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This Article Full Text Full Text (PDF) All Versions of this Article: 297/2/F389    most recent 90528.2008v1 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 PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Google Scholar Articles by Frindt, G. Articles by Palmer, L. G. PubMed PubMed Citation Articles by Frindt, G. Articles by Palmer, L. G.

K⁺ secretion in the rat kidney: Na⁺ channel-dependent and -independent mechanisms

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

Submitted 4 September 2008 ; accepted in final form 21 May 2009

Renal Na⁺ and K⁺ excretion was measured in rats with varying dietary K⁺ intake. The requirement for channel-mediated distal nephron Na⁺ reabsorption was assessed by infusing the animals with the K⁺-sparing diuretic amiloride via osmotic minipumps. At infusion rates of 2 nmol/min, the concentration of amiloride in the urine was 38 µM, corresponding to concentrations of 9–23 µM in the distal tubular fluid, sufficient to block >98% of Na⁺ transport through apical Na⁺ channels (ENaC). With a control K⁺ intake (0.6% KCl), amiloride reduced K⁺ excretion rates (U_KV) from 0.85 ± 0.15 to 0.05 ± 0.01 µmol/min during the first 2 h of infusion, suggesting that distal nephron K⁺ secretion was completely dependent on the activity of Na⁺ channels. When K⁺ intake was increased by feeding overnight with a diet containing 10% KCl, amiloride reduced U_KV from 7.5 ± 0.7 to 1.3 ± 0.1 µmol/min despite an increased plasma K⁺ of 9 mM, again suggesting a major but not exclusive role for the Na⁺ channel-dependent pathway of K⁺ secretion. The maximal measured rates of amiloride-sensitive K⁺ excretion correspond well with estimates based on apical K⁺ channel activity in distal nephron segments. However, when the animals were adapted to the high-K⁺ diet for 7–9 days, the diuretic decreased U_KV less, from 6.1 ± 0.6 to 3.0 ± 0.8 µmol/min, indicating an increasing fraction of K⁺ excretion that was independent of Na⁺ channels. This indicates the upregulation of a Na⁺ channel-independent mechanism for secreting K⁺.

amiloride; K⁺ adaptation; K⁺ channels

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				G. Frindt and L. G. Palmer Surface expression of sodium channels and transporters in rat kidney: effects of dietary sodium Am J Physiol Renal Physiol, November 1, 2009; 297(5): F1249 - F1255. [Abstract] [Full Text] [PDF]