Intercalated cell BKα subunit is required for flow-induced K+ secretion

Kidneys play a central role in regulation of potassium homeostasis and maintenance of plasma K+ levels within a narrow physiological range. With-no-lysine (WNK) kinases, specifically WNK1 and WNK4, have been recognized to regulate K+ balance, in part, by orchestrating maxi K+ channel (BK)-dependent K+ secretion in the aldosterone-sensitive distal nephron (ASDN), which includes the connecting tubule and collecting duct. We recently demonstrated that the Ca2+-permeable TRPV4 channel is essential for BK activation in the ASDN. Furthermore, high K+ diet increases TRPV4 activity and expression largely in an aldosterone-dependent manner. In the current study, we aimed to test whether WNK kinases contribute to regulation of TRPV4 activity and its stimulation by aldosterone. Systemic inhibition of WNK with WNK463 (1 mg/kgBW for 3 days) markedly decreased TRPV4-dependent Ca2+ influx in freshly isolated split-opened collecting ducts. Aldosterone greatly increased TRPV4 activity and expression in cultured mpkCCDc14 cells and this effect was abolished in the presence of WNK463. Selective inhibition of WNK1 with WNK-in-11 (400 nM, 24 h) recapitulated the effects of WNK463 on TRPV4-dependent Ca2+ influx. Interestingly, WNK-in-11 did not interfere with up-regulation of TRPV4 expression by aldosterone, but prevented translocation of the channel to the apical plasma membrane. Furthermore, co-expression of TRPV4 and WNK1 into Chinese hamster ovary (CHO) cells increased the macroscopic TRPV4-dependent cation currents. In contrast, over-expression of TRPV4 with a dominant negative WNK1 variant (K233M) decreased the whole-cell currents, suggesting both stimulatory and permissive roles of WNK1 in regulation of TRPV4 activity. Overall, we show that WNK1 is essential for setting functional TRPV4 expression in the ASDN at the baseline and in response to aldosterone. We propose that this new mechanism contributes to regulation of K+ secretion and, by extension, urinary K+ levels to maintain systemic potassium homeostasis.

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Dibutyryl cAMP activates bumetanide-sensitive electrolyte transport in Malpighian tubules

AJP Cell Physiology ◽

10.1152/ajpcell.1991.261.3.c521 ◽

1991 ◽

Vol 261 (3) ◽

pp. C521-C529 ◽

Cited By ~ 66

Author(s):

J. L. Hegarty ◽

B. Zhang ◽

T. L. Pannabecker ◽

D. H. Petzel ◽

M. D. Baustian ◽

...

Keyword(s):

Yellow Fever ◽

Apical Membrane ◽

Basolateral Membrane ◽

Fluid Secretion ◽

Ringer Solution ◽

Malpighian Tubules ◽

Membrane Voltage ◽

Dibutyryl Camp ◽

K Secretion ◽

Transepithelial Voltage

The effects of dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP) and bumetanide (both 10(-4) M) on transepithelial Na+, K+, Cl-, and fluid secretion and on tubule electrophysiology were studied in isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti. Peritubular DBcAMP significantly increased Na+, Cl-, and fluid secretion but decreased K+ secretion. In DBcAMP-stimulated tubules, bumetanide caused Na+, Cl-, and fluid secretion to return to pre-cAMP control rates and K+ secretion to decrease further. Peritubular bumetanide significantly increased Na+ secretion and decreased K+ secretion so that Cl- and fluid secretion did not change. In bumetanide-treated tubules, the secretagogue effects of DBcAMP are blocked. In isolated Malpighian tubules perfused with symmetrical Ringer solution, DBcAMP significantly hyperpolarized the transepithelial voltage (VT) and depolarized the basolateral membrane voltage (Vbl) with no effect on apical membrane voltage (Va). Total transepithelial resistance (RT) and the fractional resistance of the basolateral membrane (fRbl) significantly decreased. Bumetanide also hyperpolarized VT and depolarized Vbl, however without significantly affecting RT and fRbl. Together these results suggest that, in addition to stimulating electroconductive transport, DBcAMP also activates a nonconductive bumetanide-sensitive transport system in Aedes Malpighian tubules.

