Stereospecific transport of triiodothyronine to cytoplasm and nucleus in GH1 cells.
We have recently demonstrated substantial stereospecific nuclear/cytosolic free triiodothyronine (T3) gradients within T3 responsive rat tissues in situ. These studies have now been extended to examine T3 transport in a rat pituitary tumor cell line, GH1. L-T3 had a 7.6-fold higher affinity for the nuclear receptor when assayed in whole cell incubations in comparison to isolated nuclei, though D-T3 affinity was not altered under these conditions. An apparently higher number of receptors for D-T3 was explained by racemic contamination of the isotopes used. Measurement of free hormone concentration ratios for both enantiomers revealed a small step up from medium to cytosol for L-T3 (1.65) but a reverse ratio for D-T3 (0.46). The nuclei were able to concentrate both enantiomers, though stereospecificity was maintained (nucleus/cytosol, L-T3, 4.5, D-T3 1.7). Transport of L-T3 at both boundaries could be inhibited by monodansylcadaverine. Thus, stereospecific transport functions are found within GH1 cells, though the magnitude of the free nucleus/cytosol gradient is reduced from those seen in rat tissues in situ.
D000818:Animals; D001693:Biological Transport, Active; D002103:Cadaverine / Q000031:analogs & derivatives / Q000494:pharmacology; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D008433:Mathematics; D010911:Pituitary Neoplasms; D011190:Potassium Cyanide / Q000494:pharmacology; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D011988:Receptors, Thyroid Hormone; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014284:Triiodothyronine / Q000378:metabolism*
D011956:Receptors, Cell Surface; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine; C008542:monodansylcadaverine; D002103:Cadaverine; D011190:Potassium Cyanide