Mediates the Na(+)-independent high affinity transport of organic anions such as the thyroid hormones thyroxine (T4) and rT3. Other potential substrates, such as triiodothyronine (T3), estradiol-17-beta-glucuronide, estrone-3-sulfate and sulfobromophthalein (BSP) are transported with much lower efficiency (By similarity). May play a significant role in regulating T4 flux into and out of the brain (By similarity). Highly expressed in cerebral microvessels (at protein level). Highly expressed in cerebral microvessels throughout the brain and in tanycytes of the third ventricle. Belongs to the organo anion transporter (TC 2.A.60) family.