Abstract

In lysinuric protein intolerance (LPI), impaired transport of cationic amino acids in kidney and intestine is due to mutations of the SLC7A7 gene. To assess the functional consequences of the LPI defect in nonepithelial cells, we have characterized cationic amino acid (CAA) transport in human fibroblasts obtained from LPI patients and a normal subject. In both cell types the bidirectional fluxes of arginine are due to the additive contributions of two Na(+)-independent, transstimulated transport systems. One of these mechanisms, inhibited by N-ethylmaleimide (NEM) and sensitive to the membrane potential, is identifiable with system y(+). The NEM- and potential-insensitive component, suppressed by L-leucine only in the presence of Na(+), is mostly due to the activity of system y(+)L. The inward and outward activities of the two systems are comparable in control and LPI fibroblasts. Both cell types express SLC7A1 (CAT1) and SLC7A2 (CAT2B and CAT2A) as well as SLC7A6 (y+LAT2) and SLC7A7 (y+LAT1). We conclude that LPI fibroblasts exhibit normal CAA transport through system y(+)L, probably referable to the activity of SLC7A6/y+LAT2.