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This Article Full Text Full Text (PDF) All Versions of this Article: 289/1/F117    most recent 00471.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (10) Citing Articles via Google Scholar Google Scholar Articles by Gray, D. A. Articles by Palmer, L. G. Search for Related Content PubMed PubMed Citation Articles by Gray, D. A. Articles by Palmer, L. G.

Quantification of K⁺ secretion through apical low-conductance K channels in the CCD

Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, New York

Submitted 29 December 2004 ; accepted in final form 16 February 2005

Outward and inward currents through single small-conductance K⁺ (SK) channels were measured in cell-attached patches of the apical membrane of principal cells of the rat cortical collecting duct (CCD). Currents showed mild inward rectification with high [K⁺] in the pipette (K_p⁺), which decreased as K_p⁺ was lowered. Inward conductances had a hyperbolic dependence on K_p⁺ with half-maximal conductance at 20 mM. Outward conductances, measured near the reversal potential, also increased with K_p⁺ from 15 pS (K_p⁺ = 0) to 50 pS (K_p⁺ = 134 mM). SK channel density was measured as the number of conducting channels per patch in cell-attached patches. As reported previously, channel density increased when animals were on a high-K diet for 7 days. Addition of 8-cpt-cAMP to the bath at least 5 min before making a seal increased SK channel density to an even greater extent, although this increase was not additive with the effect of a high-K diet. In contrast, increases in Na channel activity, assessed as the whole cell amiloride-sensitive current, due to K loading and 8-cpt-cAMP treatment were additive. Single-channel conductances and channel densities were used as inputs to a simple mathematical model of the CCD to predict rates of transepithelial Na⁺ and K⁺ transport as a function of apical Na⁺ permeability and K⁺ conductance, basolateral pump rates and K⁺ conductance, and the paracellular conductance. With measured values for these parameters, the model predicted transport rates that were in good agreement with values measured in isolated, perfused tubules. The number and properties of SK channels account for K⁺ transport by the CCD under all physiological conditions tested.

ROMK; epithelial sodium channels; high-potassium diet; aldosterone; cAMP; epithelial transport model

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