title: Uptake of L-triiodothyronine sulphate by human choriocarcinoma cell line, JAr.
abstract: This study investigated uptake of triiodothyronine sulphate (T3S) and interactions between uptake of T3S and triiodothyronine (T3) using the human choriocarcinoma cell line (JAr) as a model of placental transport. Cells were incubated at 37 degrees C with 30 pM 125I-T3 for 2 min with unlabelled T3 (0-30 microM) or T3S (0-1 mM). Addition of an excess unlabelled T3 (30 microM) or T3S (1 mM) reduced the initial rate of 125I-T3 uptake by 69.3+/-3.6 per cent (P<0.0001) and 52.9+/-7.8 per cent (P<0.0001), respectively. The calculated Michaelis constant (Km) for T3 uptake was 0.378+/-0.133 microM (n = 3) with a corresponding maximum velocity (Vmax) of 15.4+/-6.9 pmol/min/mg protein. Uptake of 125I-T3 was inhibited in a dose-dependent way by the addition of unlabelled T3S (0-1 mM). The calculated inhibition constant (Ki) for the inhibition of 125I-T3 uptake by T3S was 121.8+/-35.2 microM (n = 6). Saturable uptake of 125I-T3S by JAr cells was negligible. The T3S preparation incubated with the cells contained about 0.1 per cent T3, sufficient to explain the apparent inhibition of 125I-T3 uptake by unlabelled T3S. These results suggest that, in contrast to T3 uptake in these cells, JAr cells do not have a saturable uptake mechanism for T3S, and that T3S does not interact with the T3 transporter in these cells.
authors: Division of Chemical Pathology, Queensland Health Pathology Service, Royal Brisbane Hospital Campus, Australia. bernusi@health.qld.gov.au
authors: I
authors: I
authors: Bernus
authors: A M
authors: AM
authors: Mitchell
authors: S W
authors: SW
authors: Manley
authors: R H
authors: RH
authors: Mortimer
mesh_terms: D001692:Biological Transport; D002822:Choriocarcinoma / Q000378:metabolism*; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D014284:Triiodothyronine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014594:Uterine Neoplasms / Q000378:metabolism*
chemical_list: D007457:Iodine Radioisotopes; D014284:Triiodothyronine; C037673:triiodothyronine sulfate