Active <SUP>22</SUP>Na<SUP>+</SUP> 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.

The role of α-, β-, and γ-ENaC subunits in distal lung epithelial fluid absorption induced by pulmonary edema fluid

“…One of these Na ϩ channels is the amiloridesensitive epithelial Na ϩ channel (ENaC) that is composed of ␣-, ␤-, and ␥-subunits (6). However, it has been shown that normal mammalian lung epithelia have both an amiloridesensitive and an amiloride-insensitive component to their active Na ϩ transport both in vivo (24) and in vitro (8,25). Presently, the molecular basis of this amiloride-insensitive Na ϩ transport is poorly understood.…”

Amiloride-insensitive Na+and fluid absorption in the mammalian distal lung

“…Dichlorobenzamil does not block epinephrine-induced fluid absorption in fetal lambs, but it attenuates fluid absorption in 6-wk-old lambs and totally blocks absorption in 6-mo-old lambs (40,41). The amount of amilorideinsensitive Na ϩ transport stabilizes after birth in the guinea pig as there are similar amounts of amiloride-insensitive apical to basolateral movement of 22 Na across the lung epithelia of 7-and 30-day-old animals (66).…”

Effects of cardiogenic edema fluid on ion and fluid transport in the adult lung

“…Normal mammalian lung epithelia have been shown to have both an amiloride-sensitive and an amiloride-insensitive component to their active Na ϩ transport both in vivo (e.g., Ref. 28) and in vitro (10,17,29). In vivo, this amiloride-insensitive component may represent up to 50% of the total AFC (23).…”