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) (PubMed:16887882, PubMed:18337592, PubMed:20628049, PubMed:23550058, PubMed:26426690, PubMed:27805744, PubMed:31436139). Acts as an important mediator of thyroid hormone transport, especially T3, through the blood-brain barrier (Probable) (PubMed:28526555).
