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Abstract: SA-PO1042

WNK4 Acts on Thick Ascending Limbs In Vivo as Well as Distal Convoluted Tubules

Session Information

  • Na+, K+, Cl-
    November 04, 2017 | Location: Hall H, Morial Convention Center
    Abstract Time: 10:00 AM - 10:00 AM

Category: Fluid, Electrolytes, and Acid-Base

  • 703 Na+, K+, Cl- Basic

Authors

  • Terker, Andrew, OHSU, Portland, Oregon, United States
  • Erspamer, Kayla J., Oregon Health & Science University, Portland, Oregon, United States
  • Miller, Lauren N, Oregon Health and Science University, Portland, Oregon, United States
  • Ferdaus, Mohammed Zubaerul, Oregon Health & Science University, Portland, Oregon, United States
  • Wang, WenHui, New York Medical College, Valhalla, New York, United States
  • Su, Xiao-Tong, New York Medical College, Valhalla, New York, United States
  • Cornelius, Ryan J., Oregon Health and Science University, Portland, Oregon, United States
  • McCormick, James A., Oregon Health & Science University, Portland, Oregon, United States
  • Gamba, Gerardo, Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Tlalpan, Mexico City, Mexico
  • Yang, Chao-Ling, Oregon Health and Science University, Portland, Oregon, United States
  • Ellison, David H., Oregon Health & Science University, Portland, Oregon, United States
Background

WNK4 mutations increase thiazide-sensitive NaCl cotransporter (NCC) activity in the distal convoluted tubule (DCT) and cause familial hyperkalemic hypertension (FHHt). Conversely, WNK4 knockout (KO) in mice leads to a 'Gitelman-like' phenotype', similar to loss of NCC function. Even though the WNK/SPAK-OxSR1 pathway can modulate the Na-K-2Cl cotransporter (NKCC2) in vitro, effects of WNK4 KO on NKCC2 were not noted in mice. Yet WNK4 knockout mice are not hypocalciuric, a cardinal feature of NCC dysfunction, suggesting a mixed phenotype. To test this, we revisited the phenotypes of WNK4 KO and WNK4 activation (WNK4Q562E) in mice.

Methods

Plasma and urine electrolyte concentrations from WNK4 KO and WNK4Q562E mice were determined. Western blots determined protein abundance. Modified diets were reported previously. NKCC2 and NCC activity were assessed with furosemide (25mg/kg IP) and hydrochlorothiazide (25mg/kg IP).

Results

As reported previously, plasma potassium and chloride were significantly lower in WNK4 KO mice than in controls, but urine calcium excretion was normal. A high salt/high K+ diet increased urine calcium in control mice, compared with high salt/normal K+, but not in WNK4 KO (interaction p=0.0183). WNK4 KO mice exhibited low total and phosphorylated NCC, compared with controls, as expected, but also exhibited low phosphorylated NKCC2 (total NKCC2 was normal). In contrast, WNK4Q562E mice had more phosphorylated NKCC2 than controls. The response to furosemide, an index of NKCC2 function, was similar in WNK4 KO and control, but we reasoned that this may have reflected compensatory NCC activation in controls. When compensatory DCT transport was inhibited with thiazide, however, the response to furosemide was significantly lower in WNK4 KO mice than in controls, consistent with reduced NKCC2 activity.

Conclusion

While WNK4 clearly has predominant effects on NCC, it also modulates NKCC2 in vivo. Thus, although WNK4 deficiency has been suggested to cause a mild 'Gitelman-like phenotype', it much more closely mimics Bartter syndrome type III, with a mixed thick ascending limb and DCT phenotype. WNK4-mediated FHHt likely also involves activation of both NCC and NKCC2, accounting for variable reports of furosemide action in some cases.

Funding

  • NIDDK Support