Changes in neutral amino acid efflux and membrane potential associated with the expression of CFTR protein.

The expression of wild type CFTR facilitates the efflux of neutral amino acids (Rotoli et al., Biochem. Biophys. Res. Commun. 204: 653-658, 1994); as a result, after an extensive depletion of intracellular amino acid pool obtained through an incubation in saline solution, the intracellular leucine levels were lower in murine C127 cells transfected with the wild type CF gene (C127 CFTRw/t) than in cells transfected with either mutant CF (C127 CFTRΔF508 cells) or mock vector only. No change in amino acid efflux was detected when C127 CFTRw/t and C127 CFTRw/t and C127 CFTRΔF508 cells were studied under conditions known to activate protein kinase A. Upon an incubation in Cl(-) free medium, a permeant analogue of cAMP caused a marked cell depolarization of C127 CFTRw/t cells but not of C127 CFTRΔF508 cells, thus showing a functional expression of CFTR protein in the former cell line. However, we found that, upon a Cl(-) free incubation and in the absence of exogenous cAMP, C127 CFTRw/t cells developed a marked hyperpolarization that was not detected in C127 CFTRΔF508 cells. It is concluded that the expression of normal CFTR accelerates amino acid efflux and enhances cell hyperpolarization in Cl(-) free media; both these effects appear to be independent from PKA stimulation of CFTR.