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  • Title: Uptake of L-triiodothyronine sulphate by human choriocarcinoma cell line, JAr.
    Author: Bernus I, Mitchell AM, Manley SW, Mortimer RH.
    Journal: Placenta; 1999; 20(2-3):161-5. PubMed ID: 10195736.
    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.
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