Sodium-ion dependent, low affinity carnitine transporter. Probably transports one sodium ion with one molecule of carnitine. Also transports organic cations such as tetraethylammonium (TEA) without the involvement of sodium. Relative uptake activity ratio of carnitine to TEA is 1.78. A key substrate of this transporter seems to be ergothioneine (ET).
Widely expressed. Highly expressed in whole blood, bone marrow, trachea and fetal liver. Weakly expressed in kidney, skeletal muscle, prostate, lung, pancreas, placenta, heart, uterus, spleen and spinal cord. Highly expressed in intestinal cell types affected by Crohn disease, including epithelial cells. Expressed in CD68 macrophage and CD43 T-cells but not in CD20 B-cells. Predominantly expressed in CD14 cells in peripheral blood mononuclear cells.
Involvement in disease
Genetic variations in SLC22A4 are a cause of susceptibility to rheumatoid arthritis (RA) [MIM:180300]. It is a systemic inflammatory disease with autoimmune features and a complex genetic component. It primarily affects the joints and is characterized by inflammatory changes in the synovial membranes and articular structures, widespread fibrinoid degeneration of the collagen fibers in mesenchymal tissues, and by atrophy and rarefaction of bony structures.
Belongs to the major facilitator superfamily. Organic cation transporter family.