1 Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia 19107; and 2 Department of Basic Sciences, Pennsylvania College of Optometry, Elkins Park, Pennsylvania 19027
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Monocarboxylate transporters (MCTs) are a family of highly homologous membrane proteins that mediate the 1:1 transport of a proton and a lactate ion. In chicken, MCT3 is preferentially expressed in the retinal pigment epithelium (RPE). We have isolated the mouse MCT3 cDNA and gene and characterized the pattern of tissue expression. MCT3 is a single copy gene with a 1.8-kb transcript that encodes a protein with a predicted molecular mass of 51.5 kDa. Based on Northern hybridization analysis, MCT3 transcript was expressed in only two tissues: RPE and choroid plexus epithelium (CPE). The choroid plexus forms a barrier between the cerebrospinal fluid and fenestrated capillaries, similar to the organization of the RPE and choroidal vessels. Immunohistochemical staining demonstrated that MCT3 was restricted to the basolateral membranes of both epithelia but was more abundant in RPE than CPE. Differences in the level of protein expression were confirmed by Western blot analysis. The cloning of MCT3 identifies a specific transporter that could regulate lactate levels in fluid-bathing neuronal tissues.
retina; lactate; transporter; blood-tissues barrier; monocarboxylate transporter
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
THE RETINAL PIGMENT EPITHELIUM (RPE) forms the outer blood-retinal barrier that controls the chemical composition of the subretinal space in much the same way that the choroid plexus epithelium (CPE) maintains the composition of the cerebrospinal fluid (CSF) (18). The basolateral surface of the RPE is in contact with the blood plasma that filters through the fenestrated capillaries in the choroid. The apical surface of the RPE is in intimate contact with the neural retina and extends processes into the subretinal space that interdigitate with photoreceptor cell outer segments. Tight junctional complexes at the lateral borders of the RPE impede the movement of even small water-soluble molecules between cells. Substances that are produced and used in large quantities, such as glucose, amino acids, and lactate, are transported into and out of the retina by the RPE (3, 21).
In retina, lactate is produced through aerobic glycolysis and utilized to fuel oxidative phosphorylation (22, 23). Glucose is transported from choroidal vessels to the subretinal space by the RPE. Müller glial cells have a limited number of mitochondria and utilize glucose to produce and release lactate into the subretinal space under aerobic conditions. Lactate is used by photoreceptor cells for oxidative phosphorylation. The Müller glial cells produce lactate, while the RPE regulates lactate levels in the subretinal space by transporting excess lactate from the retina to the choroidal venules (7, 10). A comparable mechanism has been proposed to operate in the brain where glial cell metabolism of glucose provides lactate to neurons for further metabolism (12, 15). This local control of metabolic fuels is referred to as the "lactate shuttle" (12).
In brain, the choroid plexus consists of a branched network of fenestrated capillaries ensheathed by epithelial cells that are connected by tight junctional complexes. The choroid plexus epithelium produces CSF, regulates its ionic composition, and transports micronutrients into the brain (20). Tight junctional complexes of the CPE form a barrier between the CSF and fenestrated capillaries, similar to the organization of the choroid and RPE. In contrast to the subretinal space, under normal conditions, lactate concentrations in CSF are ~1.4 mM, similar to levels found in plasma (19).
Transport of lactate, as well as pyruvate and ketone bodies across the plasma membrane of cells, is mediated by a family of proton-coupled monocarboxylate transporters (MCTs) (16). Eight members of this family have been identified in human tissues and share a 25-70% homology in their primary structure (17). MCTs share structural and functional features but differ in their temporal and spatial distribution. On the basis of their primary structure, the MCTs are predicted to have 12 membrane-spanning domains, and their NH2 and COOH termini are on the cytoplasmic side of the membrane. The membrane-spanning domains share the greatest sequence identity among the various isoforms, whereas the COOH-terminal regions are not well conserved. MCT1 is expressed in most tissues, whereas MCT2, MCT3, and MCT4 have more restricted distributions (reviewed in Refs. 5 and 6).
