Mediates the Na(+)-independent uptake of organic anions (PubMed:29248594). Transports the conjugated steroids 17-beta- glucuronosyl estradiol (17beta-estradiol 17-O-(beta-D-glucuronate) or E2G) and dehydroepiandrosterone 3-sulfate (DHEAS) at the smooth endoplasmic reticulum membrane (SER), granting access to metabolizing enzymes (PubMed:29248594, PubMed:31127008, PubMed:32818652). Contributes to the metabolism of bile acids such as taurocholate (cholyltaurine) and lithocholate, by functioning as a doorway between SER and cytosol, thereby decreasing their circulating levels and protecting the organism from their detergent properties (PubMed:31509437). Regulates access or exit of drugs to the SER lumen (PubMed:31127008). {ECO:0000269|PubMed:29248594, ECO:0000269|PubMed:31127008, ECO:0000269|PubMed:31509437, ECO:0000269|PubMed:32818652}. This is the function of Ensembl gene identifier ENSG00000257046 (SLCO1B3-SLCO1B7, SLCO1B3-SLCO1B7 readthrough).