Biophysical and molecular properties of amilorideinhibitable Na+ channels in alveolar epithelial cells

Academic Article

Abstract

  • -The recent immunopurification and cloning of various lung Na+ channel proteins has provided the necessary tools to study Na+ transport at a fundamental level across a number of epithelial tissues. Various macroscopic measurements of Na+ transport have shown that Na+ ions enter the cytoplasm of alveolar cells mainly through amilorideinhibitable Na+ channels. Molecular biology studies have shown the existence of three Na+ channel subunit mRNAs (α, β, and γ-rENaC) in mature fetal (FDLE) and adult alveolar type II (ATII) cells. Patch-clamp studies have demonstrated the existence of various types of amilorideinhibitable Na+ channels, located in the apical membranes of FDLE and ATII cells. β-Agonists and agents that enhance intracellular adenosine 3′,5′-cyclic monophosphate levels increase the open probability of these channels, leading to increased Na+ transport across the alveolar epithelium in vivo. Immunopurification of a putative channel protein from adult ATII cells showed that it contains an amiloride-binding subunit with a molecular mass of 150 kDa. When this protein was reconstituted in planar lipid bilayers, it exhibited single channels with a conductance of 25 pS, which were moderately selective for Na? over K+. The open probability of these channels was increased by the addition of protein kinase A (PKA) and ATP, and was decreased to the same extent by addition of [N-ethyl-N-isopropyl]-2′-4′-amiloride (EIPA) and amiloride (1 μM each) in the apical side of the bilayer, in agreement with the results of patch-clamp studies in ATII cells. Exposure of rats to sublethal hyperoxia increased α-rENaC mRNAandthe functional expression of Na+ channels in alveolar epithelial cells and limited alveolar edema. These findings indicate that alveolar epithelial channels contain at least one family of amiloride-sensitive Na+ channel proteins, which displays a number of unique properties, including sensitivity to EIPA. alveolar type II cells; fetal alveolar cells; patch clamp; short-circuit current;. Copyright ©1996 the American Physiological Society.
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  • Matalon S; Benos DJ; Jackson RM
  • Volume

  • 271
  • Issue

  • 1 PART 1