MCT3 regulates lactate levels in the subretinal space by transporting lactate across the basolateral membrane of RPE to the choroidal vessels (14). It may play a similar role in maintaining lactate concentrations in the CSF by transporting lactate out of the CPE. In the present study, we isolated the mouse MCT3 cDNA and characterize in detail for the first time the expression pattern of this isoform in a mammalian system.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Chemicals. All reagents were purchased from Sigma Chemical (St. Louis, MO) unless otherwise stated.
Tissues. Tissues for RNA, protein, and immunohistochemical analyses were isolated from adult and suckling C3H mice. The animals were euthanized with pentobarbital sodium (150 mg/kg body wt). Eyes were enucleated and the anterior segment was removed with a razor blade. The posterior eyecup was placed in PBS containing 15 mM EDTA and 3% sucrose. RPE or RPE/choroid were peeled off the sclera with fine forceps under a dissecting microscope. Brains were removed from the skull, and the choroid plexus was collected from the lateral and fourth ventricles. Total RNA used for cDNA cloning and Northern blot analysis was prepared from various tissues of C3H mouse using TRIzol reagent (Life Technologies, Grand Island, NY) as described elsewhere (14). Detergent-soluble lysates from RPE and choroid plexus were prepared as previously described (14).
Cloning of mouse MCT3 cDNA. Mouse MCT3 cDNA was cloned from total RNA isolated from RPE by a combination of 3'-rapid amplification of cDNA ends (RACE) and 5'-RACE, following manufacturer's instructions (Life Technologies). For the 3'-RACE, the first-strand cDNA was prepared with 3 µg of total RPE RNA and an adaptor primer 3AP (provided in the kit). cDNA was amplified with a forward primer Pr1 (5'-ggc gca cta cag ttt gag gt-3', 1009-1028, based on the first nucleotide of the coding region being nucleotide 1) and a reverse primer AUAP (abridged universal amplification primer; provided in the kit). The Pr1 primer was designed from the sequence of a mouse cDNA clone (GenBank accession no. AA190132). This clone had significant homology to the chicken MCT3 when the GenBank mouse expressed sequence tags database was queried with the chicken MCT3 cDNA sequence. The 3'-RACE amplified a 0.6-kb fragment (1009-1593) from the RPE. Primers for the 5'-RACE were designed from the sequence of the 0.6-kb fragment. The first-strand cDNA for the 5'-RACE was prepared with 1 µg of total RNA and a primer P206R (5'-act gcc atg aag act cct gc-3', 1195-1214). The cDNA was amplified sequentially with primer sets of 5AAP (abridged anchor primer; in the kit) and P123R (5'-tct tca gag cat cca cca gg-3', 1131-1150) and then AUAP and P11R (5'-tgc cat gag cac ctc aaa ct-3', 1019-1038). The coding sequence of the mouse MCT3 was confirmed by an amplification of the cDNA using primers designed from the sequences of the 5'- and 3'-RACE products.
To obtain the 5'-untranslated sequence of the MCT3 transcript expressed in the choroid plexus, 5'-RACE was performed. The first-strand cDNA was prepared with 1 µg of total RNA of mouse choroid plexus and a primer SALIM (5'-gca aag gaa gcc aga atc at-3', 295-314). The cDNA was amplified sequentially with primer sets of 5AAP and VLISS (5'-cac gag gat gct gga caa-3', 220-237) and then AUAP and LMISS (5'-gcc aac atg atg gag gac a-3', 179-197). All the RACE products were sequenced after gel purification with a QIAEX II gel purification kit (QIAGEN, Valencia, CA).Cloning of mouse MCT3 genomic DNA.
Mouse bacterial artificial chromosome (BAC) clone (54I15)
containing the mouse MCT3 was obtained by screening a mouse BAC library
(cat. no. 96040P) by PCR with a primer set of Pr1 and P206R (Research
Genetics, Huntsville, AL). Mouse MCT3 genomic DNA sequence was obtained
from both direct sequencing of a BAC DNA and sequencing PCR-amplified
fragments. The following primer sets were used to amplify the mouse
MCT3 gene: ST127 (5'-ccc taa atc cag agt cag gtc cag g-3', 114
through
90) and VLISS, LGLAL (5'-cct ggg cct agc tct caa ctt cca-3',
360-383) and Pr39R (5'-acc cac ggt tgc cat gag cac-3',
1027-1047), Pr1 and P206R, and VARP (5'-tcg tgg gct tcg tgg aca
tcg t-3', 809-830) and LAVE (5'-caa ggc cac ttc aga gcc agc
aag-3', 1171-1194). PCR products from each primer set overlapped
to at least one side of the neighboring PCR product. Primers used for
direct sequencing were INT1-86R (5'-ttc cag gtt ctg tcg ttc ctt
gct g-3'), SALIM, and P282 (5'-aga gga tgt gga ggc tga ga-3',
1290-1309).
