title: Sodium-dependent carnitine transport in human placental choriocarcinoma cells.
abstract: The JAR human placental choriocarcinoma cells were found to transport carnitine into the intracellular space by a Na(+)-dependent process. The transport showed no requirement for anions. The Na+-dependent process was saturable and the apparent Michaelis-Menten constant for carnitine was 12.3 +/- 0.5 microM. Na+ activated the transport by increasing the affinity of the transport system for carnitine. The transport system specifically interacted with L-carnitine, D-carnitine, acetyl-DL-carnitine and betaine. 6-N-Trimethyllysine and choline had little or no effect on carnitine transport. Of the total transport measured, transport into the intracellular space represented 90%. Plasma membrane vesicles prepared from JAR cells were found to bind carnitine in a Na(+)-dependent manner. The binding was saturable with an apparent dissociation constant of 0.66 +/- 0.08 microM. The binding process was specific for L-carnitine, D-carnitine, acetyl-DL-carnitine, and betaine. 6-N-Trimethyllysine and choline showed little or no affinity. It is concluded that the JAR cells express a Na(+)-dependent high-affinity system for carnitine transport and that the Na(+)-dependent high-affinity carnitine binding detected in purified JAR cell plasma membrane vesicles is possibly related to the transmembrane transport process.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912-2100, USA.
authors.forename: P D
authors.initials: PD
authors.lastname: Prasad
authors.forename: W
authors.initials: W
authors.lastname: Huang
authors.forename: S
authors.initials: S
authors.lastname: Ramamoorthy
authors.forename: A L
authors.initials: AL
authors.lastname: Carter
authors.forename: F H
authors.initials: FH
authors.lastname: Leibach
authors.forename: V
authors.initials: V
authors.lastname: Ganapathy
mesh_terms: D001665:Binding Sites; D001692:Biological Transport; D002331:Carnitine / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002822:Choriocarcinoma / Q000378:metabolism*; D005260:Female; D006801:Humans; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D012964:Sodium / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014594:Uterine Neoplasms / Q000378:metabolism*
chemical_list: D012964:Sodium; D002331:Carnitine