Fig. 1.
Nuclear and cytosolic 125I-T3/131I-T3 (triiodothyronine) ratio or total 131I-T3 in C2C12 cells after overnight incubation with 125I-T4 (thyroxine) and 131I-T3. Proliferating (prolif) and differentiated (differ) C2C12 cells were incubated in physiological concentrations of free 131I-T3 and 125I-T4 in DMEM containing 0.1% BSA and treated with vehicle or 30 nM reverse (r)T3 to block type II deiodinase (D2). Nuclear extracts (A) and cytosol fractions (B) were isolated, and labeled T3 was identified by paper chromatography. The basal ratio of 125I-T3(T4) to 131I-T3(T3) in proliferating C2C12 cells treated with vehicle were arbitrarily set as 1 (1st column on the left), and the remaining results were normalized to that value. 131I-T3 in nuclear extracts (C) or cytosol (D) were normalized as in A and B. Data are means ± SE of triplicates of 3 independent experiments. **P < 0.01; ***P < 0.001; ns, not significant.