scholarly journals Potassium-sparing effects of furosemide in mice on high-potassium diets

2019 ◽  
Vol 316 (5) ◽  
pp. F970-F973
Author(s):  
Bangchen Wang ◽  
Steven C. Sansom
Keyword(s):  
Bk Channel ◽  
Na Channel ◽  
Thick Ascending Limb ◽  
Distal Nephron ◽  
High Potassium ◽  
Henle's Loop ◽  
High K ◽  
K Secretion ◽  
K Concentration ◽  
Sites Of Action

In individuals on a regular “Western” diet, furosemide induces a kaliuresis and reduction in plasma K concentration by inhibiting Na reabsorption in the thick ascending limb of Henle’s loop, enhancing delivery of Na to the aldosterone-sensitive distal nephron. In the aldosterone-sensitive distal nephron, the increased Na delivery stimulates K wasting due to an exaggerated exchange of epithelial Na channel-mediated Na reabsorption of secreted K. The effects of furosemide are different in mice fed a high-K, alkaline (HK) diet: the large-conductance Ca-activated K (BK) channel, in conjunction with the BK β4-subunit (BK-α/β4), mediates K secretion from intercalated cells (IC) of the connecting tubule and collecting ducts. The urinary alkaline load is necessary for BK-α/β4-mediated K secretion in HK diet-fed mice. However, furosemide acidifies the urine by increasing vacuolar ATPase expression and acid secretion from IC, thereby inhibiting BK-α/β4-mediated K secretion and sparing K. In mice fed a low-Na, high-K (LNaHK) diet, furosemide causes a greater increase in plasma K concentration and reduction in K excretion than in HK diet-fed mice. Micropuncture of the early distal tubule of mice fed a LNaHK diet, but not a regular or a HK diet, reveals K secretion in the thick ascending limb of Henle’s loop. The sites of action of K secretion in individuals consuming a high-K diet should be taken into account when diuretic agents known to waste K with low or moderate K intakes are prescribed.

scholarly journals Regulation of BK-α expression in the distal nephron by aldosterone and urine pH

2013 ◽  
Vol 305 (4) ◽  
pp. F463-F476 ◽  
Author(s):  
Donghai Wen ◽  
Ryan J. Cornelius ◽  
Yang Yuan ◽  
Steven C. Sansom
Keyword(s):  
Western Blot ◽  
Immunohistochemical Analysis ◽  
Bk Channel ◽  
Distal Nephron ◽  
Membrane Expression ◽  
Urine Ph ◽  
High K ◽  
K Secretion ◽  
Acid Base Status ◽  
Apical Localization

In the distal nephron, the large-conductance Ca-activated K (BK) channel, comprised of a pore-forming-α (BK-α) and the BK-β4 subunit, promotes K excretion when mice are maintained on a high-K alkaline diet (HK-alk). We examined whether BK-β4 and the acid-base status regulate apical membrane expression of BK-α in the cortical (CCD) and medullary collecting ducts (MCD) using immunohistochemical analysis (IHC) and Western blot. With the use of IHC, BK-α of mice on acontrol diet localized mostly cytoplasmically in intercalated cells (IC) of the CCD and in the perinuclear region of both principle cells (PC) and IC of the MCD. HK-alk wild-type mice (WT), but not BK-β4 knockout mice (β4KO), exhibited increased apical BK-α in both the CCD and MCD. When given a high-K acidic diet (HK-Cl), BK-α expression increased but remained cytoplasmic in the CCD and perinuclear in the MCD of both WT and β4KO. Western blot confirmed that total BK-α expression was enhanced by either HK-alk or HK-Cl but only increased in the plasma membrane with HK-alk. Compared with controls, mice drinking NaHCO3 water exhibited more apical BK-α and total cellular BK-β4. Spironolactone given to mice on HK-alk significantly reduced K secretion and decreased total cellular BK-α but did not affect cellular BK-β4 and apical BK-α. Experiments with MDCK-C11 cells indicated that BK-β4 stabilizes surface BK-α by inhibiting degradation through a lysosomal pathway. These data suggest that aldosterone mediates a high-K-induced increase in BK-α and urinary alkalinization increases BK-β4 expression, which promotes the apical localization of BK-α.

