Active sodium transport by turtle colon via an electrogenic Na-K exchange pump

Kevin L. Kirk, Dan R. Halm, David C. Dawson

Research output: Contribution to journalArticle

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Abstract

Active sodium absorption by a variety of epithelia is abolished by ouabain, but the obligatory coupling between the movement of sodium and potassium expected from a basolateral (Na+ + K+) ATPase has not been convincingly demonstrated1. According to the model of Koefoed-Johnsen and Ussing2, the asymmetric cation selectivities of the apical and basolateral membranes prevent basolateral Na-K exchange from being expressed as opposing transmural ion flows. An additional consequence of this asymmetry is that the short-circuit current (ISC) cannot be identified with the current through the sodium-potassium pump. We used the polyene antibiotic, amphotericin-B, to reduce the resistance and the cation selectivity of the apical membrane of isolated turtle colon so that the basolateral membrane current could be dissected into two components: one through a barium-sensitive potassium channel and another which represents the current associated with ouabain-sensitive, electrogenic, Na-K exchange. Comparison of cation fluxes and short circuit current indicates that in these conditions active sodium absorption is entirely attributable to an electrogenic Na-K pump with a stoichiometry of approximately 3Na:2K.

Original languageEnglish (US)
Pages (from-to)237-239
Number of pages3
JournalNature
Volume287
Issue number5779
DOIs
StatePublished - Dec 1 1980

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