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Schematic location and functioning of the RFC in hepatocytes, small intestine, colon, and epithelial cells of the choroid plexus

Folates from supplementation (eg, folic acid and 5-methyl-THF) are transported intracellularly from the lumen of the proximal small intestine by the reduced folate carrier (RFC; folate transporter 1; SLC19A1 [Solute Carrier Family 19 Member 1]). RFC is also designated as solute carrier family 19 member 1 (SLC19A1). RFC is the main pathway for folate delivery from the serum and extracellular space. In the diagram, an apical surface of polarized epithelial cells is marked by irregular contour.

Abbreviations: 5-methyl-THF = 5-methyl-tetrahydrofolate. (Source: Shulpekova Y, Nechaev V, Kardasheva S, et al. The concept of folic acid in health and disease. Molecules 2021;26(12):3731.) (Modified by Dr. Douglas Lanska. Creative Commons Attribution 4.0 [CC BY] license.)