Cystic fibrosis (CF) is characterised by impaired Cl^– secretion and increased Na⁺ reabsorption in several tissues including respiratory epithelium and results from mutations in the cystic fibrosis conductance regulator protein (CFTR), a cAMP-regulated chloride channel in epithelia. However, only a poor correlation exists between the genotype and lung phenotype, suggesting additional factors influencing the phenotype and course of the disease. There is increasing evidence suggesting that CFTR has multiple functions in addition to its extensively studied role as a chloride channel, linking it to cytoskeleton and energy metabolism. Improved cellular oxygenation has been shown to increase endogenous CFTR maturation and/or trafficking, but the mechanisms are not known (Bebok et al. 2001). We have shown that the phosphorylation of nucleoside diphosphate kinase (NDPK) from the airway apical membrane is stimulated by [Cl^–] but inhibited by [Na⁺] (Muimo et al. 1998). We have also identified NDPK as the first defective kinase in CF using a CF mouse model (Riemen et al. 1998).

Here we compared NDPK-dependent GTP production using γ[³²P]ATP + GDP in HBE submerged monolayers grown at P_O2 3 %, and 21 %. Plasma membranes and cytosol (2.5 µg protein) were prepared and incubated with labelled nucleotides for up to 2 min at 37 °C as previously described (Muimo et al. 1998; Riemen et al. 1998). GTP production was measured by TLC and quantitated by electronic autoradiography. Our results show that tri-nucleotide synthesis increased 7- and 2-fold in cytosol (from 20.6 ± 3.7 to 137 ± 7.8 nmol (mg protein)^-1, means ± S.E.M.) and membrane (from 41.0 ± 2.2 to 72.0 ± 9.4 nmol (mg protein)^-1), respectively, with increased oxygenation. This suggests differential regulation of NDPK from different cellular compartments. It remains to be established whether the improved CFTR and NDPK functions under oxygenation share a similar mechanism.

This work was supported by the CF Trust and Wellcome Trust.