Abstract
Carnitine is an essential component for mitochondrial β-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 inXenopusoocytes, CT1 mediated a high-affinity transport ofl-carnitine (Km= 25 μM). The replacement of extracellular sodium with Li reduced CT1-mediatedl-carnitine uptake to 19.8%. CT1 did not transport typical substrates for either organic anion or organic cation transporters, such asp-aminohippurate and tetraethylammonium. Octanoylcarnitine, acetylcarnitine, and γ-butyrobetaine showed potent inhibitory effects on CT1-mediatedl-carnitine uptake; betaine andd-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.
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