Regular Article
Functional Characterization of the Carnitine Transporter Defective in Primary Carnitine Deficiency

https://doi.org/10.1006/abbi.1999.1118Get rights and content

Abstract

Primary carnitine deficiency is an autosomal recessive disorder caused by defective carnitine transport which impairs fatty acid oxidation and manifests as nonketotic hypoglycemia or skeletal or heart myopathy. Here we report the functional characterization of this transporter in human fibroblasts. Carnitine enters normal cells by saturable and unsaturable routes, the latter corresponding to Na+-independent uptake. Saturable carnitine transport was absent in cells from patients with primary carnitine deficiency. In control cells, saturable carnitine transport was energized by the electrochemical gradient of Na+. Carnitine uptake was not inhibited by amino acid substrates of transport systems A, ASC, and XAG, but was inhibited competitively (in potency order) by butyrobetaine > carnitine > palmitoylcarnitine = acetylcarnitine > betaine. Carnitine uptake was also noncompetitively inhibited by verapamil and quinidine, inhibitors of the multidrug resistance family of membrane transporters, suggesting that the carnitine transporter may share a functional motif with this class of transporters. A high-affinity carnitine transporter was present in kidney 293 cells, but not in HepG2 liver cells, whose carnitine transporter had aKmin the millimolar range. These result indicate the presence of multiple types of carnitine transporters in human cells.

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    1

    To whom correspondence should be addressed at Department of Pediatrics, Division of Medical Genetics, Emory University, 2040 Ridgewood Dr., Atlanta, GA 30322. Fax: (404) 727 9398. E-mail:[email protected].

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