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Mutchler SM, Whelan SCM, Marciszyn A, Chen J, Kleyman TR, Shi S. Role of paraoxonase 3 in regulating ENaC-mediated Na + transport in the distal nephron. J Physiol 2024; 602:737-757. [PMID: 38345534 PMCID: PMC10940207 DOI: 10.1113/jp285034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Accepted: 01/11/2024] [Indexed: 02/18/2024] Open
Abstract
Paraoxonase 3 (PON3) is expressed in the aldosterone-sensitive distal nephron, where filtered Na+ is reabsorbed mainly via the epithelial Na+ channel (ENaC) and Na+ -coupled co-transporters. We previously showed that PON3 negatively regulates ENaC through a chaperone mechanism. The present study aimed to determine the physiological role of PON3 in renal Na+ and K+ homeostasis. Pon3 knockout (KO) mice had higher amiloride-induced natriuresis and lower plasma [K+ ] at baseline. Single channel recordings in split-open tubules showed that the number of active channels per patch was significantly higher in KO mice, resulting in a higher channel activity in the absence of PON3. Although whole kidney abundance of ENaC subunits was not altered in Pon3 KOs, ENaC gamma subunit was more apically distributed within the connecting tubules and cortical collecting ducts of Pon3 KO kidneys. Additionally, small interfering RNA-mediated knockdown of PON3 in cultured mouse cortical collecting duct cells led to an increased surface abundance of ENaC gamma subunit. As a result of lower plasma [K+ ], sodium chloride co-transporter phosphorylation was enhanced in the KO kidneys, a phenotype that was corrected by a high K+ diet. Finally, PON3 expression was upregulated in mouse kidneys under dietary K+ restriction, potentially providing a mechanism to dampen ENaC activity and associated K+ secretion. Taken together, our results show that PON3 has a role in renal Na+ and K+ homeostasis through regulating ENaC functional expression in the distal nephron. KEY POINTS: Paraoxonase 3 (PON3) is expressed in the distal nephron of mouse kidneys and functions as a molecular chaperone to reduce epithelial Na+ channel (ENaC) expression and activity in heterologous expression systems. We examined the physiological role of PON3 in renal Na+ and K+ handling using a Pon3 knockout (KO) mouse model. At baseline, Pon3 KO mice had lower blood [K+ ], more functional ENaC in connecting tubules/cortical collecting ducts, higher amiloride-induced natriuresis, and enhanced sodium chloride co-transporter (NCC) phosphorylation. Upon challenge with a high K+ diet, Pon3 KO mice had normalized blood [K+ ] and -NCC phosphorylation but lower circulating aldosterone levels compared to their littermate controls. Kidney PON3 abundance was altered in mice under dietary K+ loading or K+ restriction, providing a potential mechanism for regulating ENaC functional expression and renal Na+ and K+ homeostasis in the distal nephron.
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Affiliation(s)
| | | | - Allison Marciszyn
- Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Jingxin Chen
- Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Thomas R. Kleyman
- Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Cell Biology, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Shujie Shi
- Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
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Ayasse N, Berg P, Svendsen SL, Rousing AQ, Sørensen MV, Fedosova NU, Leipziger J. Trimethoprim inhibits renal H +-K +-ATPase in states of K + depletion. Am J Physiol Renal Physiol 2024; 326:F143-F151. [PMID: 37942538 DOI: 10.1152/ajprenal.00273.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Revised: 10/23/2023] [Accepted: 11/06/2023] [Indexed: 11/10/2023] Open
Abstract
There is growing consensus that under physiological conditions, collecting duct H+ secretion is independent of epithelial Na+ channel (ENaC) activity. We have recently shown that the direct ENaC inhibitor benzamil acutely impairs H+ excretion by blocking renal H+-K+-ATPase. However, the question remains whether inhibition of ENaC per se causes alterations in renal H+ excretion. To revisit this question, we studied the effect of the antibiotic trimethoprim (TMP), which is well known to cause K+ retention by direct ENaC inhibition. The acute effect of TMP (5 µg/g body wt) was assessed in bladder-catheterized mice, allowing real-time measurement of urinary pH, electrolyte, and acid excretion. Dietary K+ depletion was used to increase renal H+-K+-ATPase activity. In addition, the effect of TMP was investigated in vitro using pig gastric H+-K+-ATPase-enriched membrane vesicles. TMP acutely increased natriuresis and decreased kaliuresis, confirming its ENaC-inhibiting property. Under control diet conditions, TMP had no effect on urinary pH or acid excretion. Interestingly, K+ depletion unmasked an acute urine alkalizing effect of TMP. This finding was corroborated by in vitro experiments showing that TMP inhibits H+-K+-ATPase activity, albeit at much higher concentrations than benzamil. In conclusion, under control diet conditions, TMP inhibited ENaC function without changing urinary H+ excretion. This finding further supports the hypothesis that the inhibition of ENaC per se does not impair H+ excretion in the collecting duct. Moreover, TMP-induced urinary alkalization in animals fed a low-K+ diet highlights the importance of renal H+-K+-ATPase-mediated H+ secretion in states of K+ depletion.NEW & NOTEWORTHY The antibiotic trimethoprim (TMP) often mediates K+ retention and metabolic acidosis. We suggest a revision of the underlying mechanism that causes metabolic acidosis. Our results indicate that TMP-induced metabolic acidosis is secondary to epithelial Na+ channel-dependent K+ retention. Under control dietary conditions, TMP does not per se inhibit collecting duct H+ secretion. These findings add further argument against a physiologically relevant voltage-dependent mechanism of collecting duct H+ excretion.
