title: Transcellular sodium transport in cultured cystic fibrosis human nasal epithelium.
abstract: Cystic fibrosis (CF) airway epithelia exhibit raised transepithelial Na+ transport rates, as determined by open-circuit isotope fluxes and estimates of the amiloride-sensitive equivalent short-circuit current (Ieq). To study the contribution of apical and basolateral membrane paths to raised Na+ transport in CF, CF nasal epithelial cultures were studied with double-barreled Na(+)-selective microelectrodes and the Ussing chamber technique. Intracellular Na+ activity (acNa) was 24.1 +/- 1.5 mM (n = 36), a value similar to acNa of normal nasal epithelial cells. Reduction of luminal [Na+] to 3 mM abolished Ieq and reduced acNa. Amiloride (10(-4) M) abolished Ieq but increased acNa from 20 +/- 2 to 36 +/- 7 mM (n = 10). Amiloride-induced increase in acNa was not affected by serosal [Na+] reduction but was blocked by preexposure to reduced luminal [Na+]. Amphotericin B increased Ieq during amiloride exposure, indicating that amiloride did not inhibit NA(+)-K(+)-ATPase. Ouabain abolished Ieq and slowly raised acNa. Reduction of serosal [Na+] led to a decrease in acNa that was blocked by bumetanide. It is concluded that 1) CF airway epithelia exhibit an increased apical membrane Na+ permeability, 2) acNa is regulated to a normal level in CF cells despite increased transcellular Na+ fluxes, 3) the abnormal increase in acNa in response to amiloride is dependent on luminal Na+, 4) Na+ is transported across the basolateral membrane by a bumetanide-sensitive cotransport mechanism, and 5) ouabain inhibits the basolateral Na(+)-K(+)-ATPase, causing slow dissipation of the chemical and electrical gradients across the cell membranes.
authors.affiliation: Department of Medicine, School of Medicine, University of North Carolina, Chapel Hill 27514.
authors.forename: N J
authors.initials: NJ
authors.lastname: Willumsen
authors.forename: R C
authors.initials: RC
authors.lastname: Boucher
mesh_terms: D000293:Adolescent; D000328:Adult; D000584:Amiloride / Q000494:pharmacology; D000666:Amphotericin B / Q000494:pharmacology; D001692:Biological Transport; D002034:Bumetanide / Q000494:pharmacology; D002478:Cells, Cultured; D002648:Child; D003550:Cystic Fibrosis / Q000378:metabolism*; D004594:Electrophysiology; D004848:Epithelium; D005260:Female; D006801:Humans; D008297:Male; D009297:Nasal Mucosa / Q000378:metabolism*; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000493:pharmacokinetics* / Q000494:pharmacology
chemical_list: D002034:Bumetanide; D010042:Ouabain; D000584:Amiloride; D000666:Amphotericin B; D012964:Sodium