system A: transport system for alanine and other amino acids, transports MeAIB; system ASC neutral amino acid transporter; system L: large neutral amino acid transport (4F2hc/Lat1 in the rat), transports BCH; system N: Na+-linked transport system for large N rich amino acids, e.g. glutamine, see SNAT; system xc−: cystine, glutamate exchange (mediated by 4F2hc/xCT); system XAG−: possible glutamate transport in luminal membrane; system y+: amino acid transport mediated by CAT1 at blood–brain barrier; system y+L: possible transport of neutral amino acids; ASCT2: Na+-dependent transporter for neutral amino acids (system ASC); ATA2: Na+-linked transporter—alanine preferring (system A); ATBo,+: neutral and basic amino acid transporter; CAT-1: cationic amino acid transporter 1; EAAT1, EAAT3: excitatory amino acid transporters 1 and 3 (abluminal membrane); Na+-LNAA: Na+ linked large neutral amino acid transporter (unknown gene); SNAT3: transporter for N rich amino acids (e.g. glutamine) linked to Na+/H+ exchange; 4F2hc/Lat1: heterodimeric transporter for large neutral amino acids, obligatory exchanger.