DNA sequence analysis. DNA sequencing was done by the DNA Sequencing Facility in the Department of Genetics and Cancer Center, University of Pennsylvania, using ABI 377 and 373A stretch sequencers with Taq FS Big Dye Terminator or Dye Primer chemistry. Database searches were performed using the BLAST program provided by the National Center for Biotechnology Information server at the National Institutes of Health.
Southern blot analysis. C3H mouse genomic DNA (20 µg) was digested with BamHI or EcoRI, separated on a 1% agarose gel, and transferred to a Hybond-N nylon membrane (Amersham Pharmacia Biotech, Piscataway, NJ). The membrane was prehybridized for 4 h and hybridized overnight at 45°C to MCT3 digoxigenin-labeled riboprobe at 5 ng/ml of hybridization solution. Blots were washed twice for 5 min in 0.1% SDS/2× SSC (sodium chloride sodium citrate; 1× SSC is 0.15 M NaCl and 0.015 M sodium citrate, pH 7.0) at room temperature; once in 0.1% SDS/0.5× SSC, and once in 0.1% SDS/0.1× SSC for 20 min at 45°C. Detection procedure was the same used for Northern analysis.
Northern blot analysis. Five micrograms of total RNA was denatured with 0.5 M glyoxal and 50% dimethyl sulfoxide and separated on a 1% agarose gel in 10 mM sodium phosphate buffer (5 mM Na2HPO4 and 5 mM NaH2PO4, pH 6.5). RNA was transferred and cross-linked to a Hybond-N membrane. The membrane was prehybridized for 4 h and hybridized overnight at 65°C with an MCT3 riboprobe prepared from a 0.6-kb 3'-RACE fragment (1009-1593). Blots were washed twice at room temperature for 5 min each in 0.1% SDS/2× SSC, 20 min in 0.1% SDS/0.5× SSC, and 20 min in 0.1% SDS/0.1× SSC at 65°C and rinsed in maleate buffer (0.1 M maleic acid, pH 7.5, and 150 mM NaCl). The hybridized probe was detected with alkaline phosphatase-conjugated anti-digoxigenin antibody and Lumi-Phos 530 (Roche Molecular Biochemicals, Indianapolis, IN) as previously described (11).
Antibodies. A rabbit polyclonal antiserum to the COOH terminus of MCT3 was generated and characterized by our laboratory (14). Antibody specificity on Western blots and tissue sections was confirmed by incubating with the antibody in the presence of the competing peptide (CAVPELDHESIGGHEARGQKA). Rabbit polyclonal antibody to the COOH terminus of mouse MCT1 was a gift from Dr. Ian Simpson (Pennsylvania State University).
Immunofluorescence. Eyes and brains were fixed by immersion in 3.5% formaldehyde in PBS (pH 7.4, 4°C). Tissues were embedded in paraffin, and 6- to 8-µm sections were cut and placed on silanized slides (American Histolabs, Gaithersburg, MD). Sections of adult mouse eye and brain were also purchased from Novagen (Madison, WI). Slides were deparaffinized before use with three 5-min washes in xylene, followed by two 5-min washes in 100% ethanol. Tissues were rehydrated in a graded series of ethanol followed by H2O and PBS and were then blocked for 1 h in PBS with 5% bovine serum albumin (BSA) and 0.1% Tween 20 (pH 7.4). Samples were incubated for 1 h with primary antibodies diluted in PBS containing 1% BSA and 0.1% Tween 20. Primary antibodies were detected using Cy3-conjugated AffiniPure donkey anti-rabbit IgG (1:250; Jackson ImmunoResearch Laboratories, West Grove, PA) diluted in the same buffer as the primary antibodies. Sections were examined on a Nikon Microphot FX microscope equipped with an Optronics digital camera (Goleta, CA). The images were collected at indicated integrated digital exposure times without adjustment of brightness or contrast. Figures were prepared using Adobe Photoshop 5.5 and Adobe Illustrator 9.0.
