Abstract: FR-OR125

The A-Splice Variant of NBCe1 (NBCe1-A) Is Necessary for the Renal Ammonia and K Response to Hypokalemia

Session Information

Category: Fluid, Electrolytes, and Acid-Base

  • 701 Acid-Base: Basic

Authors

  • Lee, Hyun-Wook, University of Florida, Gainesville, Florida, United States
  • Osis, Gunars, University of Florida, Gainesville, Florida, United States
  • Harris, Autumn N, University of Florida, Gainesville, Florida, United States
  • Webster, Kierstin L, University of Florida, Gainesville, Florida, United States
  • Holmes, Heather L., Mayo Clinic College of Medicine, Rochester, Minnesota, United States
  • Rossano, Adam Joseph, Mayo Clinic College of Medicine, Rochester, Minnesota, United States
  • Romero, Michael F., Mayo Clinic College of Medicine, Rochester, Minnesota, United States
  • Verlander, Jill W., University of Florida, Gainesville, Florida, United States
  • Weiner, I. David, University of Florida, Gainesville, Florida, United States
Background

Hypokalemia is associated with increased ammonia excretion, but neither the specific proteins that signal this response nor the functional role of increased ammonia excretion are known. This study’s purpose was to determine NBCe1-A’s role in the effect of hypokalemia on renal ammonia metabolism and potassium homeostasis.

Methods

We used mice with NBCe1-A deletion generated using TALEN techniques. We compared mice with homozygous deletion (KO) to wild-type (WT) littermates. Hypokalemia was induced by feeding a K-free diet for 7 days.

Results

A K-free diet caused persistently increased urinary ammonia excretion in WT mice, whereas in KO mice urinary ammonia increased only on day 1 and 2, and then returned to baseline. In proximal convoluted tubule (PCT), NBCe1-A KO had significantly lower expression, compared to WT, of key ammoniagenic proteins, phosphoenolpyruvate carboxykinase (PEPCK) and phosphate-dependent glutaminase (PDG), and greater expression of the ammonia-recycling protein, glutamine synthetase (GS). In contrast, in the proximal straight tubule (PST) in the outer medulla, where relatively little NBCe1-A expression is found compared to the PCT, hypokalemic KO mice exhibited PEPCK and PDG expression that was greater and GS expression that was less than in hypokalemic WT. NBCe1-A deletion also altered renal K handling during hypokalemia. Serum K did not differ on normal diet, but was lower in KO mice on K-free diet (KO 1.8±0.1; WT 3.2±0.1 mM, P<0.01). Despite more severe hypokalemia, urinary K was significantly higher, 75%±16% greater in KO than WT during days 3-7, when maximal K conservation occurred in both WT and KO. Total NCC expression was unchanged, but phospho-NCC, which decreases renal K excretion, was significantly less in hypokalemic KO than WT mice.

Conclusion

1) NBCe1-A is essential to the signaling pathway that increases ammonia excretion in response to hypokalemia; 2) KO mice partially compensate to NBCe1-A deletion with supranormal responses in PST; and, 3) NBCe1-A is critical for PT signaling to distal sites to conserve K through a mechanism that may involve NCC phosphorylation. Thus, hypokalemia’s induction of ammonia metabolism via NBCe1 may be a critical signaling mechanism regulating distal epithelial K transport.

Funding

  • NIDDK Support