Proton-coupled transport of organic solutes in animal cell membranes and its relation to Na+ transport

Abstract

Recent studies on proton-coupled transport of organic solutes in animal cell membranes were reviewed. In the intestinal and renal brush border membranes, transport of intact small peptides (di- or tri-peptides) has been established to be cotransported with H+. The peptide transport is Na+-independent, dependent on a pH gradient, electrogenic as revealed by transport-associated membrane depolarization and conductance increase, and reveals a marked overshoot uptake when a sufficiently large proton gradient is imposed across the membrane. Similar properties are found for L-lysine transport by the brush border membrane vesicles from mullet kidney and for L-leucine transport in some cultured cells. Partial involvement of H+ in Na+-dependent transport has also been reported for some organic acids, L-glutamate, and citrate. The physiological meanings of these purely H+-dependent and partially H+-dependent transports have been discussed based on available data.