Western blot analysis. Detergent-soluble lysates were prepared from mouse tissues as previously described (14). Protein concentrations were determined by the bicinchoninic acid assay (Pierce, Rockford, IL) with BSA as a standard. Samples (12.5 µg) were separated on 4-12% Tris-glycine SDS-polyacrylamide gradient gels (Novex, San Diego, CA) and transferred to Immobilon-P membranes (Millipore, Bedford, MA). Membranes were incubated for 1 h at room temperature in Tris-buffered saline (TBS) blocking buffer (20 mM Tris, 137 mM NaCl, pH 7.5 with 5% BSA), followed by 1 h of incubation in TBS with primary antibodies diluted 1:1,000. The secondary antibody, horseradish peroxidase-conjugated goat anti-rabbit, was diluted 1:10,000 (Bio-Rad). Enhanced chemiluminescence (ECL; Amersham Pharmacia Biotech) was used for detection.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cloning of mouse MCT3. MCT3 was initially identified in chicken RPE (13). A human ortholog was subsequently cloned (24). In both chicken and human, MCT3 is preferentially expressed in RPE. In preparation for studies of MCT3 gene deletion, in this report we characterized the molecular structure and determined the tissue distribution of mouse MCT3. Mouse MCT3 cDNA was isolated and sequenced using a combination of 3'- and 5'-RACE and RT-PCR with RPE RNA as detailed in MATERIALS AND METHODS. The resultant cDNA consisted of a 209-bp 5'-untranslated region, 1479 bp of coding sequence, and a 114-bp 3'-untranslated region. An in-frame stop codon (UGA) was present 66 bp upstream from the predicted ATG translation start site. A typical polyadenylation signal sequence, AATAAA, began 16 nucleotides upstream from an observed poly(A)+ tail. The mouse MCT3 cDNA sequence was deposited in the GenBank database (accession no. AF019111).
MCT3 cDNA had a single open reading frame encoding a protein of 492 amino acids with a calculated relative molecular weight (Mr) of 51,500 Da. Hydropathy analysis indicated that MCT3 has the same membrane topology as other members of this family (6). The derived amino acid sequence of mouse MCT3 shown in Fig. 1 was aligned with human and chicken MCT3 sequences. Among the MCT3 orthologs, mouse MCT3 shares 82% amino acid identity with the human (24), 57% with the chicken (25), and 97% with the rat (14). Sequence differences in MCT3 polypeptides from different species were found primarily in the cytoplasmic loop between the sixth and seventh membrane-spanning domains and the COOH-terminal end (Fig. 1).
|
Genomic structure of mouse MCT3.
Mouse MCT3 was shown by Southern blot analysis to be encoded by a
single gene (Fig. 2A). A BAC
clone containing the MCT3 gene was isolated and sequenced as detailed
in MATERIALS AND METHODS and deposited in GenBank under
accession no. AF178956. The structure of the gene was determined by
comparing the cDNA and genomic sequences. The MCT3 gene spans ~3.75
kb of DNA, comprising six exons and five introns. As shown in Fig.
2B, there are two 5'-noncoding exons (1a and 1b, open boxes)
and four coding exons (filled boxes). The structure of the mouse MCT3
gene is virtually identical to the human (24) and chicken
(26) MCT3 genes. The intron/exon boundaries in the coding
region of the MCT3 gene occur at the same position in mouse, human, and
chicken genes, and all conform to the GT/AG rule (Table
1) (11). All coding
sequences were spliced within glycine residues, and the amino acid
sequences at splice sites were conserved among mouse, human, and
chicken MCT3 (Table 2). Only six
nucleotide differences were found when MCT3 genomic and cDNA sequences
were compared. The cDNA has three additional nucleotides in the
5'-untranslated region, and there are three nucleotides that differ in
the coding sequence. These differences would not alter the predicted
amino acid sequence.
|
|
|
Tissue distribution of MCT3.
Expression of mouse MCT3 mRNA in various tissues was evaluated by
Northern blot analysis (Fig.
