Altered relationship between protonmotive force and respiration rate in non‐phosphorylating liver mitochondria isolated from rats of different thyroid hormone status

Abstract

We have determined the relationship between rate of respiration and protonmotive force in oligomycininhibited liver mitochondria isolated from euthyroid, hypothyroid and hyperthyroid rats. Respiration ratc was titrated with the respiratory-chain inhibitor malonate. At any given respiration rate mitochondria isolated from hypothyroid rats had a protonmotive force greater than mitochondria isolated from euthyroid controls, and mitochondria isolated from hyperthyroid rats had a protonmotive force less than mitochondria isolated from euthyroid controls, In the absence of malonate mitochondrial respiration rate increased in the order hypothyroid < euthyroid < hyperthyroid, while protonmotive force increased in the order hyperthyroid < euthyroid < hypothyroid. These findings are consistent with a thyroid-hormone-induced increase in the proton conductance of the inner mitochondrial membrane or a decrease in the H+/O ratio of the respiratory chain at any given protonmotive force. Thus the altered proton conductance or H+/O ratio of mitochondria isolated from rats of different thyroid hormone status controls the respiration rate required to balance the backflow of protons across the inner mitochondrial membrane. We discuss the possible relevance of these findings to the control of state 3 and state 4 respiration by thyroid hormone.Mitochondria isolated from hypothyroid rats chardcteristically show decreased state 4 and state 3 (nomenclature of Chance and Williams [I]) respiration rates relative to control rat mitochondria, while mitochondria from hyperthyroid rats show elevated statc 4 and state 3 respiration rates (see [2] for a review). The stimulation of state 4 respiration rate following administration of tri-iodo-L-thyronine to hypothyroid rats is not a consequence of increased ATP turnover as the respiration rates of these mitochondria remains faster (relative to mitochondria from hypothyroid rats) in the presence of oligomycin to inhibit the ATP synthase [3].The control of non-phosphorylating respiration (i. e. in the presence of oligomycin) is relatively simple. As Ap rises the permeability of the inner mitochondrial membrane to protons increases rapidly above about 130 mV Ahhrcviatians. Albumin, bovine serum albumin; FCCP, carbonyl cyanidc p-trifluoromethoxyphenylhydrazone; Me4N+, tetramethylammonium; Ph3MeP*, mcthyltriphenylphosphonium cation; SEM, standard error of the mean; H+/O, number of protons rclcased to the external bulk phase/oxygen atom reduced; Ap, difference in electrical potential across the mitochondrial inner membrane; A p , protonmotive force across the mitochondrial inner membrane, ApH, pH gradient across the mitochondrial inner membrane.istics of the mitochondrial inner membrane to protons (leak), the kinetic behaviour of the proton-pumping respiratory chain and the H+/O ratio of the respiratory chain. In the present analysis we do not discriminate between a decrease in stoichiometry and an increase in the proton permeability of the mitochondrial inner membrane. The effect of either of these ...

Mechanisms of the Deleterious Effects of Tamoxifen on Mitochondrial Respiration Rate and Phosphorylation Efficiency

“…We adopted the approach developed by Brand (1990) that is ideally suited to analyze compounds with pleiotropic effects on oxidative phosphorylation and has been used to investigate the mechanism of thyroid hormones (Hafner et al, 1988(Hafner et al, , 1989, glucagon , butylated hydroxyanisole (Fusi et al, 1992), and DDE (Ferreira et al, 1997) and to study functional variations in the liver mitochondria compartment in 25-and 60-day-old rats (Lionetti et al, 1998). The putative proton leaks induced by TAM through the mitochondrial inner membrane were investigated in nonphosphorylating mitochondria titrated with malonate, a respiratory inhibitor, and ⌬⌿ (⌬⌿ equals ⌬p in the used experimental conditions) was plotted against the respiration rate (Fig.…”

The significance and mechanism of mitochondrial proton conductance

“…Thyroid hormones do alter the fractional contribution of proton leak to hepatocyte respiration and cause cellular respiration rate to change. Hyperthyroid rat liver mitochondria have ®ve times higher proton conductance than hypothyroids, 32 and this causes half of the difference in hepatocyte respiration. 33 Similarly, metabolic rates in hibernation and aestivation can be reduced six-fold or more, and mitochondrial proton leak may decrease here too.…”

Mitochondrial Bioenergetics, Diabetes, and Aging: Top-Down Analysis Using the Diabetic Goto-Kakizaki (GK) Rat as a Model

“…In this context, the oxidative phosphorylation system is conceptually divided into two subsystems: one producing the protonmotive force ( p) (respiratory chain, succinate dehydrogenase, and dicarboxylate carrier) and another that consumes the p (adenine nucleotides and phosphate carriers, ATP synthase, and proton leak) (Hafner et al 1988). These two component systems interact via p, which has been assumed to be entirely delocalized.…”

“…These two component systems interact via p, which has been assumed to be entirely delocalized. The overall response of the p generators to p can be obtained from an uncoupler titration of respiration rate versus p; the overall response of p consumers to p can be obtained from an inhibitor titration of respiration rate versus p (Hafner et al 1988).…”