Kidney Week

Abstract: TH-PO312

NBCe1-B/C Knockout Mice Exhibit an Impaired Respiratory Response to Metabolic Acidosis Resulting in Increased Ammonia Excretion

Session Information

• Fluid, Electrolyte, and Acid-Base Disorders: Basic
  November 03, 2022 | Location: Exhibit Hall, Orange County Convention Center‚ West Building
  Abstract Time: 10:00 AM - 12:00 PM

Category: Fluid‚ Electrolyte‚ and Acid-Base Disorders

• 1001 Fluid‚ Electrolyte‚ and Acid-Base Disorders: Basic

Authors

• Brady, Clayton, University at Buffalo Jacobs School of Medicine and Biomedical Sciences, Buffalo, New York, United States

Clayton Brady,

• Parker, Mark, University at Buffalo Jacobs School of Medicine and Biomedical Sciences, Buffalo, New York, United States

Mark Parker,

Background

Sodium-bicarbonate cotransporter variants NBCe1-B and NBCe1-C (NBCe1-B/C) are expressed in the brainstem while variants NBCe1-A and NBCe1-B are expressed in the proximal tubule. NBCe1-A is the primary renal variant and is important to the kidney response to metabolic acidosis (MAc). Less understood is the role of NBCe1-B/C, but they are thought to play a role in both the respiratory and renal responses to MAc. We tested this hypothesis in NBCe1-B/C knockout (KO_b/c) mice.

Methods

We validated an NBCe1-B/C specific antibody and used it to confirm the presence/absence of NBCe1-B in the kidney and NBCe1-B/C in the brainstem of WT and KO_b/c mice. MAc was induced by adding 0.5% sucrose + 0.28M NH₄Cl to drinking water. The abundance response of kidney NBCe1-B to MAc was quantified in WT mice by western blot. To assess the effect of MAc on acid-base status, WT and KO_b/c mice were subjected to control (0.5% sucrose in drinking water) or MAc conditions for 1-3 days followed by cardiac puncture and blood-gas/electrolyte analysis. 24-hour urine collections were assessed for ammonia excretion, titratable acid (TA) excretion, and pH. The respiratory response was assessed using whole-body plethysmography, with WT and KO_b/c mice assessed each day of a 3-day MAc-challenge.

Results

After 3-days of MAc, NBCe1-B kidney abundance was 3.6x that of controls in WT mice, supporting evidence of a role for NBCe1-B in the kidney during MAc. Surprisingly, however, KO_b/c mice had a greater recovery in plasma [HCO₃^-] and higher pCO₂ levels, but a similar recovery in plasma pH to WT mice. This was associated with a greater increase in ammonia excretion in KO_b/c males but not females, whereas there were no differences in changes in TA excretion or urine pH between WT and KO_b/c mice. In regards to the respiratory response, over the 3-day MAc challenge WT mice exhibited a maximum increase in minute volume of 10% whereas in KO_b/c mice minute volume did not significantly change.

Conclusion

The impaired respiratory response to MAc in KO_b/c mice leads to elevated ammonia excretion and a greater recovery in plasma [HCO₃^-]. We suggest this is because, although normally the respiratory response to MAc lowers pCO₂ in order to help maintain plasma pH, this decrease in pCO₂ also has an inhibitory effect on renal ammoniagenesis.

Funding

• NIDDK Support