3A). An antisense RNA probe to
the 3' end of MCT3 hybridized with a single 2-kb transcript in total
RNA preparations from RPE. MCT3 transcript was not detected in total
RNA prepared from brain, heart, intestine, kidney, liver, muscle, or
neural retina. The preferential expression of MCT3 in RPE is also seen
in chicken (13).
|
Immunolocalization of MCT3 to the basolateral membrane of RPE.
Indirect immunofluorescence was used to examine cellular and
subcellular distribution of MCT3 in the eye. Sagittal sections of
paraffin-embedded adult mouse eyes were immunostained with anti-MCT3
antibody. As shown in Fig. 4B,
MCT3 immunoreactivity was present in the RPE but not in other ocular
epithelia. There was no staining in ontologically related tissues such
as the ciliary epithelium and neural retina. The bright-field
examination of the tissue section is shown in Fig. 4A.
Higher magnification of the immunostained tissue (Fig. 4D)
and bright-field examination (Fig. 4C) demonstrate that MCT3
labeling was restricted to the basolateral membrane of the RPE.
|
Immunolocalization of MCT3 to the basolateral membrane of the CPE.
The expression of MCT3 in the mouse brain was examined by
immunostaining of paraffin sections of mouse brain. As shown in Fig.
5, labeling was found in the basolateral
membrane of CPE. MCT3 is not detected in the vascular endothelium
or in the ependymal cells, which line the ventricle and are contiguous
with the CPE. Similar labeling with the MCT3 antibody was observed in
the CPE from lateral and fourth ventricles. Immunohistochemical
labeling of tissue sections of the eye and the brain suggested that
MCT3 was less abundant in the CPE than the RPE. Using integrated
digital time, we consistently found that longer exposure times were
required to detect a signal in CPE.
|
|
Immunolocalization of MCT1 in the RPE and the CPE.
The distribution of MCT1 in the RPE and the CPE was examined using
light microscopic immunohistochemistry. Previously, we showed that MCT1
immunoreactivity was abundant in the apical processes of the RPE in rat
(14). In the mouse, MCT1 was abundant in the apical
processes of the RPE (Fig. 7B,
arrow). Immunoreactivity was also detected in the retina in
photoreceptor cell inner segments, outer nuclear layer, inner plexiform
layer, and in retinal vessels. In the brain, MCT1 staining was in the
ependymal cells lining the ventricle but not in the CPE.
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Genomic cloning studies reported here demonstrate that mouse MCT3 gene is a single copy gene with a structure nearly identical to the human and chicken MCT3 genes (24, 26). Protein coding region of mouse MCT3 is distributed over four exons separated by three introns. The initial two exon/intron junctions of the MCT3 gene were located in sequences encoding transmembrane domains, with the last exon/intron splice site in a sequence encoding a hydrophilic domain. The locations of splice sites make alternative splicing in coding regions corresponding to membrane domains unlikely. In the chicken, two 5'-noncoding exons are alternatively spliced to exon 2, accounting for the two MCT3 transcripts expressed differentially during development (26). In mouse, exons 1a and 1b are spliced in tandem to exon 2, leading to only one MCT3 transcript. The 5' ends of MCT3 amplified from RPE and CPE were identical.
The genomic structure has been reported for only one other member of the MCT family, MCT8, which was originally called XPCT (4). Mouse MCT8 gene spans 125 kb, separated by five introns. The first intron is 110 kb and is responsible for the large size of the gene. The coding sequence of MCT8 is interrupted by five introns. When MCT3 and MCT8 genes are compared, the fifth exon/intron, in the eleventh transmembrane domain, is conserved (9).
The tissue distribution of MCT3 was examined using Northern blot analysis and immunohistochemical localization. Both MCT3 transcript and protein were expressed preferentially in RPE and CPE, but not in other blood-tissue barriers. Comparable levels of MCT3 transcript were detected in RPE and CPE, but there was disparity in the amount of protein expressed in the two tissues. This suggests that expression of MCT3 in the CPE may be regulated at the level of translation.
