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Abstract: FR-OR30

ENaC Inhibition with Trimethoprim Occurs Without Changing Urinary H+ Excretion

Session Information

Category: Fluid, Electrolytes, and Acid-Base Disorders

  • 1101 Fluid, Electrolyte, and Acid-Base Disorders: Basic


  • Ayasse, Niklas, Universitatsklinikum Mannheim, Mannheim, Baden-Württemberg, Germany
  • Berg, Peder, Aarhus Universitet, Aarhus, Midtjylland, Denmark
  • Svendsen, Samuel L.C., Aarhus Universitet, Aarhus, Midtjylland, Denmark
  • Rousing, Amalie Quist, Aarhus Universitet, Aarhus, Midtjylland, Denmark
  • Sorensen, Mads Vaarby, Aarhus Universitet, Aarhus, Midtjylland, Denmark
  • Fedosova, Natalya U., Aarhus Universitet, Aarhus, Midtjylland, Denmark
  • Leipziger, Jens G., Aarhus Universitet, Aarhus, Midtjylland, Denmark

There is growing consensus that collecting duct H+ secretion occurs independent of changes in the transepithelial voltage (Vte). We recently identified a new mechanism how benzamil stimulates acute urinary alkalization. In addition to its direct inhibition of the epithelial sodium channel (ENaC), benzamil acutely impairs H+ excretion by blocking the H+/K+ ATPase. The latter effect explains benzamil's acute and marked effect on urine alkalization. However, the question remained whether inhibition of ENaC activity causes alterations in renal H+ excretion. To revisit this question, we studied the effect of a direct ENaC inhibitor which is structurally different from benzamil. Here, we chose the antibiotic molecule trimethoprim, well-known to cause K+ retention by direct ENaC inhibition.


In vivo experiments were performed in bladder-catheterized C57BL/6J mice, allowing real-time measurement of urinary pH, electrolyte, and acid excretion. Trimethoprim was administered as an intraperitoneal bolus injection (5 µg/g bw). Additionally, the effect of trimethoprim on H+/K+-ATPase activity was assessed in vitro in pig gastric H+/K+ ATPase enriched membrane vesicles under different pH and extracellular K+ concentrations.


We find that trimethoprim inhibits ENaC, acutely increasing natriuresis and decreasing kaliuresis, thus confirming earlier studies. However, trimethoprim had no effect on urinary pH or net acid excretion, contrasting the effects of benzamil that acutely alkalizes the urine and reduces net acid excretion. Moreover, in vitro experiments on isolated pig gastric H+/K+-ATPase proteins showed near to no effect of trimethoprim on the pump's activity, again contrasting the action of benzamil.


In comparison to benzamil, that inhibits both ENaC and the H+/K+-ATPase proteins, the renal action of trimethoprim appears to be confined to ENaC inhibition. These findings further support the hypothesis that inhibition of ENaC does not cause inhibition of H+ secretion in the collecting duct. Thus, these results add an additional argument refuting the hypothesis of voltage-dependent H+ secretion in collecting duct.


  • Government Support – Non-U.S.