scholarly journals K+ secretion in the rat kidney: Na+ channel-dependent and -independent mechanisms

2009 ◽  
Vol 297 (2) ◽  
pp. F389-F396 ◽  
Author(s):  
Gustavo Frindt ◽  
Lawrence G. Palmer
Keyword(s):  
Rat Kidney ◽  
Na Channel ◽  
Channel Activity ◽  
Distal Nephron ◽  
High K ◽  
Independent Mechanism ◽  
K Secretion ◽  
Channel Dependent ◽  
Excretion Rates ◽  
Dependent Pathway

Renal Na+ and K+ excretion was measured in rats with varying dietary K+ intake. The requirement for channel-mediated distal nephron Na+ reabsorption was assessed by infusing the animals with the K+-sparing diuretic amiloride via osmotic minipumps. At infusion rates of 2 nmol/min, the concentration of amiloride in the urine was 38 μM, corresponding to concentrations of 9–23 μM in the distal tubular fluid, sufficient to block >98% of Na+ transport through apical Na+ channels (ENaC). With a control K+ intake (0.6% KCl), amiloride reduced K+ excretion rates (UKV) from 0.85 ± 0.15 to 0.05 ± 0.01 μmol/min during the first 2 h of infusion, suggesting that distal nephron K+ secretion was completely dependent on the activity of Na+ channels. When K+ intake was increased by feeding overnight with a diet containing 10% KCl, amiloride reduced UKV from 7.5 ± 0.7 to 1.3 ± 0.1 μmol/min despite an increased plasma K+ of 9 mM, again suggesting a major but not exclusive role for the Na+ channel-dependent pathway of K+ secretion. The maximal measured rates of amiloride-sensitive K+ excretion correspond well with estimates based on apical K+ channel activity in distal nephron segments. However, when the animals were adapted to the high-K+ diet for 7–9 days, the diuretic decreased UKV less, from 6.1 ± 0.6 to 3.0 ± 0.8 μmol/min, indicating an increasing fraction of K+ excretion that was independent of Na+ channels. This indicates the upregulation of a Na+ channel-independent mechanism for secreting K+.

Axial heterogeneity of potassium transport across hamster thick ascending limb of Henle's loop

1994 ◽  
Vol 267 (1) ◽  
pp. F121-F129 ◽  
Author(s):  
S. Tsuruoka ◽  
C. Koseki ◽  
S. Muto ◽  
K. Tabei ◽  
M. Imai
Keyword(s):  
Electrophysiological Study ◽  
Thick Ascending Limb ◽  
Electron Microscopic ◽  
Medullary Thick Ascending Limb ◽  
Henle's Loop ◽  
Transmission Electron ◽  
K Secretion ◽  
K Concentration ◽  
K Transport

Functional significance of morphological heterogeneities along the thick ascending limb of Henle's loop of hamsters was explored by the in vitro microperfusion technique with special reference to K+ transport. The transmission electron microscopic study confirmed that there are two types of cells, with smooth surface (S-cell) and rough surface (R-cell), respectively, and that the former is abundant in the medullary thick ascending limb (MTAL), whereas the latter is in the cortical portion (CTAL). The electrophysiological study revealed that in both segments there are two cell populations, one having high basolateral and low apical membrane K+ conductances (HBC) and the other having low basolateral and high apical K+ conductances (LBC). Random cell puncture revealed that the ratios of HBC/LBC were 24/7 (77%/23%) in the MTAL and 7/22 (24%/76%) in the CTAL, suggesting that HBC corresponds to S-cell, whereas LBC corresponds to R-cell. Net K+ transport was determined in two segments by measuring K+ concentration in the collected and perfused fluid by ultramicroflame photometry. In all six tubules of MTAL, net K+ flux had a direction to reabsorption with a mean of 4.87 +/- 0.46 pmol.min-1.mm-1. In marked contrast, in all six tubules of CTAL, we observed K+ secretion with a mean of -3.81 +/- 0.49 pmol.min-1.mm-1. The transmural voltage was positive in both segments and was significantly higher in the CTAL (7.8 +/- 0.5 mV) than in the MTAL (2.5 +/- 0.2 mV). From these observations, we conclude that the S-cell corresponding to the HBC cell reabsorbs K+, whereas the R-cell corresponding to the LBC cell secrets K+.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Bicarbonate promotes BK-α/β4-mediated K excretion in the renal distal nephron