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Intercalated cell-specific Rh B glycoprotein deletion diminishes renal ammonia excretion response to hypokalemia

AJP Renal Physiology ◽

10.1152/ajprenal.00301.2012 ◽

2013 ◽

Vol 304 (4) ◽

pp. F422-F431 ◽

Cited By ~ 20

Author(s):

Jesse M. Bishop ◽

Hyun-Wook Lee ◽

Mary E. Handlogten ◽

Ki-Hwan Han ◽

Jill W. Verlander ◽

...

Keyword(s):

Metabolic Acidosis ◽

Collecting Duct ◽

Ammonia Excretion ◽

Ammonia Concentration ◽

Intercalated Cells ◽

Cortical Collecting Duct ◽

Intercalated Cell ◽

Transporter Family ◽

Total Ammonia ◽

Normal Increase

The ammonia transporter family member, Rh B Glycoprotein (Rhbg), is an ammonia-specific transporter heavily expressed in the kidney and is necessary for the normal increase in ammonia excretion in response to metabolic acidosis. Hypokalemia is a common clinical condition in which there is increased renal ammonia excretion despite the absence of metabolic acidosis. The purpose of this study was to examine Rhbg's role in this response through the use of mice with intercalated cell-specific Rhbg deletion (IC-Rhbg-KO). Hypokalemia induced by feeding a K+-free diet increased urinary ammonia excretion significantly. In mice with intact Rhbg expression, hypokalemia increased Rhbg protein expression in intercalated cells in the cortical collecting duct (CCD) and in the outer medullary collecting duct (OMCD). Deletion of Rhbg from intercalated cells inhibited hypokalemia-induced changes in urinary total ammonia excretion significantly and completely prevented hypokalemia-induced increases in urinary ammonia concentration, but did not alter urinary pH. We conclude that hypokalemia increases Rhbg expression in intercalated cells in the cortex and outer medulla and that intercalated cell Rhbg expression is necessary for the normal increase in renal ammonia excretion in response to hypokalemia.

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Abstract 114: K+ Rich Diet During Angiotensin II Hypertension Reduces Renal Na-Cl Cotransporter and Phosphorylation, but Not Blood Pressure

Hypertension ◽

10.1161/hyp.66.suppl_1.114 ◽

2015 ◽

Vol 66 (suppl_1) ◽

Author(s):

Luciana C Veiras ◽

Jiyang Han ◽

Donna L Ralph ◽

Alicia A McDonough

Keyword(s):

