Thyroid hormone effect on gene expression of the adenine nucleotide translocase in different rat tissues

The ADP/ATP transport across the mitochondrial membrane is achieved by the adenine nucleotide translocase (ANT), an integral inner mitochondrial membrane protein. As deduced from experiments in rat liver in vivo and in isolated rat liver mitochondria this ADP/ATP transport is accelerated by thyroid hormone application, thus explaining, at least to a considerable extent, the thyroid hormone mediated increase in mitochondrial metabolic activity. The present study investigates the effect of T3 on rat liver, heart, and kidney ANT gene expression. As shown by Northern blot analysis, a cDNA for beef heart ANT-mRNA showed cross-hybridization with the ANT-mRNA from rat heart, liver, and kidney. Hypo- and hyperthyroid rats showed no differences in size nor in amounts of heart, liver, and kidney ANT-mRNA. Measurement of heart ANT-protein level revealed no major differences among the various thyroid states. Thus, the long-term action of thyroid hormones on increasing the carrier-mediated ADP/ATP translocation cannot be ascribed to an effect of T3 on ANT gene expression. The mechanism by which T3 activates this transporter system remains to be identified but some possibilities are suggested.