ENaC and ROMK activity are inhibited in the DCT2/CNT of TgWnk4 PHAII mice

Am J Physiol Renal Physiol. 2017 Apr 1;312(4):F682-F688. doi: 10.1152/ajprenal.00420.2016. Epub 2016 Nov 9.

Abstract

Mice transgenic for genomic segments harboring PHAII (pseudohypoaldosteronism type II) mutant Wnk4 (with-No-Lysine kinase 4) (TgWnk4PHAII) have hyperkalemia which is currently believed to be the result of high activity of Na-Cl cotransporter (NCC). This leads to decreasing Na+ delivery to the distal nephron segment including late distal convoluted tubule (DCT) and connecting tubule (CNT). Since epithelial Na+ channel (ENaC) and renal outer medullary K+ channel (ROMK or Kir4.1) are expressed in the late DCT and play an important role in mediating K+ secretion, the aim of the present study is to test whether ROMK and ENaC activity in the DCT/CNT are also compromised in the mice expressing PHAII mutant Wnk4. Western blot analysis shows that the expression of βENaC and γENaC subunits but not αENaC subunit was lower in TgWnk4PHAII mice than that in wild-type (WT) and TgWnk4WT mice. Patch-clamp experiments detected amiloride-sensitive Na+ currents and TPNQ-sensitive K+ currents in DCT2/CNT, suggesting the activity of ENaC and ROMK. However, both Na+ and ROMK currents in DCT2/CNT of TgWnk4PHAII mice were significantly smaller than those in WT and TgWnk4WT mice. In contrast, the basolateral K+ currents in the DCT were similar among three groups, despite higher NCC expression in TgWnk4PHAII mice than those of WT and TgWnk4WTmice. An increase in dietary K+ intake significantly increased both ENaC and ROMK currents in the DCT2/CNT of all three groups. However, high-K+ (HK) intake-induced stimulation of Na+ and K+ currents was smaller in TgWnk4PHAII mice than those in WT and TgWnk4WT mice. We conclude that ENaC and ROMK channel activity in DCT2/CNT are inhibited in TgWnk4PHAII mice and that Wnk4PHAII-induced inhibition of ENaC and ROMK may contribute to the suppression of K+ secretion in the DCT2/CNT in addition to increased NCC activity.

Keywords: K secretion; Kir1.1; Kir4.1; hyperkalemia; pseudohypoaldosteronism type II.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Disease Models, Animal
  • Down-Regulation
  • Epithelial Sodium Channels / genetics
  • Epithelial Sodium Channels / metabolism*
  • Female
  • Genetic Predisposition to Disease
  • Hyperkalemia / genetics
  • Hyperkalemia / metabolism
  • Kidney Tubules, Distal / metabolism*
  • Liddle Syndrome / genetics
  • Liddle Syndrome / metabolism*
  • Male
  • Membrane Potentials
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Phenotype
  • Potassium / metabolism*
  • Potassium Channels, Inwardly Rectifying / genetics
  • Potassium Channels, Inwardly Rectifying / metabolism*
  • Potassium, Dietary / administration & dosage
  • Potassium, Dietary / metabolism
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Renal Elimination
  • Signal Transduction

Substances

  • Epithelial Sodium Channels
  • Kcnj1 protein, mouse
  • Potassium Channels, Inwardly Rectifying
  • Potassium, Dietary
  • Scnn1b protein, mouse
  • Scnn1g protein, mouse
  • Prkwnk4 protein, mouse
  • Protein-Serine-Threonine Kinases
  • Potassium