Trans-membrane fluxes of leucine were measured in mouse C127i cells transfected with the wild type (C127 CFTRw/t) or the delta F508 CF gene (C127 CFTR delta F508). Leucine efflux was significantly faster in C127 CFTRw/t cells. On the contrary, leucine influx was comparable in the two cell lines and referable to a "L-type" transport system. No significant differences in leucine content were detected among the two cell lines when maintained in complete growth medium; in contrast, after prolonged incubation in amino-acid-free saline solution, the amount of intracellular leucine was significantly smaller in C127 CFTRw/t than in C127 CFTR delta F508 cells. Leucine behavior was shared by other neutral amino acids with non polar side chains. These results suggest that the expression of normal CFTR increases the efflux of a subgroup of neutral amino acids.
