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BioMed Research International
Volume 2013 (2013), Article ID 698674, 8 pages
http://dx.doi.org/10.1155/2013/698674
Research Article

Is the Second Sodium Pump Electrogenic?

Laboratorio de Fisiología Molecular, Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas (IVIC), Apartado 20632, Caracas 1020 Districo Capital, Venezuela

Received 11 August 2012; Revised 11 November 2012; Accepted 22 November 2012

Academic Editor: Michael D. Coleman

Copyright © 2013 L. E. Thomas et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Transepithelial sodium transport is a process that involves active Na+ transport at the basolateral membrane of the epithelial cell. This process is mediated by the Na+/K+ pump, which exchanges 3 internal Na+ by 2 external K+ inducing a net charge movement and the second Na+ pump, which transports Na+ accompanied by Cl and water. It has been suggested that this pump could also be electrogenic. Herein, we evaluated, in MDCK cells, the short-circuit current ( ) generated by these Na+ pumps at the basolateral membrane of the epithelial cells, using amphotericin B as an apical permeabilizing agent. In Cl-containing media, induced by amphotericin B is totally inhibited by ouabain, indicating that only the electrogenic Na+/K+ pump is detectable in the presence of Cl. Electrogenicity of the second Na+ pump can be demonstrated in Cl-free media. The existence of a furosemide-sensitive component of , in addition to an ouabain-sensitive one, was identified in absence of chloride. Passive Cl movement associated with the function of the second Na+ pump seems to be regulated by the pump itself. These results demonstrate that the second Na+ pump is an electroneutral mechanism result from the stoichiometric movement of Na+ and Cl across the basolateral plasma membrane of the epithelial cell.