Cystic fibrosis and phosphatidylcholine biosynthesis.

The cystic fibrosis (CF) gene defect may be associated with a defect in membrane recycling. We have investigated the metabolism of the main constituent of plasma membrane, phosphatidylcholine (PC). In this study of platelets and fibroblasts, we show an increased uptake of choline into PC of CF cells as compared with normal cells. No accumulation of PC was seen. Other patients with respiratory disease (not CF) showed normal rates of incorporation of choline into platelet PC. Platelets from heterozygote individuals showed intermediate turnover rates of choline incorporation into PC. The increase in choline incorporation into PC in CF platelets was not due to modified or increased sensitivity to either cAMP or prostaglandin E2. The total amount and the proportions of the major phospholipids in platelets of control and CF individuals were identical. These findings indicate an increased turnover rate of this phospholipid in CF cells rather than an increased net synthesis.

Hormone-stimulated cyclic AMP production by skin fibroblasts cultured from healthy persons and patients with cystic fibrosis.

The experiments reported here illustrate a few of the factors apart from genes which can influence hormone-responsive generation of cyclic adenosine 3':5'-monophosphate in human fibroblasts. For both normal and cystic fibrosis fibroblasts, the isoproterenol stimulation ratio was maximal 2 to 3 days after subculture and declined thereafter; prostaglandin E1 stimulation ratio was maximal 7 to 10 days after subculture. Cells dislodged from the plate by either scraping or typsinization had reduced isoproterenol or prostaglandin E1 stimulation ratios compared to cells studied in situ. Fibroblasts from healthy controls and cystic fibrosis patients plated simultaneously and grown in three different culture conditions responded similarly to the change in growth conditions. Addition to the incubation medium of polyamines, calcium, magnesium, or guanosine triphosphate did not alter the stimulation ratios for isoproterenol or prostglandin E1. Repeated measures analysis indicates that cellular content of cyclic adenosine 3':5'-monophosphate is not a reliable measure for comparing cell lines; isoproterenol stimulation ratio is a reliable measure, but there is large variation from cell line to cell line. Isoproterenol stimulation ratio was the same for normal and cystic fibrosis fibroblasts in each of the three culture conditions tested at both three and ten days after subculture.

Growth characteristics and protein content of tissue-cultured fibroblasts from cystic fibrosis patients.

Proliferation rates and cellular protein content have been measured in cultured fibroblasts derived from the skin of normal volunteers and cystic fibrosis patients. Three methods of measuring growth indicated that under our conditions, CF fibroblasts divide normally with a mean doubling time of 29 hr. During the logarithmic growth phase, however, lower cell protein/DNA ratios were observed consistently in CF cultures. This difference was not present in contact-inhibited, confluent fibroblasts. The finding of an apparent reduction in protein synthesis during rapid division, coupled with an observation by others that CF fibroblasts fail to normally induce collagen formation, suggests the possibility of a disturbance in the biochemical regulation of protein synthesis.