Ionic requirements for amino acid transport in the rat kidney cortex slice: I. Influence of extracellular ions

Abstract 1. 1. Active transport of amino acids in rat kidney cortex slices diminished as the Na + concentration of the medium was decreased below physiologic levels. In Na + -free media, active transport of glycine and α-amino [ i - 14 C]isobutyric acid was abolished, but active transport of lysine persisted. 2. 2. Lysine transport was found to be mediated by two mechanisms—one Na + dependent and ouabain sensitive, and the other independent of Na + and insensitive to ouabain. 3. 3. Maximal transport of amino acids occurred over a narrow range of medium K + concentrations, falling off at higher and lower K + levels. 4. 4. Substitution of other ions for Na + in the medium caused significant alterations of the intracellular and extracellular fluid spaces of the tissues. 5. 5. Replacement of medium Na + by K + resulted in tissue swelling and suppression of amino acid transport beyond that caused by the absence of Na + . 6. 6. The common ionic requirements of kidney ATPase systems and of the mechanisms for active transport of certain amino acids suggest that these processes may be intimately related.