The outer retina is metabolically active and converts a large fraction of glucose into lactate, even in the presence of oxygen (1, 23). Lactate concentrations in the subretinal space are high relative to lactate levels in the blood (~1 mM; 13 mM near the outer limiting membrane to 3.8 mM near the surface of the RPE) (1). Physiological studies have shown that lactate is transported from the subretinal space to the choroidal venules by the RPE (2). In the present study, we have shown that the RPE expresses two MCTs (MCT1 and MCT3) that were polarized to distinct membrane domains; MCT1 in the apical membrane, and MCT3 in the basolateral membrane. The coordinated activity of these two transporters could regulate the transepithelial movement of lactate out of the retina. Whereas the RPE cells express two MCT isoforms, the GLUT-1 glucose transporter is expressed on both the apical and basolateral membranes of the RPE (8, 21).
The choroid plexus forms a barrier between the CSF and fenestrated capillaries, similar to the organization of the choroid and RPE. In contrast to the high concentration of lactate in subretinal space, under normal conditions, lactate concentrations in CSF are about 1.4 mM, similar to levels found in plasma (20). MCT1 and MCT3 transcripts were both detected in RNA prepared from choroid plexus. However, MCT1 was not detected in the CPE by immunofluorescence, and MCT3 was expressed, but at lower levels than in the RPE.
In summary, the mouse MCT3 gene has been sequenced and is structurally identical to the chicken and the human MCT3 genes. Expression of the MCT3 transcript and protein is limited to two structurally and functionally similar tissues, the RPE and the CPE. MCT3 was not detected in other blood-tissue barriers such as testis, placenta, and ciliary epithelium, suggesting MCT3 has a specialized role in regulating lactate levels in fluid-bathing neuronal tissues.
![]() |
ACKNOWLEDGEMENTS |
---|
We are grateful to Dr. Evelyn F. Grollman for helpful discussions and careful reading of the manuscript.
![]() |
FOOTNOTES |
---|
This study was supported, in part, by National Eye Institute Grant EY-12042 and by the Eye Research Institute, Philadelphia, PA.
Address for reprint requests and other correspondence: N. J. Philp, Dept. of Pathology, Anatomy, and Cell Biology, Jefferson Medical College, Thomas Jefferson Univ., 1020 Locust St., Philadelphia, PA 19107 (E-mail: nancy.philp{at}mail.tju.edu).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 21 August 2000; accepted in final form 4 December 2000.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Adler, AJ,
and
Southwick RE.
Distribution of glucose and lactate in the interphotoreceptor matrix.
Ophthalmic Res
24:
243-252,
1992[ISI][Medline].
2.
Alm, A,
and
Tornquist P.
Lactate transport through the blood-retinal and the blood-brain barrier in rats.
Ophthalmic Res
17:
181-184,
1985[ISI][Medline].
3.
Bok, D.
The retinal pigment epithelium: a versatile partner in vision.
J Cell Sci Suppl
17:
189-195,
1993[Medline].
4.
Debrand, E,
Heard E,
and
Avner P.
Cloning and localization of the murine Xpct gene: evidence for complex rearrangements during the evolution of the region around the Xist gene.
Genomics
48:
296-303,
1998[ISI][Medline].
5.
Halestrap, AP,
and
Price NT.
The proton-linked monocarboxylate transporter (MCT) family: structure, function and regulation.
Biochem J
343:
281-299,
1999[ISI][Medline].
6.
Juel, C,
and
Halestrap AP.
Lactate transport in skeletal muscle - role and regulation of the monocarboxylate transporter.
J Physiol (Lond)
517:
633-642,
1999
7.
Kenyon, E,
Yu K,
la Cour M,
and
Miller SS.
Lactate transport mechanisms at apical and basolateral membranes of bovine retinal pigment epithelium.
Am J Physiol Cell Physiol
267:
C1561-C1573,
1994
8.
Kumagai, AK,
Glasgow BJ,
and
Pardridge WM.
GLUT1 glucose transporter expression in the diabetic and nondiabetic human eye.
Invest Ophthalmol Vis Sci
35:
2887-2894,
1994[Abstract].
9.
Lafreniere, RG,
Carrel L,
and
Willard HF.
A novel transmembrane transporter encoded by the XPCT gene in Xq13.2.
Hum Mol Genet
3:
1133-1139,
1994[Abstract].
10.
