Exercise inhibits epithelial sodium channels in patients with cystic fibrosis

The aim of this study was to determine the effects of a single exercise bou t on luminal Cl- and Na+ conductance in the respiratory epithelium of patie nts with cystic fibrosis (CF). In nine patients with CF and nine healthy co ntrol subjects, the transepithelial electrical potential difference (PID) o f the nasal respiratory epithelium was recorded, first at rest and then dur ing moderate-intensity exercise. Under both conditions, PD was first measur ed while superfusing the epithelium with isotonic saline. Then, the effects of amilorlde and amiloride plus low chloride plus isoproterenol were deter mined. Exercise resulted in a significant lower PID compared with rest in p atients with CF (-6.6 +/- 16.6 mV versus -33.6 +/- 10.0 mV, p < 0.0001) and control subjects (0.1 +/- 8.7 mV versus -7.1 +/- 5.1 mV, p < 0.01). The ef fects of amilorlde on PID were reduced during exercise compared with rest i n patients with CF (+15.8 +/- 9.5 mV versus + 26.1 +/- 11.0 mV, p < 0.01) a nd control subjects (+5.8 +/- 4.8 mV versus +10.0 +/- 3.1 mV, p < 0.01). Th ere was no effect of exercise on chloride conductance in patients with CF a nd control subjects. We conclude that moderate-intensity exercise partially blocks the amiloride-sensitive sodium conductance in the respiratory epith elium. The inhibition of luminal sodium conductance could increase water co ntent of the mucus in the CF lung during exercise and may, in part, explain the beneficial effects of exercise in patients with CF.