Enables carnitine transmembrane transporter activity. Acts upstream of or within carnitine metabolic process; carnitine transport; and triglyceride metabolic process. Located in mitochondrion. Is expressed in several structures, including integumental system; liver; musculoskeletal system; nervous system; and nose. Human ortholog(s) of this gene implicated in rheumatoid arthritis. Orthologous to human SLC22A4 (solute carrier family 22 member 4). [provided by Alliance of Genome Resources, Apr 2022]