Maturation of membrane function: transport of amino acid by rat erythroid cells.
The membrane changes which occur during cellular maturation of erythroid cells have been investigated. The transport of alpha-aminoisobutyric acid, alanine, and N-methylated-alpha-aminoisobutyric acid have been studied in the erythroblastic leukemic cell, the reticulocyte, and the erythrocyte of the Long-Evans rat. The dependence of amino acid transport on extracellular sodium concentration was investigated. Erythrocytes were found to transport these amino acids only by Na-independent systems. The steady state distribution ratio was less than 1. Reticulocytes were found to transport alpha-aminoisobutyric acid and alanine by Na-dependent systems, but only small amounts of N-methylated-alpha-aminoisobutyric acid. Small amounts of these amino acids were transported by Na-independent systems. The steady state distribution ratio was greater than one for Na-dependent transport. The erythroblastic leukemia cell, a model immature erythroid cell, showed marked Na-dependence (greater than 90%) for alpha-aminoisobutyric acid and alanine transport, and greater than 80% for the Na-dependent transport of N-methyl-alpha-aminoisobutyric acid. The steady state distribution ratio for the Na-dependent transport was greater than 4. In the erythroblastic leukemic cell, at least three Na-dependent systems are present: one includes alanine and alpha-aminoisobutyric acid, but excludes N-methyl-alpha-aminoisobutyric acid; one is for alpha-aminoisobutyric acid, alanine and also N-methyl-alpha-aminoisobutyric acid; and one is for N-methyl-alpha-aminoisobutyric acid alone. In the reticulocyte, the number of Na-dependent systems are reduced to two: one for alpha-aminoisobutyric acid and alanine; one for N-methyl-alpha-aminoisobutyric acid. In the erythrocytes, no Na-dependent transport was found. Therefore, maturation of the blast cell to the mature erythrocyte is characterized by a systematic loss in the specificity and number of transport system for amino acids.
D000409:Alanine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000596:Amino Acids / Q000378:metabolism*; D000621:Aminoisobutyric Acids / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D004900:Erythroblasts / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism*; D051381:Rats; D012156:Reticulocytes / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D000621:Aminoisobutyric Acids; D012964:Sodium; D000409:Alanine