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.

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 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 Furosemide reduces BK-αβ4-mediated K+ secretion in mice on an alkaline high-K+ diet

2019 ◽  
Vol 316 (2) ◽  
pp. F341-F350 ◽  
Author(s):  
Bangchen Wang ◽  
Jun Wang-France ◽  
Huaqing Li ◽  
Steven C. Sansom
Keyword(s):  
Plasma Aldosterone ◽  
Elevated Plasma ◽  
Wild Type ◽  
Distal Nephron ◽  
Urine Ph ◽  
Alkaline Urine ◽  
High K ◽  
K Secretion ◽  
Cardioprotective Effects ◽  
Apical Localization

Special high-K diets have cardioprotective effects and are often warranted in conjunction with diuretics such as furosemide for treating hypertension. However, it is not understood how a high-K diet (HK) influences the actions of diuretics on renal K+ handling. 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. We previously found that an alkaline urine is required for large conductance Ca2+-activated K+ (BK)-αβ4-mediated K+ secretion in mice on HK. We therefore hypothesized that furosemide could reduce BK-αβ4-mediated K+ secretion by acidifying the urine. Treating with furosemide (drinking water) for 11 days led to decreased urine pH in both wild-type (WT) and BK-β4-knockout mice (BK-β4-KO) with increased V-ATPase expression and elevated plasma aldosterone levels. However, furosemide decreased renal K+ clearance and elevated plasma [K+] in WT but not BK-β4-KO. Western blotting and immunofluorescence staining showed that furosemide treatment decreased cortical expression of BK-β4 and reduced apical localization of BK-α in connecting tubules. Addition of the carbonic anhydrase inhibitor, acetazolamide, to furosemide water restored urine pH along with renal K+ clearance and plasma [K+] to control levels. Acetazolamide plus furosemide also restored the cortical expression of BK-β4 and BK-α in connecting tubules. These results indicate that in mice adapted to HK, furosemide reduces BK-αβ4-mediated K+ secretion by acidifying the urine.

scholarly journals ENaC and ROMK activity are inhibited in the DCT2/CNT of TgWnk4PHAII mice

2017 ◽  
Vol 312 (4) ◽  
pp. F682-F688 ◽  
Author(s):  
Chengbiao Zhang ◽  
Lijun Wang ◽  
Xiao-Tong Su ◽  
Junhui Zhang ◽  
Dao-Hong Lin ◽  
...  
Keyword(s):  
Patch Clamp ◽  
Type Ii ◽  
Channel Activity ◽  
Wild Type ◽  
Distal Nephron ◽  
High K ◽  
Pseudohypoaldosteronism Type Ii ◽  
Nephron Segment ◽  
Pseudohypoaldosteronism Type ◽  
Stimulation Of

Mice transgenic for genomic segments harboring PHAII (pseudohypoaldosteronism type II) mutant Wnk4 (with-No-Lysine kinase 4) (TgWnk4PHAII) have hyperkalemia which is currently believed to be the result of high activity of Na-Cl cotransporter (NCC). This leads to decreasing Na+ delivery to the distal nephron segment including late distal convoluted tubule (DCT) and connecting tubule (CNT). Since epithelial Na+ channel (ENaC) and renal outer medullary K+ channel (ROMK or Kir4.1) are expressed in the late DCT and play an important role in mediating K+ secretion, the aim of the present study is to test whether ROMK and ENaC activity in the DCT/CNT are also compromised in the mice expressing PHAII mutant Wnk4. Western blot analysis shows that the expression of βENaC and γENaC subunits but not αENaC subunit was lower in TgWnk4PHAII mice than that in wild-type (WT) and TgWnk4WT mice. Patch-clamp experiments detected amiloride-sensitive Na+ currents and TPNQ-sensitive K+ currents in DCT2/CNT, suggesting the activity of ENaC and ROMK. However, both Na+ and ROMK currents in DCT2/CNT of TgWnk4PHAII mice were significantly smaller than those in WT and TgWnk4WT mice. In contrast, the basolateral K+ currents in the DCT were similar among three groups, despite higher NCC expression in TgWnk4PHAII mice than those of WT and TgWnk4WTmice. An increase in dietary K+ intake significantly increased both ENaC and ROMK currents in the DCT2/CNT of all three groups. However, high-K+ (HK) intake-induced stimulation of Na+ and K+ currents was smaller in TgWnk4PHAII mice than those in WT and TgWnk4WT mice. We conclude that ENaC and ROMK channel activity in DCT2/CNT are inhibited in TgWnk4PHAII mice and that Wnk4PHAII-induced inhibition of ENaC and ROMK may contribute to the suppression of K+ secretion in the DCT2/CNT in addition to increased NCC activity.

