Antiporter that mediates the import of reduced folates (PubMed:8276792, PubMed:8664315, PubMed:9111015, PubMed:9748272). 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 (PubMed:8276792, PubMed:9111015). Also able to mediate the import of antifolate drug methotrexate (PubMed:8276792, PubMed:8664315, PubMed:9748272). 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) Belongs to the reduced folate carrier (RFC) transporter (TC 2.A.48) family. In contrast to human, not able to transport immunoreactive cyclic dinucleotides, such as cyclic GMP-AMP (2'-3'-cGAMP), an immune messenger produced in response to DNA virus in the cytosol.