Abstract 18573: Genetic Variation of the Alpha-Subunit of the Epithelial Sodium Channel Influences the Lung Fluid Response to Hypoxia in Healthy Humans

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Cardiogenic pulmonary edema is a life-threatening complication in patients with heart failure (HF) resulting from increased alveolar Cl- secretion and inhibition of alveolar epithelial Na+ channels (ENaC). Not all HF patients develop pulmonary edema, despite similar clinical characteristics, suggesting a genetic component to edema formation in response to cardiac failure. The ENaC are crucial for alveolar fluid clearance, with the alpha subunit demonstrating particular importance. We have previously found that genetic variation of the alpha subunit (SCNN1A) of ENaC, an alanine (A) to threonine (T) substitution, influences ion regulation during exercise and in response to albuterol. In the present study, we sought to determine the influence of the threonine variant (T663; AT/TT group) on lung fluid regulation in response to normobaric hypoxia, an environmental condition known to increase pulmonary capillary hydrostatic stress in healthy humans. Lung ion and fluid changes were assessed using exhaled Na+ (ENa+) and the lung diffusing capacity for carbon monoxide and nitric oxide (DLCO and DLNO, respectively) to determine alveolar-capillary membrane conductance (DM). 19 healthy subjects (n=8 vs. 11, %female=50 vs. 62%, age=27±1 vs. 28±2yrs., ht=171±3 vs. 173±2cm, wt=69±6 vs.72±3kg , BMI=23±1 vs.24±1kg/m2 , for AA and AT/TT, respectively) completed two overnight visits in a hypoxic tent simulating just over 5,400m. The visits were randomized to inhaled placebo (P) or inhaled amiloride (Aml, 1.5mg in 5ml normal saline, used to inhibit ENaC activity) with ENa+, DLCO, and DM assessed at baseline and following 12 hours of hypoxic exposure. There was an effect of genotype on the ENa+ response to hypoxia with placebo that was abolished with amiloride, but no effect of genotype on the diffusing capacity of the lung (Table). These results suggest that genetic variation of SCNN1A may influence ion regulation in the lung under conditions of elevated hydrostatic stress.