scholarly journals Carbonic anhydrase 2 deficiency leads to increased pyelonephritis susceptibility

2014 ◽  
Vol 307 (7) ◽  
pp. F869-F880 ◽  
Author(s):  
David S. Hains ◽  
Xi Chen ◽  
Vijay Saxena ◽  
Evan Barr-Beare ◽  
Weisi Flemming ◽  
...  
Keyword(s):  
Carbonic Anhydrase ◽  
Intercalated Cells ◽  
Bacterial Clearance ◽  
Wild Type ◽  
Acid Base ◽  
Wild Type Littermate ◽  
Innate Defense ◽  
Bacterial Response ◽  
Infection Susceptibility ◽  
Acid Base Status

Carbonic anhydrase 2 regulates acid-base homeostasis, and recent findings have indicated a correlation between cellular control of acid-base status and the innate defense of the kidney. Mice deficient in carbonic anhydrase 2 ( Car2−/− mice) have metabolic acidosis, impaired urine acidification, and are deficient in normal intercalated cells. The objective of the present study was to evaluate the biological consequences of carbonic anhydrase 2 deficiency in a murine model of pyelonephritis. Infection susceptibility and transcription of bacterial response components in Car2−/− mice were compared with wild-type littermate controls. Car2−/− mice had increased kidney bacterial burdens along with decreased renal bacterial clearance after inoculation compared with wild-type mice. Standardization of the urine pH and serum HCO3− levels did not substantially alter kidney infection susceptibility between wild-type and Car2−/− mice; thus, factors other than acid-base status are responsible. Car2−/− mice had significantly increased neutrophil-gelatinase-associated lipocalin mRNA and protein and expression at baseline and a marked decreased ability to upregulate key bacterial response genes during pyelonephritis. Our findings provide in vivo evidence that supports a role for carbonic anhydrase 2 and intercalated cells in promoting renal bacterial clearance. Decreased carbonic anhydrase expression results in increased antimicrobial peptide production by cells other than renal intercalated cells, which is not sufficient to prevent infection after a bacterial challenge.

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+.

scholarly journals Coupled ATP and potassium efflux from intercalated cells

2011 ◽  
Vol 300 (6) ◽  
pp. F1319-F1326 ◽  
Author(s):  
J. David Holtzclaw ◽  
Ryan J. Cornelius ◽  
Lori I. Hatcher ◽  
Steven C. Sansom
Keyword(s):  
Purinergic Signaling ◽  
Atp Release ◽  
K Channel ◽  
Intercalated Cells ◽  
Wild Type ◽  
Potassium Efflux ◽  
Atp Secretion ◽  
K Secretion ◽  
Si Rna ◽  
Volume Decrease

Increased flow in the distal nephron induces K secretion through the large-conductance, calcium-activated K channel (BK), which is primarily expressed in intercalated cells (IC). Since flow also increases ATP release from IC, we hypothesized that purinergic signaling has a role in shear stress (τ; 10 dynes/cm2) -induced, BK-dependent, K efflux. We found that 10 μM ATP led to increased IC Ca concentration, which was significantly reduced in the presence of the P2 receptor blocker suramin or calcium-free buffer. ATP also produced BK-dependent K efflux, and IC volume decrease. Suramin inhibited τ-induced K efflux, suggesting that K efflux is at least partially dependent on purinergic signaling. BK-β4 small interfering (si) RNA, but not nontarget siRNA, decreased ATP secretion and both ATP-dependent and τ-induced K efflux. Similarly, carbenoxolone (25 μM), which blocks connexins, putative ATP pathways, blocked τ-induced K efflux and ATP secretion. Compared with BK-β4−/− mice, wild-type mice with high distal flows exhibited significantly more urinary ATP excretion. These data demonstrate coupled electrochemical efflux between K and ATP as part of the mechanism for τ-induced ATP release in IC.

