Uptake of thyroxine in the human choriocarcinoma cell line JAR

• Published in: Journal of endocrinology Vol. 146; no. 2; pp. 233 - 238
• Main Authors: MITCHELL, A. M, MANLEY, S. W, PAYNE, E. J, MORTIMER, R. H
• Format: Journal Article
• Language: English
• Published: Colchester BioScientifica 01.08.1995; Portland Press
• Subjects: Biological and medical sciences; Choriocarcinoma - metabolism; Female; Fundamental and applied biological sciences. Psychology; Hormones. Regulation; Humans; Kinetics; Ouabain - pharmacology; Temperature; Thyroid. Parathyroid. Ultimobranchial body; Thyroxine - metabolism; Thyroxine - pharmacology; Time Factors; Triiodothyronine - pharmacology; Triiodothyronine, Reverse - pharmacology; Tumor Cells, Cultured; Uterine Neoplasms - metabolism; Vertebrates: endocrinology; Human; Trophoblaste; Cell line; Biological transport; Thyroxine; Chorioepithelioma; Thyroid hormone; Uptake
• ISSN: 0022-0795; 1479-6805
• DOI: 10.1677/joe.0.1460233

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 mm 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 °C (n=6) and 27·3 ± 5·7% at 4 °C of control uptake at 37 °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. Journal of Endocrinology (1995) 146, 233–238