title: Uptake of thyroxine in the human choriocarcinoma cell line JAR.
abstract: We have studied the uptake of 125I-thyroxine (125I-T4) in the human choriocarcinoma cell line JAR. Uptake of 125I-T4 was time-dependent, stereospecific and reversible, with a saturable component of 33% after 120 min of incubation. Kinetic analysis of the initial specific uptake rates indicated the presence of a single uptake process with a Michaelis constant of 59.4 +/- 13.9 nM (n = 12) and maximum velocity of 0.29 +/- 0.06 pmol/min per mg protein. Uptake was dependent on intracellular energy as, in the presence of 2 nM potassium cyanide, saturable uptake was reduced to 60.6 +/- 8.5% (n = 4) of control uptake. Uptake was also temperature-dependent. Saturable 125I-T4 uptake after 60 min of incubation was 26.1 +/- 3.0% at 25 degrees C (n = 6) and 27.3 +/- 5.7% at 4 degrees C of control uptake at 37 degrees C. Ouabain did not inhibit 125I-T4 uptake indicating that the uptake was independent of the Na+ gradient across the cell membrane. Although T4 uptake was stereospecific, as D-T4 failed to inhibit 125I-L-T4 uptake, it was not specific for T4, as tri-iodothyronine (T3) and reverse T3 also inhibited 125I-T4 uptake. We conclude that JAR cells have a saturable, stereospecific and reversible membrane transport mechanism for T4 which is dependent on intracellular energy, but independent of the Na+ gradient across the cell membrane.
authors.affiliation: Conjoint Endocrine Laboratory, Royal Brisbane Hospital, Queensland, Australia.
authors.forename: A M
authors.initials: AM
authors.lastname: Mitchell
authors.forename: S W
authors.initials: SW
authors.lastname: Manley
authors.forename: E J
authors.initials: EJ
authors.lastname: Payne
authors.forename: R H
authors.initials: RH
authors.lastname: Mortimer
mesh_terms: D002822:Choriocarcinoma / Q000378:metabolism*; D005260:Female; D006801:Humans; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D013696:Temperature; D013974:Thyroxine / Q000378:metabolism* / Q000494:pharmacology; D013997:Time Factors; D014284:Triiodothyronine / Q000494:pharmacology; D014285:Triiodothyronine, Reverse / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014594:Uterine Neoplasms / Q000378:metabolism*
chemical_list: D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D010042:Ouabain; D013974:Thyroxine