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Effects of cystic fibrosis serum on calcium influx and secretion using isolated tracheal epithelial cells

Hamster trachea epithelial (HTE) cells were shown to respond to 20% Cystic fibrosis serum (CFS) by secreting twice as much protein as in the presence of 20% normal human serum (NHS). Seum from obligate heterozygotes (HHS) produced an intermediate effect. A peak of Ca2+ entry into the HTE cells occurred about 30 min after exposure to 20% CFS, followed by a slow decline to basal levels. In contrast, 20% NHS did not cause an influx of Ca2+ and HHS produced an influx to about half that of CFS. Increasing concetrations (5‐30%) of pooled NHS had no effect on HTE cell Ca2+ uptake or secretion, but pooled CFS and HHS caused progressive increases in Ca2+ influx and protein secretion from 10 to 25% sera. The CFS‐induced Ca2+ influx and secretion were about twice those of HHS throughout the range of serum concentrations tested, suggesting the presence of a modulatory influence in HHS. When EGTA was used to chelate extracellular Ca2+ in the presence of CFS, Ca2+ influx was prevented and there was no stimulation of secretion. lonophore A23187 allowed Ca2+ entry into HTE cells in the presence or absence ofserum and a heightened level of secretory activity followed. The time course of Ca2+ influx under the influence of CFS was shown to correspond to the efflux of Na+ from the cells. Also verapamil, a Ca2+ channel blocking agent, inhibited CFS‐induced Ca2+ influx by 50% at 10−5M and prevented secretion. Thus, it appears that CFS, but not NHS, contains an agent which stimulates Ca2+ uptake into HTE cells by means of a Ca2+ channel and/or Na+‐Ca2+ exchange mechanism, and that increased intracellular Ca2+ levels then trigger secretion. The intermediate HTE cellr esponse to HHS suggests that half of the CFS stimulatory agent is present as would be expected in a gene dose effect, lending support for a agentic basis for CF.