Thyroid hormone may induce changes in the concentration of the mitochondrial calcium uniporter

We explored the possibility that the hormone 3,3',5-tri-iodothyronine can regulate the biosynthesis of the mitochondrial calcium uniporter. To meet this objective experiments on Ca(2+) transport, and binding of the specific inhibitor Ru(360) were carried out in mitochondria isolated from euthyroid, hyperthyroid and hypothyroid rats. It was found that V(max) for Ca(2+) transport increased from 11.67+/-0.8 in euthyroid to 14.36+/-0.44 in hyperthyroid, and decreased in hypothyroid mitochondria to 8.62+/-0.63 nmol Ca(2+)/mg/s. Furthermore, the K(i) for the specific inhibitor Ru(360), depends on the thyroid status, i.e. 18, 19 and 13 nM for control, hyper- and hypothyroid mitochondria, respectively. In addition, the binding of 103Ru(360) was increased in hyperthyroid and decreased in hypothyroid mitochondria. Scatchard analysis for the binding of 103Ru(360) showed the following values: 28, 40 and 23 pmol/mg for control, hyper- and hypothyroid mitochondria, respectively. The K(d) for 103Ru(360) was found to be 30.39, 37.03 and 35.71 nM for controls, hyper- and hypothyroid groups, respectively. When hypothyroid rats were treated with thyroid hormone, mitochondrial Ca(2+) transport, as well as 103Ru(360) binding, reached similar values to those found for euthyroid mitochondria.