Blood Pressure ◽

Urine Volume ◽

Weight Ratio ◽

Distal Tubule ◽

Reduce Blood Pressure ◽

Ang Ii ◽

Sprague Dawley ◽

Sprague Dawley Rats ◽

K Secretion ◽

Pressure Natriuresis

During Ang II hypertension distal tubule Na-Cl Cotransporter (NCC) abundance and its activating phosphorylation (NCCp), as well as Epithelial Na+ channels (ENaC) abundance and activating cleavage are increased 1.5-3 fold. Fasting plasma [K+] is significantly lower in Ang II hypertension (3.3 ± 0.1 mM) versus controls (4.0 ± 0.1 mM), likely secondary to ENaC stimulation driving K+ secretion. The aim of this study was to test the hypothesis that doubling dietary K+ intake during Ang II infusion will lower NCC and NCCp abundance to increase Na+ delivery to ENaC to drive K+ excretion and reduce blood pressure. Methods: Male Sprague Dawley rats (225-250 g; n= 7-9/group) were treated over 2 weeks: 1) Control 1% K diet fed (C1K); 2) Ang II infused (400 ng/kg/min) 1% K diet fed (A1K); or 3) Ang II infused 2% K diet fed (A2K). Blood pressure (BP) was determined by tail cuff, electrolytes by flame photometry and transporters’ abundance by immunoblot of cortical homogenates. Results: As previously reported, Ang II infusion increased systolic BP (from 132 ± 5 to 197 ± 4 mmHg), urine volume (UV, 2.4 fold), urine Na+ (UNaV, 1.3 fold), heart /body weight ratio (1.23 fold) and clearance of endogenous Li+ (CLi, measures fluid volume leaving the proximal tubule, from 0.26 ± 0.02 to 0.51 ± 0.01 ml/min/kg) all evidence for pressure natriuresis. A2K rats exhibited normal plasma [K+] (4.6 ± 0.1 mM, unfasted), doubled urine K+ (UKV, from 0.20 to 0.44 mmol/hr), and increased CLi (to 0.8 ± 0.1 ml/min/kg) but UV, UNaV, cardiac hypertrophy and BP were unchanged versus the A1K group. As expected, NCC, NCCpS71 and NCCpT53 abundance increased in the A1K group to 1.5 ± 0.1, 2.9 ± 0.5 and 2.8 ± 0.4 fold versus C1K, respectively. As predicted by our hypothesis, when dietary K+ was doubled (A2K), Ang II infusion did not activate NCC, NCCpS71 nor NCCpT53 (0.91 ± 0.04, 1.3 ± 0.1 and 1.6 ± 0.2 fold versus C1K, respectively). ENaC subunit abundance and cleavage increased 1.5 to 3 fold in both A1K and A2K groups; ROMK was unaffected by Ang II or dietary K. In conclusion, evidence is presented that stimulation of NCC during Ang II hypertension is secondary to K+ deficiency driven by ENaC stimulation since doubling dietary K+ prevents the activation. The results also indicate that elevation in BP is independent of NCC activation

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Mineralocorticoid regulation of apical cell membrane Na+ and K+ transport of the cortical collecting duct

AJP Renal Physiology ◽

10.1152/ajprenal.1985.248.6.f858 ◽

1985 ◽

Vol 248 (6) ◽

pp. F858-F868 ◽

Cited By ~ 28

Author(s):

S. C. Sansom ◽

R. G. O'Neil

Keyword(s):

Cell Membrane ◽

Tight Junction ◽

Apical Membrane ◽

Collecting Duct ◽

Apical Cell ◽

Cortical Collecting Duct ◽

Apical Cell Membrane ◽

K Secretion ◽

Junction Conductance ◽

K Transport

The effects of mineralocorticoid (DOCA) treatment of rabbits on the Na+ and K+ transport properties of the cortical collecting duct apical cell membrane were assessed using microelectrode techniques. Applying standard cable techniques and equivalent circuit analysis to the isolated perfused tubule, the apical cell membrane K+ and Na+ currents and conductances could be estimated from the selective effects of the K+ channel blocker Ba2+ and the Na+ channel blocker amiloride on the apical membrane; amiloride treatment was observed also to decrease the tight junction conductance by an average of 10%. After 1 day of DOCA treatment, the Na+ conductance and current (Na+ influx) of the apical cell membrane doubled and remained elevated with prolonged treatment for up to 2 wk. The apical cell membrane K+ conductance was not influenced after 1 day, although the K+ current (K+ secretion) increased significantly due to an increased driving force for K+ exit. After 4 days or more of DOCA treatment the K+ conductance doubled, resulting in a further modest stimulation in K+ secretion. After 2 wk of DOCA treatment the tight junction conductance decreased by near 30%, resulting in an additional hyperpolarization of the transepithelial voltage, thereby favoring K+ secretion. It is concluded that the acute effect (within 1 day) of mineralocorticoids on Na+ and K+ transport is an increase in the apical membrane Na+ conductance followed by delayed chronic alterations in the apical membrane K+ conductance and tight junction conductance, thereby resulting in a sustained increased capacity of the tubule to reabsorb Na+ and secrete K+.

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Is the Endolymphatic K Secretion Electrogenic?

