Deposition, clearance, and effects of aerosolized amiloride in sheep airways

Persistent Na+ absorption across a relatively Cl- impermeable epithelial barrier may contribute to the smaller water content of airway surface liquid (ASL) in cystic fibrosis. In this study, the feasibility and effectiveness of delivering an inhibitor of Na+ absorption, amiloride, by aerosol to the ASL of awake sheep was evaluated. Aerosolization of 6 X 10(-3) M amiloride, with [14C]amiloride, resulted in an estimated concentration of 7 X 10(-4) M in ASL. The transtracheal electric potential difference (PD), an index of the rate of Na+ absorption, was significantly inhibited (-29%) immediately after aerosolization of amiloride. The inhibition was short-lived and was correlated with rapid disappearance of the drug from ASL (half-time, 10.5 min between 0 and 30 min after aerosolization). Amiloride but not aerosol vehicle increased ASL volume significantly. The unidirectional flow of [14C]amiloride from the lumen to the submucosa across excised, short-circuited sheep airways exceeded flow from submucosa to lumen by a factor of at least 6. This finding suggests that amiloride is actively absorbed and is consistent with the rapid clearance from the airway surface and the short-lived effects of aerosolized amiloride in vivo. We conclude that sufficient concentrations of amiloride can be delivered to sheep airways by aerosol to inhibit PD and Na+ absorption for short periods.