Renal NHE1 is required for regulation of intracellular pH in principal cells and type B intercalated cells

Abstract

The sodium-hydrogen exchanger isoform 1 (NHE1) is a plasma membrane transporter with roles in transepithelial Na+/H+ transport, intracellular pH (pHi) and cell volume regulation. Within the kidney, NHE1 is previously documented to be expressed in all nephron segments. However, recent transcriptomic and proteomic analyses, and our staining results in mice, consistently find no expression of NHE1 in the proximal tubule or thick ascending limb, but in the distal nephron, including distal convoluted tubule, connecting tubule, and collecting duct (principal and intercalated cells, PC and IC, respectively). We hypothesized that basolateral NHE1 in IC (co-labelling with H+-ATPase B1 subunit, labeling all 3 types of IC: type A, B, and non-A-non-B) plays an important role in acid-base homeostasis. Due to lack of a suitable animal model, we generated kidney-specific NHE1 knockout (NHE1KS-KO) mice. NHE1KS-KO mice completely lack renal NHE1 protein expression compared to their control littermates (n=6 male mice/genotype). No differences were observed in body weight, food and water intake (determined in their home cages) or concentrations of blood Na+, K+, Ca2+, pH or HCO3-. Urine analysis showed no significant differences in electrolytes, minerals of pH. To mechanistically determine the role of NHE1 for pHi regulation in IC and PC we used confocal microscopy of acutely-split open cortical collecting ducts. This method allows for the analysis of a vast number of PC/IC simultaneously. To study the role of NHE1 we employed a NH4Cl pre-pulse (40 mM) and measured pHi recovery after switching back to a physiological solution. Intracellular pH recovery in PC (n=171) was significantly slower (~50%) in NHE1KS-KO mice compared to controls (n=85). Similar to PC, pHi recovery in type B IC of NHE1KS-KO mice (n=38) was significantly slower (~35%) compared to controls (n=40). No differences in type A IC were observed between NHE1KS-KO mice (n=35) and controls (n=29). Inhibition of ClC-K2 via NPPB (Cl-channel blocker) was used to confirm cell types: PC did not respond with a change in pHi but NPPB increased pHi in type A and decreased pHi in type B ICs. In summary, our results identify for the first time an important role of NHE1 for pHi regulation particularly in PCs and type B ICs. Funding to Dr. Rieg was provided by the NIDDK grant 1R01DK110621, VA Merit Review Award IBX004968A, AHA Transformational Research Award 19TPA34850116, and NIDDK Diabetic Complications Consortium grants DK076169 and DK115255. DK095029 and DK117865 (both to O. Pochynyuk). Dr. Thomas was supported by an AHA postdoctoral grant (828731), V. Tomilin by an AHA Career Development Award 19CDA34660148. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.