The early triiodothyronine-induced changes in state IV respiration is not regulated by the proton permeability of the mitochondrial inner membrane.

: The time course of changes in mitochondrial respiration, alpha-glycerophosphate dehydrogenase activity, and inner membrane proton permeability and the effects of protein synthesis inhibition was determined in hypothyroid rats treated with triiodothyronine. Respiratory rates, alpha-glycerophosphate dehydrogenase activity and proton permeability were decreased in hypothyroid rats and rose to euthyroid levels 9-12 hours after triiodothyronine treatment. Some rats received actinomycin D with the hormone to inhibit protein synthesis. Sixteen hours after actinomycin D and hormone treatment, the increases in respiratory rates and in alpha-glycerophosphate dehydrogenase activity, were completely inhibited. However, actinomycin D did not inhibit the increase in the membrane's permeability.