Active ²²Na⁺ transport by the intact lung during early postnatal life

Abstract

The lung relies upon epithelial active transport of Na+ to aid in the clearance of fluid from its air spaces. Because it is unknown whether the rate of active Na+ transport by the distal lung epithelium varies during early postnatal age, we performed studies in young guinea pigs (7 and 30 days after birth). We used a single pass isolated perfused lung model in which a Krebs Ringer bicarbonate solution containing 22Na+, [14C]sucrose, and FITC-dextran was placed into the air spaces of the lungs, and apparent permeability-surface area (PS) products were calculated after determining the changes in lung weight and the concentrations of the isotopes in the vascular effluent. The PS product for 22Na+, but not [14C]sucrose, decreased significantly at both ages when amiloride was infused (final concentration of 10(-4) M). Amiloride also decreased the rate of fluid clearance, as assessed by changes in organ weight, at both ages. Although the absolute rate of amiloride-sensitive 22Na+ transport increased with age, morphometric measurement of the alveolar region demonstrated that the rate of amiloride-sensitive 22Na+ transport per unit alveolar surface area was similar. These data indicate that although the guinea pig lung undergoes significant growth shortly after birth, the rate of amiloride-sensitive active Na+ transport per unit surface area remains constant. Since a component of weight loss was insensitive to amiloride, these in vivo studies suggest that the amiloride-insensitive Na+ transport pathways previously identified in cultured lung epithelium exist in the intact lung.

Pulmonary oedema fluid induces non‐α‐ENaC‐dependent Na+ transport and fluid absorption in the distal lung

“…Our present experiments are consistent with previous studies that show the presence of amiloride‐insensitive Na + transport pathways within the distal regions of the lung. Studies in single pass perfused lungs revealed amiloride‐insensitive 22 Na + and airspace fluid clearance (O'Brodovich et al 1997) and there is amiloride‐insensitive 22 Na + transport in acutely isolated bovine airway (Langridge‐Smith, 1986) and rabbit nasal epithelium (Ropke et al 1996). DLE grown in primary culture have variable amounts of Na + ‐dependent, amiloride‐insensitive I sc (O'Brodovich et al 1990) and human nasal epithelia have amiloride‐insensitive Na + conductive channels (Chinet et al 1993).…”