Inhibition of nuclear binding of triiodothyronine by antimycin A in cultured human fibroblasts.

We have tested the effects of several cell inhibitors on cell and nuclear content of T3 at equilibrium in cultured human fibroblasts. Monodansylcadaverine and colchicine inhibited in parallel, and near to the same extent, cell and nuclear content of T3. Antimycin A did not interfere with cell accumulation of T3 but induced a 10-fold decrease of nuclear T3. This effect was due to a decrease of the apparent affinity constant of the T3 nuclear receptor. Other metabolic inhibitors such as sodium azide or potassium cyanide were without effects. It is suggested that antimycin A blocks a nuclear T3 concentrating mechanism which maintains a gradient of free T3 between the nucleus on the one hand, and the cytosol and plasma, on the other.