Lin, H,
la Cour M,
Andersen MV,
and
Miller SS.
Proton-lactate cotransport in the apical membrane of frog retinal pigment epithelium.
Exp Eye Res
59:
679-688,
1994[ISI][Medline].
11.
Padgett, RA,
Grabowski PJ,
Konarska MM,
Seiler S,
and
Sharp PA.
Splicing of messenger RNA precursors.
Annu Rev Biochem
55:
1119-1150,
1986[ISI][Medline].
12.
Pellerin, L,
Pellegri G,
Bittar PG,
Charnay Y,
Bouras C,
Martin JL,
Stella N,
and
Magistretti PJ.
Evidence supporting the existence of an activity-dependent astrocyte-neuron lactate shuttle.
Dev Neurosci
20:
291-299,
1998[ISI][Medline].
13.
Philp, N,
Chu P,
Pan TC,
Zhang RZ,
Chu ML,
Stark K,
Boettiger D,
Yoon H,
and
Kieber-Emmons T.
Developmental expression and molecular cloning of REMP, a novel retinal epithelial membrane protein.
Exp Cell Res
219:
64-73,
1995[ISI][Medline].
14.
Philp, NJ,
Yoon H,
and
Grollman EF.
Monocarboxylate transporter MCT1 is located in the apical membrane and MCT3 in the basal membrane of rat RPE.
Am J Physiol Regulatory Integrative Comp Physiol
274:
R1824-R1828,
1998
15.
Poitry-Yamate, CL,
Poitry S,
and
Tsacopoulos M.
Lactate released by Muller glial cells is metabolized by photoreceptors from mammalian retina.
J Neurosci
15:
5179-5191,
1995[Abstract].
16.
Poole, RC,
and
Halestrap AP.
Transport of lactate and other monocarboxylates across mammalian plasma membranes.
Am J Physiol Cell Physiol
264:
C761-C782,
1993
17.
Price, NT,
Jackson VN,
and
Halestrap AP.
Cloning and sequencing of four new mammalian monocarboxylate transporter (MCT) homologues confirms the existence of a transporter family with an ancient past.
Biochem J
329:
321-328,
1998[ISI][Medline].
18.
Rizzolo, LJ.
Polarity and the development of the outer blood-retinal barrier.
Histol Histopathol
12:
1057-1067,
1997[ISI][Medline].
19.
Saunders, NR,
Habgood MD,
and
Dziegielewska KM.
Barrier mechanisms in the brain, I. Adult brain.
Clin Exp Pharmacol Physiol
26:
11-19,
1999[ISI][Medline].
20.
Spector, R,
and
Johanson CE.
The mammalian choroid plexus.
Sci Am
261:
68-74,
1989[ISI][Medline].
21.
Sugasawa, K,
Deguchi J,
Okami T,
Yamamoto A,
Omori K,
Uyama M,
and
Tashiro Y.
Immunocytochemical analyses of distributions of Na, K-ATPase and GLUT1, insulin and transferrin receptors in the developing retinal pigment epithelial cells.
Cell Struct Funct
19:
21-28,
1994[ISI][Medline].
22.
Tornquist, P,
and
Alm A.
Retinal and choroidal contribution to retinal metabolism in vivo. A study in pigs.
Acta Physiol Scand
106:
351-357,
1979[ISI][Medline].
23.
Wang, L,
Tornquist P,
and
Bill A.
Glucose metabolism in pig outer retina in light and darkness.
Acta Physiol Scand
160:
75-81,
1997[ISI][Medline].
24.
Yoon, H,
Donoso LA,
and
Philp NJ.
Cloning of the human monocarboxylate transporter MCT3 gene: localization to chromosome 22q12.3-q132.
Genomics
60:
366-370,
1999[ISI][Medline].
25.
Yoon, H,
Fanelli A,
Grollman EF,
and
Philp NJ.
Identification of a unique monocarboxylate transporter (MCT3) in retinal pigment epithelium.
Biochem Biophys Res Commun
234:
90-94,
1997[ISI][Medline].
26.
Yoon, H,
and
Philp NJ.
Genomic structure and developmental expression of the chicken monocarboxylate transporter MCT3 gene.
Exp Eye Res
67:
417-424,
1998[ISI][Medline].