ASN's Mission

ASN leads the fight to prevent, treat, and cure kidney diseases throughout the world by educating health professionals and scientists, advancing research and innovation, communicating new knowledge, and advocating for the highest quality care for patients.

learn more

Contact ASN

1401 H St, NW, Ste 900, Washington, DC 20005

email@asn-online.org

202-640-4660

The Latest on Twitter

Kidney Week

Abstract: PO1093

Role of mTORC2/SGK1 Signaling in Rapid Response to Acute K Load to Maintain K+ Homeostasis

Session Information

Category: Fluid, Electrolyte, and Acid-Base Disorders

  • 901 Fluid, Electrolyte, and Acid-Base Disorders: Basic

Authors

  • Saha, Bidisha, University of California San Francisco, San Francisco, California, United States
  • Shabbir, Waheed, University of California San Francisco, San Francisco, California, United States
  • Takagi, Enzo, University of California San Francisco, San Francisco, California, United States
  • Demko, John E., University of California San Francisco, San Francisco, California, United States
  • Sorensen, Mads Vaarby, Aarhus Universitet, Aarhus, Midtjylland, Denmark
  • Leite-Dellova, Deise C A, University of California San Francisco, San Francisco, California, United States
  • Pearce, David, University of California San Francisco, San Francisco, California, United States
Background

The kinase mTORC2 phosphorylates SGK1 and is required for normal K+ secretion in the aldosterone-sensitive distal nephron. Aldosterone is known to play a role in mediating a sustained response through effects on SGK1 gene transcription, however, it is unknown how rapid responses are mediated. Here we have explored the role of mTORC2 and ENaC activity in the early response to an acute K+ load to regulate K secretion.

Methods

Inducible tubule-specific Rictor (a core component of mTORC2) knockout mice (TRKO) were generated (Pax8-rtTA/LC-1/Rictorflox/flox). Both WT and TRKO mice received control or 2% KCl via gavage following intraperitoneal vehicle or Benzamil (ENaC inhibitor) injection. Spot urine was collected. ENaC and ROMK activity were measured in split open tubules by apical membrane patch clamp 3h post gavage. Membrane and cytoplasmic proteins were extracted from kidneys for immunoblot analysis.

Results

Adult TRKO mice on normal diet displayed no abnormality except significantly elevated aldosterone. K+ administration by gavage triggered markedly greater Na+ excretion and lower K+ excretion in TRKO than WT mice, with differences detectable within 1 h of gavage. Benzamil induced a greater natriuresis in WT than in TRKO mice, and more strongly suppressed kaliuresis, consistent with greater ENaC activation in WT than in TRKO. The response of WT occurred rapidly, before significant change in aldosterone. In benzamil-treated mice, the natriuresis and kaliuresis of WT and TRKO mice were comparable, strongly supporting the idea that KCl induced ENaC-dependent K+ secretion in WT, and that this response is defective in TRKO. Patch clamp measurement demonstrated increased ENaC activity in WT but not in TRKO mice and no change in ROMK activity in WT or TRKO by KCl gavage. Membrane expression of cleaved α- and gENaC were significantly increased in WT but not in TRKO mice receiving KCl gavage. No significant increase in membrane expression of ROMK was observed in WT or TRKO post gavage. Finally, both SGK1 and Nedd4-2 phosphorylation were increased in WT but not TRKO mice receiving KCl gavage.

Conclusion

Overall, the data strongly suggest that an acute K+ load acts through mTORC2/SGK1 to rapidly stimulate ENaC but not ROMK to promote K+ secretion. These effects are primarily due to local renal tubular K+ sensing.

Funding

  • NIDDK Support