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Affiliation(s)
- Niklas Ayasse
- Department of Biomedicine, Physiology, Aarhus University, Aarhus, Denmark
- Vth Department of Medicine, University Hospital Mannheim, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany
| | - Peder Berg
- Department of Biomedicine, Physiology, Aarhus University, Aarhus, Denmark
| | - Samuel L Svendsen
- Department of Biomedicine, Physiology, Aarhus University, Aarhus, Denmark
| | | | | | - Natalya U Fedosova
- Department of Biomedicine, Physiology, Aarhus University, Aarhus, Denmark
| | - Jens Leipziger
- Department of Biomedicine, Physiology, Aarhus University, Aarhus, Denmark
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Xue J, Thomas L, Dominguez Rieg JA, Fenton RA, Rieg T. NHE3 in the thick ascending limb is required for sustained but not acute furosemide-induced urinary acidification. Am J Physiol Renal Physiol 2022; 323:F141-F155. [PMID: 35635321 PMCID: PMC9306792 DOI: 10.1152/ajprenal.00013.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The Na+/H+ exchanger isoform 3 (NHE3) facilitates Na+ reabsorption and H+ secretion by the kidneys. Despite stronger NHE3 abundance in the thick ascending limb (TAL) compared to the S1 and S2 segments of the proximal tubule, the role of NHE3 in the TAL is poorly understood. To investigate the role of NHE3 in the TAL, we generated and phenotyped TAL-specific NHE3 knockout mice (NHE3TAL-KO). Compared to control mice, NHE3TAL-KO mice did not show significant differences in body weight, blood pH or plasma Na+, K+ or Cl- levels. Fluid intake trended to be higher and urine osmolality was significantly lower in NHE3TAL-KO mice. Despite a similar GFR, NHE3TAL-KO mice had a greater urinary K+/creatinine ratio. One proposed role of NHE3 relates to furosemide-induced urinary acidification. Acute bolus treatment with furosemide under anesthesia did not result in differences in the dose dependence of urinary flow rate, Cl- excretion or maximal urinary acidification between genotypes; however, in contrast to control mice, urinary pH returned immediately towards baseline levels in NHE3TAL-KO mice. Chronic furosemide treatment reduced urine osmolality similarly in both genotypes but metabolic alkalosis, hypokalemia and calciuresis were absent in NHE3TAL-KO mice. Compared to vehicle, chronic furosemide treatment in control mice resulted in greater NKCC2 and lower Npt2a abundances, effects that were absent in NHE3TAL-KO mice. In summary, NHE3 in the TAL plays a role for the sustained acidification effect of furosemide. Consistent with this, long-term treatment with furosemide did not result in metabolic alkalosis in NHE3TAL-KO mice.
