Chronic regulation of transepithelial Na+ transport by the rate of apical Na+ entry

• Published in: The American journal of physiology Vol. 270; no. 2 Pt 1; p. C600
• Main Authors: Rokaw, M D, Sarac, E, Lechman, E, West, M, Angeski, J, Johnson, J P, Zeidel, M L
• Format: Journal Article
• Language: English
• Published: United States 01.02.1996
• Subjects: Amiloride - pharmacology; Animals; Biological Transport - drug effects; Cell Line, Transformed; Cell Membrane - metabolism; Epithelium - metabolism; Intracellular Membranes - metabolism; Kidney - cytology; Kidney - metabolism; Quaternary Ammonium Compounds - pharmacology; Sodium - antagonists & inhibitors; Sodium - metabolism; Sodium Channels - metabolism; Sodium-Potassium-Exchanging ATPase - metabolism; Time Factors; Xenopus laevis
• ISSN: 0002-9513
• DOI: 10.1152/ajpcell.1996.270.2.C600

In several settings in vivo, prolonged inhibition of apical Na+ entry reduces and prolonged stimulation of apical entry enhances the ability of renal epithelial cells to reabsorb Na+, an important feature of the load-dependent regulation of renal tubular Na+ transport. To model this load dependency, apical Na+ entry was inhibited or stimulated for 18 h in A6 cells and vectorial transport was measured as short-circuit current (Isc) across monolayers on filter-bottom structures. Basal amiloride-sensitive Isc represents the activity of apical Na+ channels, whereas Isc after permeabilization of the apical membrane to cations with nystatin represents maximal activity of the basolateral Na(+)-K(+)-ATPase. Chronic inhibition of apical Na+ entry by 18-h apical exposure to amiloride or replacement of apical Na+ with tetramethylammonium (TMA+), followed by washing and restoration of normal apical medium, revealed a persistent decrease in Isc that remained despite exposure to nystatin. Both basal and nystatin-stimulated Isc recovered progressively after restoration of normal apical medium. In contrast, chronic stimulation of apical Na+ entry by short circuiting the epithelium increased Isc in the absence and presence of nystatin, indicating upregulation of both apical Na+ channels and basolateral Na(+)-K(+)-ATPase. Basolateral equilibrium [3H]ouabain binding was reduced to 67 +/- 5% in TMA+ vs. control cells, whereas values in 18-h short-circuited cells increased by 42 +/- 19%. The results demonstrate that load dependency of tubular Na+ transport can be modeled in vitro and indicate that the regulation of Na(+)-K(+)-ATPase observed in these studies occurs in part by changes in the density of functional transporter proteins within the basolateral membrane.