2012 ◽  
Vol 303 (11) ◽  
pp. F1563-F1571 ◽  
Author(s):  
Ryan J. Cornelius ◽  
Donghai Wen ◽  
Lori I. Hatcher ◽  
Steven C. Sansom
Keyword(s):  
Immunohistochemical Analysis ◽  
Compensatory Mechanism ◽  
Intercalated Cells ◽  
Wild Type ◽  
Distal Nephron ◽  
Acid Base ◽  
Urinary Ph ◽  
High K ◽  
K Secretion ◽  
K Concentration

Ca-activated K channels (BK), which are stimulated by high distal nephron flow, are utilized during high-K conditions to remove excess K. Because BK predominantly reside with BK-β4 in acid/base-transporting intercalated cells (IC), we determined whether BK-β4 knockout mice (β4KO) exhibit deficient K excretion when consuming a high-K alkaline diet (HK-alk) vs. high-K chloride diet (HK-Cl). When wild type (WT) were placed on HK-alk, but not HK-Cl, renal BK-β4 expression increased (Western blot). When WT and β4KO were placed on HK-Cl, plasma K concentration ([K]) was elevated compared with control K diets; however, K excretion was not different between WT and β4KO. When HK-alk was consumed, the plasma [K] was lower and K clearance was greater in WT compared with β4KO. The urine was alkaline in mice on HK-alk; however, urinary pH was not different between WT and β4KO. Immunohistochemical analysis of pendrin and V-ATPase revealed the same increases in β-IC, comparing WT and β4KO on HK-alk. We found an amiloride-sensitive reduction in Na excretion in β4KO, compared with WT, on HK-alk, indicating enhanced Na reabsorption as a compensatory mechanism to secrete K. Treating mice with an alkaline, Na-deficient, high-K diet (LNaHK) to minimize Na reabsorption exaggerated the defective K handling of β4KO. When WT on LNaHK were given NH4Cl in the drinking water, K excretion was reduced to the magnitude of β4KO on LNaHK. These results show that WT, but not β4KO, efficiently excretes K on HK-alk but not on HK-Cl and suggest that BK-α/β4-mediated K secretion is promoted by bicarbonaturia.

Abstract 040: Upregulation Of Cyp Epoxygenase In The Connecting Tubule(cnt)/cortical Collecting Duct (ccd) Is Essential For High Potassium (k) Intake-induced Antihypertensive Effect

2013 ◽  
Vol 113 (suppl_1) ◽  
Author(s):  
Daohong Lin ◽  
Chengbiao Zhang ◽  
Lijun Wang ◽  
Wenhui Wang
Keyword(s):  
Antihypertensive Effect ◽  
Salt Intake ◽  
Collecting Duct ◽  
Smooth Muscles ◽  
High Salt ◽  
Conditional Knockout ◽  
Na Channel ◽  
Thick Ascending Limb ◽  
High K ◽  
High Salt Intake

Cyp epoxygenase is responsible for metabolizing arachidonic acid to epoxyeicosatrienoic acid (EET) in the kidney and vascular tissues. EET has been shown to cause vasodilation by stimulating Ca 2+ -activated K channels in vascular smooth muscles and to have natriuretic effect by inhibiting the epithelial Na channel (ENaC) in the kidney. In the present study we used real time PCR technique to examine the effect of high salt intake or high K intake on Cyp2c44 (a major type of Cyp epoxygenase in the mouse kidney) in the proximal tubule (PxT), thick ascending limb (TAL), distal convoluted tubule (DCT) and the CNT/CCD. An increase in dietary Na content stimulates the expression of Cyp2c4 in TAL, DCT and CNT/CCD but not in PxT while an increase in dietary K intake augments the expression of Cyp2c44 only in DCT and CNT/CCD. Neither high salt intake nor high K intake has a significant effect on the blood pressure (BP) in wt mice. However, high K intake increased BP in CNT/CCD specific conditional knockout (KO) mice. In contrast, the high Na intake did not significantly increase the BP in those KO mice. This suggests that Cyp2c44 in the CNT/CCD plays a key role in preventing hypertension induced by increasing dietary K intake. Administration of amiloride (a ENaC inhibitor) restored the normal BP in KO mice fed high K diet, suggesting that down-regulation of Cyp2c44 may enhance the Na absorption in the CNT/CCD. This notion was also supported by metabolic cage study demonstrating that renal Na excretion was compromised in KO mice. We conclude that Cyp2c44 plays a key role in stimulating renal Na excretion during increasing dietary K intake and that Cyp-epoxygenase is required for antihypertensive effect induced by high K intake.

