Is the Endolymphatic K Secretion Electrogenic?

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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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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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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Role of NKCC in BK channel-mediated net K+ secretion in the CCD

AJP Renal Physiology ◽

10.1152/ajprenal.00347.2011 ◽

2011 ◽

Vol 301 (5) ◽

pp. F1088-F1097 ◽

Cited By ~ 37

Author(s):

Wen Liu ◽

Carlos Schreck ◽

Richard A. Coleman ◽

James B. Wade ◽

Yubelka Hernandez ◽

...

Keyword(s):

Collecting Duct ◽

Bk Channels ◽

Bk Channel ◽

Taqman Assay ◽

Specific Cell ◽

Cortical Collecting Duct ◽

Ph Indicator ◽

Transport Pathway ◽

K Secretion

Apical SK/ROMK and BK channels mediate baseline and flow-induced K secretion (FIKS), respectively, in the cortical collecting duct (CCD). BK channels are detected in acid-base transporting intercalated (IC) and Na-absorbing principal (PC) cells. Although the density of BK channels is greater in IC than PC, Na-K-ATPase activity in IC is considered inadequate to sustain high rates of urinary K secretion. To test the hypothesis that basolateral NKCC in the CCD contributes to BK channel-mediated FIKS, we measured net K secretion ( JK) and Na absorption ( JNa) at slow (∼1) and fast (∼5 nl·min−1·mm−1) flow rates in rabbit CCDs microperfused in vitro in the absence and presence of bumetanide, an inhibitor of NKCC, added to the bath. Bumetanide inhibited FIKS but not basal JK, JNa, or the flow-induced [Ca2+]i transient necessary for BK channel activation. Addition of luminal iberiotoxin, a BK channel inhibitor, to bumetanide-treated CCDs did not further reduce JK. Basolateral Cl removal reversibly inhibited FIKS but not basal JK or JNa. Quantitative PCR performed on single CCD samples using NKCC1- and 18S-specific primers and probes and the TaqMan assay confirmed the presence of the transcript in this nephron segment. To identify the specific cell type to which basolateral NKCC is localized, we exploited the ability of NKCC to accept NH4+ at its K-binding site to monitor the rate of bumetanide-sensitive cytosolic acidification after NH4+ addition to the bath in CCDs loaded with the pH indicator dye BCECF. Both IC and PC were found to have a basolateral bumetanide-sensitive NH4+ entry step and NKCC1-specific antibodies labeled the basolateral surfaces of both cell types in CCDs. These results suggest that BK channel-mediated FIKS is dependent on a basolateral bumetanide-sensitive, Cl-dependent transport pathway, proposed to be NKCC1, in both IC and PC in the CCD.

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Unidirectional ion movements in the hindgut of larval Sarcophaga bullata (Diptera: Sarcophagidae)

Journal of Experimental Biology ◽

10.1242/jeb.64.1.89 ◽

1976 ◽

Vol 64 (1) ◽

pp. 89-100

Author(s):

R. D. Prusch

Keyword(s):

Sarcophaga Bullata ◽

K Secretion ◽

Ion Movements

1. Unidirectional Na+, K+, and Cl- fluxes were measured across the isolated hindgut of larval Sarcophaga bullata. 2. Both K+ and Cl- are actively secreted into the hindgut lumen, whereas Na+ is distributed passively. 3. The movements of K+ and Cl- are not entirely independent of each other, and the movement of one ion influences the flux of the co-ion. 4. The NH4+ ion is secreted into the hindgut by a mechanism separate from K+ secretion.

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Effect of insulin on potassium secretion in rabbit cortical collecting ducts

AJP Renal Physiology ◽

10.1152/ajprenal.1992.262.1.f30 ◽

1992 ◽

Vol 262 (1) ◽

pp. F30-F35 ◽

Cited By ~ 5

Author(s):

H. Furuya ◽

K. Tabei ◽

S. Muto ◽

Y. Asano

Keyword(s):

Collecting Duct ◽

Dependent Manner ◽

Cortical Collecting Duct ◽

Plasma Insulin Concentration ◽

Concentration Dependent Manner ◽

K Secretion ◽

Potassium Secretion ◽

Transepithelial Voltage ◽

K Transport

Insulin is known to play an important role in the regulation of extrarenal K homeostasis. Previous clearance studies have shown that insulin decreases urinary K excretion, but the responsible nephron segments have not been identified. In this microperfusion study, in vitro, the effect of insulin on K transport in the cortical collecting duct (CCD), which is thought to be an important segment for regulation of the final urinary K excretion, was investigated. Basolateral insulin (10(-6) M) significantly inhibited net K secretion by 20% (mean JK = -26.2 +/- 4.2 peq.mm-1.min-1 for controls compared with -21.1 +/- 3.4 with insulin, P less than 0.001) and depolarized the transepithelial voltage (VT, from -14.6 +/- 3.5 to -10.8 +/- 3.5 mV, P less than 0.005), recovery did not occur over 60 min. Insulin (10(-11)-10(-5) M) depressed K secretion and depolarized the VT in a concentration-dependent manner. The half-maximal concentration was 5 x 10(-10) M, which is within the physiological range of plasma insulin concentration. In tubules of deoxycorticosterone acetate-treated rabbits, insulin also produced a significant fall in K secretion (from -43.4 +/- 7.5 to -36.1 +/- 5.7 peq.mm-1.min-1, P less than 0.05). Although luminal Ba (2 mM) decreased K secretion (from -14.4 +/- 2.9 to -7.0 +/- 1.7 peq.mm-1.min-1), basolateral insulin (10(-6) M) inhibited K secretion further (to -4.7 +/- 1.3 peq.mm-1.min-1, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

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Ca(2+)-activated nonselective cation channel in apical membrane of vestibular dark cells

AJP Cell Physiology ◽

10.1152/ajpcell.1992.262.6.c1423 ◽

1992 ◽

Vol 262 (6) ◽

pp. C1423-C1429 ◽

Cited By ~ 28

Author(s):

D. C. Marcus ◽

S. Takeuchi ◽

P. Wangemann

Keyword(s):

Single Channel ◽

Apical Membrane ◽

Cation Channel ◽

Nonselective Cation Channel ◽

Channel Activity ◽

Dark Cells ◽

Linear Current ◽

Current Voltage ◽

K Secretion ◽

Vestibular Dark Cells

Patch-clamp recordings were made on cell-attached and excised apical membrane from dark cells of the semicircular canal of the gerbil. These cells are thought to secrete K+ and absorb Na+ from the luminal fluid (endolymph). Single-channel events were identified as being equally conductive (27.6 +/- 0.4 pS; n = 48) for K+, Na+, Rb+, Li+, and Cs+ and 1.4 times more permeable to NH4+ but not permeable to Cl-, Ca2+, Ba2+, nor to N-methyl-D-glucamine. The channels displayed linear current-voltage relations that passed nearly through the origin (intercept: -2.6 +/- 0.5 mV; n = 48) when conductive monovalent cations were present on both sides of the membrane in equal concentrations. Channel activity required the presence of Ca2+ at the cytosolic face; there was no activity at less than or equal to 10(-7) M Ca2+ and full activity at greater than or equal to 10(-5) M Ca2+. Cell-attached recordings had a mean reversal voltage of -36.4 +/- 7.9 mV (n = 7), which was interpreted to reflect the intracellular potential of dark cells under the present conditions. We have identified a nonselective cation channel in the apical membrane of vestibular dark cells that might participate in K+ secretion or Na+ absorption under stimulated conditions, but the density appears to be insufficient to fully account for the transepithelial K+ flux.

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