Abstract
Efflux of cationic amino acids lysine, arginine and ornithine at the basolateral membrane (BLM) of intestinal and renal tubular epithelia is defective in patients with LPI. Assuming that BLM of epithelial cells and plasma membrane of parenchymal cells are functionally analogous, we studied Na+ - independent transport of cationic amino acids and homoarginine (a nonmefabolized analogue) in cultured LPI fibreblasts and measured L-leucine transport as internal control. Net uptake of cationic amino acids was increased in LPI cells; homoarginine leucine uptake ratio was 0.30 ± 0.07 and 0.26 ± 0.01 (mean ± SEM) (p < 0.05) in LPI and control cells, respectively, at 10 min. The intracellular pool of cationic amino acids was increased (lys/ala 0.47 ± 0.05 vs. 0.31 ± 0.02; p< 0.01). The % trans-stimulation of homoarginine efflux was 1.0 ± 0.5 % in LPI homozygotes, 10 ± 0.5 % in heterozygotes and 22 ± 0.5 % in control cells. Our findings imply that the transport mutation in LPI is expressed asymmetrically at the membrane and concordantly at the basolateral membrane of epithelial and plasma membrane of parenchymaL cells.
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