Acta Oto-Laryngologica ◽

10.3109/00016489309135820 ◽

1993 ◽

Vol 113 (3) ◽

pp. 335-337 ◽

Cited By ~ 2

Author(s):

Evelyne Ferrary ◽

Christian Bernard ◽

Nicolas Julien ◽

Olivier Sterkers ◽

Claude Amiel

Keyword(s):

K Secretion

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Chloride transport by the cortical and outer medullary collecting duct

AJP Renal Physiology ◽

10.1152/ajprenal.1987.253.2.f203 ◽

1987 ◽

Vol 253 (2) ◽

pp. F203-F212 ◽

Cited By ~ 13

Author(s):

V. L. Schuster ◽

J. B. Stokes

Keyword(s):

Chloride Transport ◽

Collecting Duct ◽

Exchange Process ◽

Basolateral Membrane ◽

Fine Tuning ◽

Transport Systems ◽

Acid Base ◽

Intercalated Cell ◽

Cl Channel ◽

Collecting Tubule

The processes by which chloride is transported by the cortical and outer medullary collecting tubule have been most extensively studied using in vitro microperfusion of rabbit tubules. Chloride appears to be transported by three major mechanisms. First, Cl can be actively reabsorbed by an electroneutral Cl-HCO3 exchanger localized to the apical membrane of the HCO3-secreting (beta-type) intercalated cell. Cl exits this cell via a basolateral Cl channel. This anion exchange process can also operate in a Cl self-exchange mode, is stimulated acutely by beta-adrenergic agonists and cAMP, and is regulated chronically by in vivo acid-base status. Second, Cl can diffuse passively down electrochemical gradients via the paracellular pathway. Although this pathway does not appear to be selectively permeable to Cl, it is large enough to allow for significant passive reabsorption. Third, Cl undergoes recycling across the basolateral membrane of the H+-secreting (alpha-type) intercalated cell. HCO3 exit from this cell brings Cl into the cell via electroneutral Cl-HCO3 exchange; Cl then exits the cell via a Cl channel. Cl transport is thus required for acidification and alkalinization of the urine. Both of these processes exist in the cortical collecting tubule. Their simultaneous operation allows fine tuning of acid-base excretion. In addition, these transport systems, when functioning at equal rates, effect apparent electrogenic net Cl absorption without changing net HCO3 transport. These systems may play an important role in regulating Cl balance.

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Luminal influences on potassium secretion: chloride, sodium, and thiazide diuretics

AJP Renal Physiology ◽

10.1152/ajprenal.1992.262.6.f1076 ◽

1992 ◽

Vol 262 (6) ◽

pp. F1076-F1082 ◽

Cited By ~ 5

Author(s):

H. Velazquez ◽

D. H. Ellison ◽

F. S. Wright

Keyword(s):

Distal Tubule ◽

Distal Convoluted Tubule ◽

Thiazide Diuretics ◽

Maximal Level ◽

Luminal Membrane ◽

K Secretion ◽

Potassium Secretion

In the presence of Cl-, K+ secretion by the distal tubule saturates with increasing luminal Na+ concentration. Apparent maximal K+ secretion is attained with luminal Na+ concentrations of 40 mM. The results of the present study show that lowering the Cl- concentration of luminal fluid can increase the level of Na(+)-stimulated K+ secretion beyond the maximal level attained in the presence of Cl-. The effect of lowering luminal Cl- concentration to less than 10 mM on K+ secretion is greater with higher Na+ concentration. Under these conditions, chlorothiazide decreases K+ secretion. When chlorothiazide is present, changing the Na+ concentration does not affect K+ secretion. Because in rats a thiazide effect is attributed primarily to the distal convoluted tubule (DCT), we postulate that it is primarily DCT cells that increase K+ secretion when Na+ concentration is raised in the presence of low luminal Cl- concentration. We propose that the rat DCT cells have both an absorptive Na(+)-Cl- cotransport mechanism and a secretory K(+)-Cl- cotransport mechanism in the luminal membrane that can mediate the apparent exchange of Na+ for K+.

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