Ion transport in liver mitochondria from normal and thyroxine-treated rats.

Liver mitochondria isolated from rats 24 h after a single subcutaneous injection of 8 mg thyroxine per kilogram body weight were compared with those isolated from control rats that received injections of isotonic saline at the same time. The mitochondria isolated from the thyroxine-treated rats show higher rates of energy-dependent K+ and phosphate accumulation than those from control animals. It was also found that mitochondria from the hormone-treated animals required a larger addition of Ca2+/mg mitochondrial protein in order to uncouple oxidative phosphorylation, and showed smaller tendency to swell in vitro under energizing conditions. The data obtained on ion movements support previous observations that the stimulation of the basal rate of mitochondrial respiration by thyroxine is associated with an increase in the transmembrane protonic electrochemical potential difference, and indicate the in vivo the hormone raises the intramitochondrial concentration of K+ and phosphate.