Calcium uptake by liver mitochondria from hypothyroid rats is inhibited in vitro by triiodothyronine

The rate of Ca2+ uptake by liver mitochondria from hypothyroid and euthyroid rats was determined as a function of the mitochondrial membrane potential (delta psi). At large values of delta psi Ca2+ uptake was a linear function of delta psi and its dependence on delta psi was the same in mitochondria from euthyroid and hypothyroid rats. However, at small values of delta psi the rates of Ca2+ uptake for mitochondria from euthyroid or hypothyroid rats deviated slightly from each other. Triiodothyronine (T3), at a concentration of 10 nM, inhibited the rate of Ca2+ uptake in vitro, suggesting that T3 in vivo may regulate mitochondrial Ca2+ transport and thus alter the matrix free Ca2+ concentration, which has control over respiration.