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Affiliation(s)
- Jianxiang Xue
- Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, Florida, United States
| | - Linto Thomas
- Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, Florida, United States
| | - Jessica A Dominguez Rieg
- Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, Florida, United States.,James A. Haley Veterans' Hospital, Tampa, Florida, United States
| | - Robert A Fenton
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Timo Rieg
- Department of Molecular Pharmacology and Physiology, Morsani College of Medicine, University of South Florida, Tampa, Florida, United States.,James A. Haley Veterans' Hospital, Tampa, Florida, United States.,Hypertension and Kidney Research Center, University of South Florida, Tampa, FL, United States
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Svendsen SL, Kornvig S, Berg P, Jensen IS, Araujo IBBA, Larsen CK, Leipziger J, Sørensen MV. Dietary K + acts as a genuine diuretic. Acta Physiol (Oxf) 2022; 234:e13762. [PMID: 34984847 DOI: 10.1111/apha.13762] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 11/29/2021] [Accepted: 01/01/2022] [Indexed: 12/11/2022]
Abstract
K+ balance in mammals relies on regulated renal K+ excretion matching unregulated fluctuating K+ intake. Upon a K+ rich meal, rapid and powerful K+ excretion is needed. Renal K+ secretion is stimulated by the increased tubular flow. We speculated that high K+ intake acutely increases urinary flow to stimulate K+ excretion. METHODS Mice were K+ challenged through diets or gavage. Post K+ loading urinary output, osmolarity, [K+ ]u , [Na+ ]u , plasma osmolarity, [copeptin]p , [K+ ]p , and [Na+ ]p were measured. To locate the mechanism of K+ -induced diuresis in the glomerular/tubular system we measured creatinine excretion and assessed functional transport in isolated perfused TALs and CDs during an acute [K+ ]bl switch from 3.6 to 6.5 mM. Molecular adaptations of transport proteins involved in water reabsorption were investigated by immunoblotting. RESULTS (1) Mice switched from a 1% to 2% K+ diet increased diuresis within 12 hours and reciprocally reduced diuresis when switched from 1% to 0.01% K+ diet. (2) A single K+ gavage load, corresponding to 25%-50% of daily K+ intake, induced 100% increase in diuresis within 30 minutes. This occurred despite augmented plasma osmolarity and AVP synthesis. (3) K+ gavage did not change GFR. (4) In isolated perfused TALs, shifting [K+ ]bl from 3.6 to 6.5 mM did not affect AVP-induced NaCl transport. (5) In sharp contrast, in isolated perfused CDs, shifting [K+ ]bl from 3.6 to 6.5 mM markedly reduced CD AVP sensitivity, ie inhibited water absorption. CONCLUSION Dietary K+ loading induces a rapidly on-setting diuresis. The mechanism of K+ -induced diuresis involves desensitization of the CD to AVP.
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Affiliation(s)
- Samuel L. Svendsen
- Department of Biomedicine, Physiology, Health Aarhus University Aarhus C Denmark
| | - Simon Kornvig
- Department of Biomedicine, Physiology, Health Aarhus University Aarhus C Denmark
| | - Peder Berg
- Department of Biomedicine, Physiology, Health Aarhus University Aarhus C Denmark
| | - Iben S. Jensen
- Department of Biomedicine, Physiology, Health Aarhus University Aarhus C Denmark
| | | | - Casper K. Larsen
- Department of Biomedicine, Physiology, Health Aarhus University Aarhus C Denmark
| | - Jens Leipziger
- Department of Biomedicine, Physiology, Health Aarhus University Aarhus C Denmark
| | - Mads V. Sørensen
- Department of Biomedicine, Physiology, Health Aarhus University Aarhus C Denmark
- Aarhus Institute for Advanced Studies (AIAS) Aarhus University Aarhus C Denmark
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Pearce D, Manis AD, Nesterov V, Korbmacher C. Regulation of distal tubule sodium transport: mechanisms and roles in homeostasis and pathophysiology. Pflugers Arch 2022; 474:869-884. [PMID: 35895103 PMCID: PMC9338908 DOI: 10.1007/s00424-022-02732-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Revised: 07/09/2022] [Accepted: 07/11/2022] [Indexed: 02/03/2023]
Abstract
Regulated Na+ transport in the distal nephron is of fundamental importance to fluid and electrolyte homeostasis. Further upstream, Na+ is the principal driver of secondary active transport of numerous organic and inorganic solutes. In the distal nephron, Na+ continues to play a central role in controlling the body levels and concentrations of a more select group of ions, including K+, Ca++, Mg++, Cl-, and HCO3-, as well as water. Also, of paramount importance are transport mechanisms aimed at controlling the total level of Na+ itself in the body, as well as its concentrations in intracellular and extracellular compartments. Over the last several decades, the transporters involved in moving Na+ in the distal nephron, and directly or indirectly coupling its movement to that of other ions have been identified, and their interrelationships brought into focus. Just as importantly, the signaling systems and their components-kinases, ubiquitin ligases, phosphatases, transcription factors, and others-have also been identified and many of their actions elucidated. This review will touch on selected aspects of ion transport regulation, and its impact on fluid and electrolyte homeostasis. A particular focus will be on emerging evidence for site-specific regulation of the epithelial sodium channel (ENaC) and its role in both Na+ and K+ homeostasis. In this context, the critical regulatory roles of aldosterone, the mineralocorticoid receptor (MR), and the kinases SGK1 and mTORC2 will be highlighted. This includes a discussion of the newly established concept that local K+ concentrations are involved in the reciprocal regulation of Na+-Cl- cotransporter (NCC) and ENaC activity to adjust renal K+ secretion to dietary intake.
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Affiliation(s)
- David Pearce
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA USA
| | - Anna D. Manis
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA USA
| | - Viatcheslav Nesterov
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany, Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany, Erlangen, Germany
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