scholarly journals Effects of High Potassium and Low Temperature on the Growth and Magnesium Nutrition of Different Tomato Cultivars

HortScience ◽  
2018 ◽  
Vol 53 (5) ◽  
pp. 710-714 ◽  
Author(s):  
Huixia Li ◽  
Zhujun Chen ◽  
Ting Zhou ◽  
Yan Liu ◽  
Sajjad Raza ◽  
...  
Keyword(s):  
Low Temperature ◽  
Shoot Biomass ◽  
Total Biomass ◽  
High Potassium ◽  
Hydroponic Experiment ◽  
Root Shoot Ratio ◽  
High K ◽  
Significant Difference ◽  
Tomato Cultivars ◽  
K Concentration

The interaction between potassium (K) and magnesium (Mg) in plants has been intensively studied. However, the responses of different tomato (Solanum lycopersicum L.) cultivars to high K levels at low temperatures remained unclear. Herein, a complete randomized hydroponic experiment was conducted to evaluate the effects of temperature (25 °C day/18 °C night vs. 15 °C day/8 °C night) and K concentrations (156 mg·L−1 vs. 468 mg·L−1) on the growth and Mg nutrition of tomato cultivars Gailiangmaofen (MF) and Jinpeng No. 1 (JP). Compared with the control temperature (25 °C day/18 °C night), the low temperature decreased total biomass, shoot biomass, and Mg uptake in shoot by 17.3%, 24.1%, and 11.8%, respectively; however, the root/shoot ratio was increased. High K had no significant effect on plant growth or biomass compared with the control K concentration (156 mg·L−1); however, Mg concentrations and uptake in shoot were significantly lower under high-K treatment. Significant difference was observed for K uptake, but not for Mg uptake, between the two cultivars. There was no significant interaction between temperature and high K on Mg uptake of tomato, so a combined stress of low temperature and high K further inhibited Mg uptake and transport. Low temperature and high K increased the risk of Mg deficiency in tomato.

scholarly journals Regulation of renal Na transporters in response to dietary K

2018 ◽  
Vol 315 (4) ◽  
pp. F1032-F1041 ◽  
Author(s):  
Lei Yang ◽  
Shuhua Xu ◽  
Xiaoyun Guo ◽  
Shinichi Uchida ◽  
Alan M. Weinstein ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Time Course ◽  
Na Channel ◽  
Thick Ascending Limb ◽  
Protein Levels ◽  
Phosphorylated Form ◽  
High K ◽  
Enhanced Expression ◽  
Males And Females ◽  
Epithelial Na Channel

Changes in the expression of Na transport proteins were measured in the kidneys of mice with increased dietary K intake for 1 wk. The epithelial Na channel (ENaC) was upregulated, with enhanced expression of full-length and cleaved forms of α-ENaC and cleaved γ-ENaC. At the same time, the amount of the NaCl cotransporter NCC and its phosphorylated form decreased by ~50% and ~80%, respectively. The expression of the phosphorylated form of the Na-K-2Cl cotransporter NKCC2 also decreased, despite an increase in overall protein content. The effect was stronger in males (80%) than in females (40%). This implies that less Na+ is reabsorbed in the thick ascending limb of Henle’s loop and distal convoluted tubule along with Cl−, whereas more is reabsorbed in the aldosterone-sensitive distal nephron in exchange for secreted K+. The abundance of the proximal tubule Na/H exchanger NHE3 decreased by ~40%, with similar effects in males and females. Time-course studies indicated that NCC and NHE3 proteins decreased progressively over 7 days on a high-K diet. Expression of mRNA encoding these proteins increased, implying that the decreased protein levels resulted from decreased rates of synthesis or increased rates of degradation. The potential importance of changes in NHE3, NKCC2, and NCC in promoting K+ excretion was assessed with a mathematical model. Simulations indicated that decreased NHE3 produced the largest effect. Regulation of proximal tubule Na+ transport may play a significant role in achieving K homeostasis.

