Antiporter that mediates the import of reduced folates (PubMed:11600421, PubMed:19243012). Mechanistically, acts as a secondary active transporter, which exports intracellular organic anions down their concentration gradients to facilitate the uptake of its substrates (By similarity). Has high affinity for N5-methyltetrahydrofolate, the predominant circulating form of folate (By similarity). Also able to mediate the import of antifolate drug methotrexate (PubMed:10827155, PubMed:11600421). 5-amino-4-imidazolecarboxamide riboside (AICAR), when phosphorylated to AICAR monophosphate, can serve as an organic anion for antiporter activity (By similarity). (6S)-5-methyl-5,6,7,8-tetrahydrofolate(out) + 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide(in) = (6S)-5-methyl-5,6,7,8-tetrahydrofolate(in) + 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide(out) Expressed in liver, heart, brain, spleen, lung and skeletal muscle. Belongs to the reduced folate carrier (RFC) transporter (TC 2.A.48) family.