Thyroid hormone effects on the proton permeability of rat liver mitochondria.

The effect of thyroid status on passive permeability of liver mitochondrial inner membrane was studied in euthyroid (EU), hyperthyroid (HYPER), hypothyroid (HYPO) rats and hypothyroid rats treated with a single dose of 3,3',5-triiodothyronine (HYPO + T3). Respiration was titrated with uncoupler and plotted against uncoupler concentration to calculate proton permeability. The passive permeability was the same in EU, HYPER, and HYPO + T3 rats, but was significantly lower in HYPO mitochondria. The State IV respiration rates were the same as the oligomycin-inhibited rats for EU, HYPO and HYPO + T3 rats, but in HYPER rats the oligomycin rate was less than the State IV rate. The data show that hypothyroid mitochondria have decreased permeability of the inner membrane which can be normalized by a single dose of T3. Hyperthyroid mitochondria show increased oligomycin-sensitive ATPase activity in State IV, a possible mechanism of the enhanced respiratory rate.