Lack of membrane transport of l-thyroxine sulphate in the human choriocarcinoma cell line, JAr.
We examined uptake of l -thyroxine sulphate (T(4)S) and possible interactions between T(4)S and thyroxine (T(4)) uptake in the choriocarcinoma cell line JAr. Cells were incubated with 50 p m(125)I-T(4)S in the absence (total uptake) and in the presence (non-specific uptake) of 10 microm T(4)S. Cells were also incubated at 37 degrees C for 2 min with 50 p m(125)I-T(4)in the presence of an increasing amount of unlabelled T(4)(0-10 microm) or T(4)S (0-30 microm). There was negligible total uptake of(125)I-T(4)S (1.14+/-0. 05 fmol/mg cellular protein, mean+/-sem) and no specific uptake after 120 min incubation. Minor inhibition of(125)I-T(4)uptake by T(4)S could be explained entirely by a low level of residual T(4)(0. 2 per cent) in the T(4)S preparation. These findings indicate that T(4)S does not share the T(4)membrane transporter.
Bernus
I
I
Conjoint Endocrine Laboratory, Clinical Research Centre, RBH Research Foundation and Division of Chemical Pathology, Queensland Health Pathology Service, Royal Brisbane Hospital Campus, Brisbane, Queensland, Australia. irenB@qimr.edu.au
Mitchell
A M
AM
Manley
S W
SW
Mortimer
R H
RH
D001693:Biological Transport, Active; D002462:Cell Membrane / Q000378:metabolism; D002822:Choriocarcinoma / Q000378:metabolism*; D005260:Female; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D013974:Thyroxine / Q000031:analogs & derivatives* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014594:Uterine Neoplasms / Q000378:metabolism*
C045736:thyroxine sulfate; D013974:Thyroxine