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), 17-beta-glucuronosyl estradiol, estrone-3-sulfate and sulfobromophthalein (BSP) are transported with much lower efficiency. May play a significant role in regulating T4 flux into and out of the brain (By similarity). Expressed in both luminal and abluminal membranes of brain capillary endothelial cells. Localized to the apical membrane and basal surfaces of choroid plexus (By similarity). Highly expressed in brain and in Leydig cells in testis. Detected in many brain regions with the exception of pons and cerebellum. Not strongly enriched in cerebral microvessels. Belongs to the organo anion transporter (TC 2.A.60) family.