Pleiotropic drug resistance in cystic fibrosis fibroblasts: increased resistance to cyclic AMP

Distinguishing homozygous and heterozygous cystic fibrosis fibroblasts from normal cells by differences in sodium transport

We have found that cultured fibroblasts from patients with cystic fibrosis (CF) accumulate less 22Na in the presence of ouabain than do normal cells. After equilibration with 22Na in ouabain-exposed cells to that in unexposed cells, after five hours of incubation, was 2.34 +/- 0.14 (mean +/- S.D.) in 13 fibroblast strains from normal subjects and 1.33 +/- 0.08 in eight strains from patients with CF. Cells from eight different obligate CF heterozygotes (parents of children with CF) had a ratio of 1.38 +/- 0.07; those from three unaffected siblings (who have a two-thirds chance of carrying the disease) had a ratio of 1.27 +/- 0.04. The differences between CF homozygotes or heterozygotes and normal subjects were highly significant (P < 0.001), but there was considerable overlap between CF homozygotes and heterozygotes. This abnormality of sodium transport provides an unequivocal in vitro test that distinguishes normal cells from cells derived from CF homozygotes or heterozygotes. It should be useful for the identification of carriers of the CF gene.

Killing of fibroblasts by dexamethasone or dibutyryl adenosine 3',5'-monophosphate is not a valid test for cystic fibrosis

Assays based on the counting of total cells and of colony-forming cells were used to demonstrate that neither dexamethasone nor dibutyryl adenosine 3',5'-monophosphate (cyclic AMP) kills human fibroblasts under a variety of conditions. These results contradict those of previous studies showing that dexamethasone and dibutyryl cyclic AMP kill a higher percentage of fibroblasts from normal humans than from individuals with cystic fibrosis.