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 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 Acute effects of aldosterone on the epithelial Na channel in rat kidney

2015 ◽  
Vol 308 (6) ◽  
pp. F572-F578 ◽  
Author(s):  
Gustavo Frindt ◽  
Lawrence G. Palmer
Keyword(s):  
Rat Kidney ◽  
Surface Protein ◽  
Early Response ◽  
Surface Expression ◽  
Na Channel ◽  
Channel Activity ◽  
Acute Effects ◽  
Chronic Stimulation ◽  
Epithelial Na Channels ◽  
Epithelial Na Channel

The acute effects of aldosterone administration on epithelial Na channels (ENaC) in rat kidney were examined using electrophysiology and immunodetection. Animals received a single injection of aldosterone (20 μg/kg body wt), which reduced Na excretion over the next 3 h. Channel activity was assessed in principal cells of cortical collecting ducts as amiloride-sensitive whole cell clamp current ( INa). INa averaged 100 pA/cell, 20–30% of that reported for the same preparation under conditions of chronic stimulation. INa was negligible in control animals that did not receive hormone. The acute physiological response correlated with changes in ENaC processing and trafficking. These effects included increases in the cleaved forms of α-ENaC and γ-ENaC, assessed by Western blot, and increases in the surface expression of β-ENaC and γ-ENaC measured after surface protein biotinylation. These changes were qualitatively and quantitatively similar to those of chronic stimulation. This suggests that altered trafficking to or from the apical membrane is an early response to the hormone and that later increases in channel activity require stimulation of channels residing at the surface.

Effects of prostaglandin E2 on amiloride-blockable Na+ channels in a distal nephron cell line (A6)

1994 ◽  
Vol 267 (5) ◽  
pp. C1414-C1425 ◽  
Author(s):  
K. E. Kokko ◽  
P. S. Matsumoto ◽  
B. N. Ling ◽  
D. C. Eaton
Keyword(s):  
Prostaglandin E2 ◽  
Apical Cell ◽  
Na Channel ◽  
Na Channels ◽  
Channel Activity ◽  
Distal Nephron ◽  
Open Probability ◽  
A6 Cells ◽  
Channel Inhibition ◽  
Camp Levels

We studied the mechanisms by which prostaglandin E2 (PGE2) regulates amiloride-blockable 4-pS Na+ channels in A6 distal nephron cells. With each apical cell-attached patch acting as its own control, acute (3-6 min) basolateral, but not apical, exposure to 1 microM PGE2 inhibited Na+ channel activity by decreasing the open probability (Po). This PGE2-induced inhibition was attenuated by 30 min pretreatment with the protein kinase C (PKC) antagonists 1 microM staurosporine or 100 microM D-sphingosine but was insensitive to pertussis toxin (PTX). Furthermore, the time course for channel inhibition by acute PGE2 correlated with a transient increase in intracellular inositol 1,4,5-trisphosphate (IP3) levels. In contrast, after chronic (10-50 min) exposure of A6 cells to 1 microM basolateral PGE2, channel activity was stimulated compared with controls. This stimulation was due to an increase in the number of apical Na+ channels, similar to the effect of maneuvers that increase intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels in A6 cells (22). Indeed, chronic exposure to basolateral PGE2 correlated with a sustained increase in cAMP levels. In conclusion, 1) the regulation of apical 4-pS highly selective Na+ channel activity by basolateral PGE2 is a complicated biphasic process, which includes inhibition by acute PGE2 and stimulation by chronic PGE2 exposure; 2) acute PGE2 promotes a transient generation of IP3 which activates Ca(2+)-dependent PKC and promotes a decrease in Po; 3) chronic PGE2 promotes a sustained generation of cAMP that leads to an increase in channel density; and 4) both the acute and chronic effects of PGE2 on Na+ channels are PTX-insensitive processes.

Regulation of amiloride-sensitive Na+ channels by endothelin-1 in distal nephron cells

1996 ◽  
Vol 271 (2) ◽  
pp. F451-F460 ◽  
Author(s):  
M. S. Gallego ◽  
B. N. Ling
Keyword(s):  
Na Channel ◽  
Na Channels ◽  
Channel Activity ◽  
Distal Nephron ◽  
Endothelin 1 ◽  
Channel Inhibition ◽  
Current Voltage ◽  
Mean Time ◽  
Current Voltage Relationship

We used patch-clamp methods to investigate the effects of basolateral endothelin-1 (ET-1) on the amiloride-sensitive Na+ channel in A6 distal nephron cells. One hundred picomolar ET-1 decreased channel activity via an increase in mean time closed (P < 0.01, n = 10). Channel inhibition by pM ET-1 was mimicked by an ET-B receptor agonist (P < 0.05, n = 7) and was prevented by ET-B antagonists (P = 0.14, n = 10) but not by an ET-A antagonist (P < 0.05, n = 4). With the inhibitory ET-B receptor blocked, higher doses of ET-1 (10 nM) actually increased channel activity through an increase in mean time open (P < 0.001, n = 12). The current-voltage relationship and the number of channels were not changed by basolateral ET-1 exposure. We conclude that 1) basolateral ET-1 regulates amiloride-sensitive Na+ channels; 2) binding of picomolar ET-1 to ET-B receptors inhibits, whereas the binding of nanomolar ET-1 to a different ET receptor (likely ET-A) stimulates, channel activity; and 3) these dose-dependent, distal nephron responses provide a potential mechanism for the in vivo natriuresis and antinatriuresis observed in response to "subpressor" and "pressor" concentrations of ET-1, respectively.

Regulation of maturation and processing of ENaC subunits in the rat kidney

2006 ◽  
Vol 291 (3) ◽  
pp. F683-F693 ◽  
Author(s):  
Zuhal Ergonul ◽  
Gustavo Frindt ◽  
Lawrence G. Palmer
Keyword(s):  
Collecting Duct ◽  
Rat Kidney ◽  
Na Channel ◽  
Cortical Collecting Duct ◽  
Α Subunit ◽  
Salt Restriction ◽  
High K ◽  
Electrophysiological Measurements ◽  
Immature Form ◽  
Epithelial Na Channel

Antibodies directed against subunits of the epithelial Na channel (ENaC) were used together with electrophysiological measurements in the cortical collecting duct to investigate the processing of the proteins in rat kidney with changes in Na or K intake. When animals were maintained on a low-Na diet for 7–9 days, the abundance of two forms of the α-subunit, with apparent masses of 85 and 30 kDa, increased. Salt restriction also increased the abundance of the β-subunit and produced an endoglycosidase H (Endo H)-resistant pool of this subunit. The abundance of the 90-kDa form of the γ-subunit decreased, whereas that of a 70-kDa form increased and this peptide also exhibited Endo H-resistant glycosylation. These changes in α- and γ-subunits were correlated with increases in Na conductance elicited by a 4-h infusion with aldosterone. Changes in all three subunits were correlated with decreases in Na conductance when Na-deprived animals drank saline for 5 h. We conclude that ENaC subunits are mainly in an immature form in salt-replete rats. With Na depletion, the subunits mature in a process that involves proteolytic cleavage and further glycosylation. Similar changes occurred in α- and γ- but not β-subunits when animals were treated with exogenous aldosterone, and in β- and γ- but not α-subunits when animals were fed a high-K diet. Changes in the processing and maturation of the channels occur rapidly enough to be involved in the daily regulation of ENaC activity and Na reabsorption by the kidney.

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 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 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.

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.

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