Identification and localization of BK-β subunits in the distal nephron of the mouse kidney

2007 ◽  
Vol 293 (1) ◽  
pp. F350-F359 ◽  
Author(s):  
P. Richard Grimm ◽  
Ruth M. Foutz ◽  
Robert Brenner ◽  
Steven C. Sansom
Keyword(s):  
Immunohistochemical Staining ◽  
Bk Channels ◽  
Mouse Kidney ◽  
Thick Ascending Limb ◽  
Distal Nephron ◽  
Rt Pcr ◽  
Western Blots ◽  
Nephron Segments ◽  
High K ◽  
Specific Localization

Large-conductance, Ca2+-activated K+ channels (BK), comprised of pore-forming α- and accessory β-subunits, secrete K+ in the distal nephron under high-flow and high-K+ diet conditions. BK channels are detected by electrophysiology in many nephron segments; however, the accessory β-subunit associated with these channels has not been determined. We performed RT-PCR, Western blotting, and immunohistochemical staining to determine whether BK-β1 is localized to the connecting tubule's principal-like cells (CNT) or intercalated cells (ICs), and whether BK-β2-4 are present in other distal nephron segments. RT-PCR and Western blots revealed that the mouse kidney expresses BK-β1, BK-β2, and BK-β4. Available antibodies in conjunction with BK-β1−/− and BK-β4−/− mice allowed the specific localization of BK-β1 and BK-β4 in distal nephron segments. Immunohistochemical staining showed that BK-β1 is localized in the CNT but not ICs of the connecting tubule. The localization of BK-β4 was discerned using an anti-BK-β4 antibody on wild-type tissue and anti-GFP on GFP-replaced BK-β4 mouse (BK-β4−/−) tissue. Both antibodies (anti-BK-β4 and anti-GFP) localized BK-β4 to the thick ascending limb (TAL), distal convoluted tubule (DCT), and ICs of the distal nephron. It is concluded that BK-β1 is narrowly confined to the apical membrane of CNTs in the mouse, whereas BK-β4 is expressed in the TAL, DCT, and ICs.

scholarly journals Differential regulation of ROMK (Kir1.1) in distal nephron segments by dietary potassium

2011 ◽  
Vol 300 (6) ◽  
pp. F1385-F1393 ◽  
Author(s):  
James B. Wade ◽  
Liang Fang ◽  
Richard A. Coleman ◽  
Jie Liu ◽  
P. Richard Grimm ◽  
...  
Keyword(s):  
Apical Membrane ◽  
Collecting Duct ◽  
Differential Regulation ◽  
Regulatory Mechanisms ◽  
Cortical Collecting Duct ◽  
Distal Nephron ◽  
High K ◽  
Dietary Potassium ◽  
Intracellular Compartments ◽  
K Secretion

ROMK channels are well-known to play a central role in renal K secretion, but the absence of highly specific and avid-ROMK antibodies has presented significant roadblocks toward mapping the extent of expression along the entire distal nephron and determining whether surface density of these channels is regulated in response to physiological stimuli. Here, we prepared new ROMK antibodies verified to be highly specific, using ROMK knockout mice as a control. Characterization with segmental markers revealed a more extensive pattern of ROMK expression along the entire distal nephron than previously thought, localizing to distal convoluted tubule regions, DCT1 and DCT2; the connecting tubule (CNT); and cortical collecting duct (CD). ROMK was diffusely distributed in intracellular compartments and at the apical membrane of each tubular region. Apical labeling was significantly increased by high-K diet in DCT2, CNT1, CNT2, and CD ( P < 0.05) but not in DCT1. Consistent with the large increase in apical ROMK, dramatically increased mature glycosylation was observed following dietary potassium augmentation. We conclude 1) our new antibody provides a unique tool to characterize ROMK channel localization and expression and 2) high-K diet causes a large increase in apical expression of ROMK in DCT2, CNT, and CD but not in DCT1, indicating that different regulatory mechanisms are involved in K diet-regulated ROMK channel functions in the distal nephron.

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