Fig. 7.
Coordinated thermodynamic and metabolic communication among selected amino acid transport systems in epithelial membranes. Amino acids are shown as cationic (AA+), zwitterion neutral (AAO), anionic (AA–), or generic (AA). Ion exchangers interject their important roles in modulating the secondary active transporters of amino acids. Various mechanisms maintain pH < 7 at the immediate apical membrane surface in various tissues. This figure is a generic representation of an epithelial cell, and not all shown transporters are in every tissue type. The role of ACE2 is described in the main text