  • DNA, Complementary / genetics
  • Gene Expression / genetics
  • Glycosylation
  • Lactic Acid / metabolism*
  • Membrane Transport Proteins
  • Microscopy, Fluorescence
  • Molecular Sequence Data
  • Pigment Epithelium of Eye / chemistry*
  • Pigment Epithelium of Eye / metabolism
  • Protons
  • Pyruvic Acid / metabolism
  • RNA, Messenger / metabolism
  • Rats
  • Sequence Homology, Amino Acid
  • Transfection


  • Carrier Proteins
  • DNA, Complementary
  • Mct3 protein, rat
  • Membrane Transport Proteins
  • Protons
  • RNA, Messenger
  • Lactic Acid
  • Pyruvic Acid

Associated data

  • GENBANK/U15685