Mechanisms for the Potassium Sparing Effects of Furosemide in Mice on High Potassium Diets

Author

Bangchen Wang, University of Nebraska Medical CenterFollow

Graduation Date

Spring 5-5-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Cellular & Integrative Physiology

First Advisor

Steven C. Sansom

Abstract

Because of its cardio-protective benefits, diets that are low in Na⁺ and high in K⁺ are often warranted in conjunction with use of diuretics such as furosemide for treating hypertension. It is critical to understand how such diets influence the diuretic actions on renal K⁺ handling in order to choose the best drug for patients.

Furosemide is a commonly used K-wasting diuretic. It increases urinary K⁺ excretion by increasing distal Na⁺ delivery that stimulates K⁺ secretion. However, in wild-type mice (WT) adapted to an alkaline low Na⁺ high K⁺ diet (LNaHK), both 12-hour IP furosemide injection and 7-day furosemide water treatment decreased renal K⁺ clearance. We hypothesized that there is furosemide-sensitive net K⁺ secretion in WT adapted to LNaHK. Free-flow micropuncture experiments showed that furosemide increased [K⁺] in the early distal tubule (EDT [K⁺]) in WT on a regular diet (RD) but decreased EDT [K⁺] in WT on LNaHK. Furosemide did not affect EDT [K⁺] in ROMK knockout mice (ROMK KO) on LNaHK or WT on an alkaline normal Na⁺ high K⁺ diet (HK). Furosemide-sensitive Na⁺ excretion was significantly greater in mice on LNaHK than those on RD or HK. Patch clamp analysis of split-open thick ascending limbs (TAL) revealed that the 70-pS ROMK channel exhibited a higher open probability (Po) but similar density in WT on LNaHK, compared to WT on RD. These results indicate that mice adapted to LNaHK exhibit furosemide-sensitive net K⁺ secretion in the TAL that is dependent on increased NKCC2 activity and mediated by ROMK channels.

Furosemide acidifies the urine by increasing acid secretion via the Na⁺-H⁺ exchanger 3 (NHE3) in TAL and vacuolar H⁺-ATPase (V-ATPase) in the distal nephron. Because alkaline urine is required for BK-αβ4-mediated K⁺ secretion, we hypothesized that furosemide reduces BK-αβ4-mediated K⁺ secretion by acidifying the urine. Furosemide water treatment for 11 days led to decreased urine pH in both WT and BK-β4 knockout mice (BK-β4 KO) with increased V-ATPase expression and elevated plasma aldosterone levels. However, furosemide water decreased renal K⁺ clearance and elevated plasma [K⁺] in WT but not BK-β4 KO. Addition of acetazolamide in furosemide water restored urine pH along with renal K⁺ clearance and plasma [K⁺] to similar levels as control group. Additionally, western blotting and immunofluorescence staining showed that furosemide decreased cortical expression of BK-β4 and reduced apical localization of BK-α in connecting tubules (CNT); they were restored by adding acetazolamide to furosemide water. These results indicate that in mice adapted to HK, furosemide reduces BK-αβ4-mediated K⁺ secretion by acidifying the urine.

In conclusion, by inhibiting net K⁺ secretion in the TAL and BK-αβ4-mediated K⁺ secretion in CNT, furosemide acts as a K-sparing diuretic in mice adapted to LNaHK and HK.

Recommended Citation

Wang, Bangchen, "Mechanisms for the Potassium Sparing Effects of Furosemide in Mice on High Potassium Diets" (2018). Theses & Dissertations. 281.
https://digitalcommons.unmc.edu/etd/281