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 Ca 2+ 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 Ca 2+ and HHS produced an influx to about half that of CFS. Increasing concetrations (5‐30%) of pooled NHS had no effect on HTE cell Ca 2+ uptake or secretion, but pooled CFS and HHS caused progressive increases in Ca 2+ influx and protein secretion from 10 to 25% sera. The CFS‐induced Ca 2+ 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 Ca 2+ in the presence of CFS, Ca 2+ influx was prevented and there was no stimulation of secretion. lonophore A23187 allowed Ca 2+ entry into HTE cells in the presence or absence ofserum and a heightened level of secretory activity followed. The time course of Ca 2+ influx under the influence of CFS was shown to correspond to the efflux of Na + from the cells. Also verapamil, a Ca 2+ channel blocking agent, inhibited CFS‐induced Ca 2+ influx by 50% at 10 −5 M and prevented secretion. Thus, it appears that CFS, but not NHS, contains an agent which stimulates Ca 2+ uptake into HTE cells by means of a Ca 2+ channel and/or Na + ‐Ca 2+ exchange mechanism, and that increased intracellular Ca 2+ 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.