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.

Renal potassium transport: morphological and functional adaptations

1989 ◽  
Vol 257 (5) ◽  
pp. R989-R997 ◽  
Author(s):  
B. A. Stanton
Keyword(s):  
Collecting Duct ◽  
Cell Structure ◽  
Basolateral Membrane ◽  
Distal Tubule ◽  
Morphological Evidence ◽  
Intercalated Cells ◽  
Principal Cells ◽  
K Secretion ◽  
K Concentration ◽  
And Function

Maintenance of K+ homeostasis in mammals and amphibians depends primarily on the kidneys which excrete 95% of K+ ingested in the diet. The amount of K+ in the urine is determined by the rate of K+ secretion or absorption by the distal tubule and the collecting duct. When K+ intake is increased, K+ secretion rises. The mechanisms of K+ secretion by the distal tubule and collecting duct are so efficient that K+ intake can increase 20-fold with little or no increase in body K+ content or in plasma K+ concentration. Elevated K+ secretion by the distal tubule and collecting duct occurs in part because of an increase in the quantity of Na+-K+-adenosinetriphosphatase (Na+-K+-ATPase) and amplification of the basolateral membrane of principal cells. When dietary K+ intake is reduced, urinary K+ excretion falls, because K+ secretory mechanisms are suppressed and K+ absorptive mechanisms, residing in the distal tubule and collecting duct, are activated. Because a low-K+ diet is associated with hypertrophy of intercalated cells, it has been suggested that this cell type absorbs K+, possibly by an H+-K+-ATPase. In this review, I discuss the functional and morphological evidence that supports the view that principal cells secrete K+ and that intercalated cells absorb K+. In addition, some of the hormones and factors that are responsible for these changes in cell structure and function are discussed.

Increased expression of H+-ATPase in inner medullary collecting duct of aquaporin-1-deficient mice

2003 ◽  
Vol 285 (3) ◽  
pp. F550-F557 ◽  
Author(s):  
Young-Hee Kim ◽  
Jin Kim ◽  
A. S. Verkman ◽  
Kirsten M. Madsen
Keyword(s):  
Kidney Development ◽  
De Novo ◽  
Collecting Duct ◽  
Apical Plasma Membrane ◽  
Intercalated Cells ◽  
Wild Type ◽  
Urinary Ph ◽  
Aquaporin 1 ◽  
Inner Medullary Collecting Duct ◽  
Medullary Collecting Duct

Phenotype analysis has demonstrated that aquaporin-1 (AQP1) null mice are polyuric and manifest a urinary concentrating defect because of an inability to create a hypertonic medullary interstitium. We report here that deletion of AQP1 is also associated with a decrease in urinary pH from 6.15 ± (SE) 0.1 to 5.63 ± 0.07. To explore the mechanism of the decrease in urinary pH, we examined the expression of H+-ATPase in kidneys of AQP1 null mice. There was strong labeling for H+-ATPase in intercalated cells and proximal tubule cells in both AQP1 null and wild-type mice. Strong H+-ATPase immunostaining was also present in the apical plasma membrane of inner medullary collecting duct (IMCD) cells in AQP1 null mice, whereas no H+-ATPase labeling was observed in IMCD cells in wild-type mice. In addition, there was an increase in the prevalence of type A intercalated cells in the IMCD of AQP1 null mice, suggesting that the deletion of intercalated cells from the IMCD, which normally occurs during postnatal kidney development, was impaired. Western blot analysis of H+-ATPase expression in the different regions of the kidney demonstrated a significant increase in H+-ATPase protein in the inner medulla of AQP1 null mice compared with wild-type mice. There were no changes in H+-ATPase expression in the cortex or outer medulla. These results represent the first demonstration of apical H+-ATPase immunoreactivity in IMCD cells in vivo and suggest that the decrease in urinary pH observed in AQP1 null mice is due to upregulation of H+-ATPase in the IMCD. The induction of H+-ATPase expression in IMCD cells of AQP1 null mice may be related to the chronically low interstitial osmolality in these animals. The challenge will be to identify the molecular signal(s) responsible for the de novo H+-ATPase expression.

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