Molecular cloning and characterization of high-affinity carnitine transporter from rat intestine.
Carnitine is an essential component for mitochondrial beta-oxidation of fatty acid. Using the degenerate primers designed for organic anion transporters and an organic cation transporter, we isolated a novel cDNA encoding a carnitine transporter (CT1) from rat intestine. CT1 encodes a 557-amino-acid protein with 12 putative membrane-spanning domains. When expressed in Xenopus oocytes, CT1 mediated a high-affinity transport of L-carnitine (Km = 25 microM). The replacement of extracellular sodium with Li reduced CT1-mediated L-carnitine uptake to 19.8%. CT1 did not transport typical substrates for either organic anion or organic cation transporters, such as p-aminohippurate and tetraethylammonium. Octanoylcarnitine, acetylcarnitine, and gamma-butyrobetaine showed potent inhibitory effects on CT1-mediated L-carnitine uptake; betaine and d-carnitine showed moderate inhibition. CT1 mRNA was strongly expressed in the testis, colon, kidney, and liver and weakly in the skeletal muscle, placenta, small intestine, and brain. No CT1 expression was detected in the heart, spleen, or lung. The present study provides the molecular basis of carnitine transport in the body.
Sekine
T
T
Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Tokyo, Mitaka, Japan.
Kusuhara
H
H
Utsunomiya-Tate
N
N
Tsuda
M
M
Sugiyama
Y
Y
Kanai
Y
Y
Endou
H
H
D000595:Amino Acid Sequence; D000818:Animals; D000838:Anions / Q000378:metabolism; D002331:Carnitine / Q000378:metabolism*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D002412:Cations / Q000378:metabolism; D003001:Cloning, Molecular; D017124:Conserved Sequence; D017931:DNA Primers; D005260:Female; D015723:Gene Library; D007413:Intestinal Mucosa / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D027701:Organic Cation Transport Proteins; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D000074058:Solute Carrier Family 22 Member 5; D013379:Substrate Specificity; D014982:Xenopus laevis
D000838:Anions; D002352:Carrier Proteins; D002412:Cations; D017931:DNA Primers; D027701:Organic Cation Transport Proteins; D011994:Recombinant Proteins; C115441:Slc22a5 protein, rat; D000074058:Solute Carrier Family 22 Member 5; D002331:Carnitine