Amino acid transport in blood cells. I. Effect of cations on amino acid transport in human leukocytes

The active transport of amino acids by human lymphocytes and granulocytes in vitro was studied with respect to inorganic cationic requirements. Active transport was assumed if intracellular/extracellular amino acid concentration ratios were greater than 1. Sodium was required for the active transport of the nonutilizable amino acid α-aminoisobutyric acid and the utilizable amino acids glycine, proline, alanine, and glutamic acid. Maximal rates of amino acid transport required the presence of optimal concentrations of both sodium and potassium. The transport of these amino acids was inhibited by strophanthin K and stimulated by calcium. In contrast, the active transport of the nonutilizable amino acid aminocyclopentanecarboxylic acid and the utilizable amino acids arginine, lysine, histidine, and methionine was not sodium dependent, not inhibited by strophanthin, nor stimulated by calcium. Independent measurement of net influx and net efflux rates indicated that the effects of sodium and calcium on the steady state intracellular-extracellular concentration gradient reflected stimulation of influx, efflux being unaffected.