The rapid alteration by tri-iodo-L-thyronine in vivo of both the ADP/O ratio and the apparent H+/O ratio in hypothyroid-rat liver mitochondria.
Mitochondria from the livers of thyroidectomized rats have a lowered ADP/O ratio, which can be restored to normal within 15 min after intravenous injection of a near-physiological dose of tri-iodothyronine. Thyroidectomy lowered the measured delta pH, which appears to be compensated by a rise (not statistically significant) in the membrane potential, so that the protonmotive force is unaltered. A simple simulation technique is described for use in estimating H+/O ratios by the oxygen-pulse technique, which circumvents the problem that this ratio can be seriously underestimated because of re-uptake of protons from the bulk phase by the mitochondria before their expulsion is complete. By this procedure the H+/O ratio of hypothyroid mitochondria is shown to be lowered by the same factor as the ADP/O ratio, and both these ratios are very rapidly restored in parallel by hormone administration. Although these findings could be consistent with a proposal that tri-iodothyronine rapidly modulates by some mechanism the efficiency of the respiratory-chain-linked proton pumps, the kinetic properties of the proton exchange suggest that the bulk-phase protons measured may not reflect faithfully those that drive the ATP synthetase.
D000244:Adenosine Diphosphate / Q000378:metabolism*; D000818:Animals; D006863:Hydrogen-Ion Concentration; D007037:Hypothyroidism / Q000378:metabolism*; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism*; D011522:Protons; D051381:Rats; D013965:Thyroidectomy; D014284:Triiodothyronine / Q000494:pharmacology*
D011522:Protons; D014284:Triiodothyronine; D000244:Adenosine Diphosphate; D010100:Oxygen