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Am J Physiol Cell Physiol 261: C332-C341, 1991;
0363-6143/91 $5.00
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AJP - Cell Physiology, Vol 261, Issue 2 C332-C341, Copyright © 1991 by American Physiological Society

ARTICLES

Transcellular sodium transport in cultured cystic fibrosis human nasal epithelium

N. J. Willumsen and R. C. Boucher
Department of Medicine, School of Medicine, University of North Carolina, Chapel Hill 27514.

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.


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