Abstract
We have recently demonstrated substantial stereospecific nuclear/cytosolic free triidothyronine (T 3) gradients within T 3 responsive rat tissues in situ. These studies have now been extendeb to examine T 3 transport in a rat pituitary tumor cell line, GH1. L-T 3 had a 7.6-fold higner affinity for the nuclear receptor when assayed in whole cell incubations in comparison to isolated nuclei, though D-T 3 affinity was not altered under these conditions. An apparently higher number of receptors for D-T 3 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-T 3 (1.65) but a reverse ratio for D-T 3 (0.46). The nuclei were able to concentrate both enantiomers, though stereospecificity was maintained (nucleus/cytosol, L-T 3 4.5, D-T 3 1.7). Transport of L-T 3 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.
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