Specific thyroid hormone transmembrane transporter, that mediates both uptake and efflux of thyroid hormones across the cell membrane independently of pH or a Na(+) gradient. Major substrates are the iodothyronines T3 and T4 and to a lesser extent rT3 and 3,3-diiodothyronine (3,3'-T2) (   ). Acts as an important mediator of thyroid hormone transport, especially T3, through the blood-brain barrier (Probable) .
Subcellular locations: Cell membrane, Apical cell membrane
Highly expressed in liver and heart . In adult brain tissue expression is largely confined to endothelial cells of the blood-brain barrier (at protein level) (, ).