Neutral amino acids are transported by several systems as indicated in Fig. 19.System L, primarily the heterodimer 4F2hc/Lat1 (Slc3a2 + Slc7a5) which is present in both membranes and functions independently of Na+;
System A, primarily ATA2 (Slc38a2) in the abluminal membrane which because it is a Na+-linked transporter is biased towards transport from ISF into the endothelial cells;
ASC, primarily ASCT2 (Slc1a5), an obligatory exchanger that requires the presence of Na+-but is not driven by the Na+ gradient;
System Na+-LNAA a Na+-linked system whose molecular basis is still unknown;
ATB0,+ (SLC6A14) which allows net fluxes without exchange;
And possibly the y+L transporter [4F2hc (SLC3A2) + either y+LAT2 (SLC7A6) or y+LAT1 (SLC7A7)].