Epithelial Na+ channels are regulated by flow

2001 ◽  
Vol 280 (6) ◽  
pp. F1010-F1018 ◽  
Author(s):  
Lisa M. Satlin ◽  
Shaohu Sheng ◽  
Craig B. Woda ◽  
Thomas R. Kleyman
Keyword(s):  
Shear Stress ◽  
Hydrostatic Pressure ◽  
Flow Rate ◽  
Collecting Duct ◽  
Reversal Potential ◽  
Cortical Collecting Duct ◽  
Membrane Stretch ◽  
Flow Stimulation ◽  
Biomechanical Forces ◽  
Stimulation Of

Na+ absorption in the renal cortical collecting duct (CCD) is mediated by apical epithelial Na+ channels (ENaCs). The CCD is subject to continuous variations in intraluminal flow rate that we speculate alters hydrostatic pressure, membrane stretch, and shear stress. Although ENaCs share limited sequence homology with putative mechanosensitive ion channels in Caenorhabditis elegans,controversy exists as to whether ENaCs are regulated by biomechanical forces. We examined the effect of varying the rate of fluid flow on whole cell Na+ currents ( I Na) in oocytes expressing mouse α,β,γ-ENaC (mENaC) and on net Na+ absorption in microperfused rabbit CCDs. Oocytes injected with mENaC but not water responded to the initiation of superfusate flow (to 4–6 ml/min) with a reversible threefold stimulation of I Nawithout a change in reversal potential. The increase in I Na was variable among oocytes. CCDs responded to a threefold increase in rate of luminal flow with a twofold increase in the rate of net Na+ absorption. An increase in luminal viscosity achieved by addition of 5% dextran to the luminal perfusate did not alter the rate of net Na+ absorption, suggesting that shear stress does not influence Na+ transport in the CCD. In sum, our data suggest that flow stimulation of ENaC activity and Na+ absorption is mediated by an increase in hydrostatic pressure and/or membrane stretch. We propose that intraluminal flow rate may be an important regulator of channel activity in the CCD.

scholarly journals Mechanoregulation of BK channel activity in the mammalian cortical collecting duct: role of protein kinases A and C

2009 ◽  
Vol 297 (4) ◽  
pp. F904-F915 ◽  
Author(s):  
Wen Liu ◽  
Yuan Wei ◽  
Peng Sun ◽  
Wen-Hui Wang ◽  
Thomas R. Kleyman ◽  
...  
Keyword(s):  
Flow Rate ◽  
Collecting Duct ◽  
Bk Channel ◽  
Slow Flow ◽  
Cortical Collecting Duct ◽  
Flow Rates ◽  
Calphostin C ◽  
Flow Stimulation ◽  
Slow Flow Rate ◽  
Stimulation Of

Flow-stimulated net K secretion ( JK) in the cortical collecting duct (CCD) is mediated by an iberiotoxin (IBX)-sensitive BK channel, and requires an increase in intracellular Ca2+ concentration ([Ca2+]i). The α-subunit of the reconstituted BK channel is phosphorylated by PKA and PKC. To test whether the BK channel in the native CCD is regulated by these kinases, JK and net Na absorption ( JNa) were measured at slow (∼1) and fast (∼5 nl·min−1·mm−1) flow rates in rabbit CCDs microperfused in the presence of mPKI, an inhibitor of PKA; calphostin C, which inhibits diacylglycerol binding proteins, including PKC; or bisindolylmaleimide (BIM) and Gö6976, inhibitors of classic and novel PKC isoforms, added to luminal (L) and/or basolateral (B) solutions. L but not B mPKI increased JK in CCDs perfused at a slow flow rate; a subsequent increase in flow rate augmented JK modestly. B mPKI alone or with L inhibitor abolished flow stimulation of JK. Similarly, L calphostin C increased JK in CCDs perfused at slow flow rates, as did calphostin C in both L and B solutions. The observation that IBX inhibited the L mPKI- and calphostin C-mediated increases in JK at slow flow rates implicated the BK channel in this K flux, a notion suggested by patch-clamp analysis of principal cells. The kinase inhibited by calphostin C was not PKC as L and/or B BIM and Gö6976 failed to enhance JK at the slow flow rate. However, addition of these PKC inhibitors to the B solution alone or with L inhibitor blocked flow stimulation of JK. Interpretation of these results in light of the effects of these inhibitors on the flow-induced elevation of [Ca2+]i suggests that the principal cell apical BK channel is tonically inhibited by PKA and that flow stimulation of JK in the CCD is PKA and PKC dependent. The specific targets of the kinases remain to be identified.

DA1 dopamine receptors in renal cortical collecting duct

1991 ◽  
Vol 261 (5) ◽  
pp. F890-F895 ◽  
Author(s):  
K. Ohbu ◽  
R. A. Felder
Keyword(s):  
Adenylate Cyclase ◽  
Specific Binding ◽  
Collecting Duct ◽  
Sch 23390 ◽  
Receptor Density ◽  
Cortical Collecting Duct ◽  
Tightly Coupled ◽  
Renal Dopamine ◽  
Dissociation Constant Kd ◽  
Stimulation Of

Renal dopamine DA1 receptors are linked to the regulation of sodium transport. We have previously reported the presence of DA1 receptors in the proximal convoluted tubule (PCT) but not in the distal convoluted tubule. However, the DA1 receptor in the collecting duct, the final determinant of electrolyte transport, has not been studied. DA1 receptors were studied in the microdissected cortical collecting duct (CCD) of rats by autoradiography with use of the selective DA1 radioligand 125I-Sch 23982 and by measurement of adenylate cyclase (AC) activity. Specific binding of 125I-Sch 23982 to CCD was saturable with radioligand concentration. The dissociation constant (Kd) was 0.46 +/- 0.08 nM (n = 5), and the maximum receptor density (Bmax) was 1.41 +/- 0.43 fmol/mg protein (n = 5). The DA1 antagonist Sch 23390 was more effective than the DA1 agonist fenoldopam in competing for specific 125I-Sch 23982 binding. Fenoldopam stimulated AC activity in CCD in a concentration-dependent (10(-9)-10(-6) M) manner. The ability of fenoldopam to stimulate AC activity was similar in CCD and PCT even though DA1 receptor density was 1,000 times greater in the CCD than in the PCT. In additional studies, fenoldopam stimulation of AC activity did not influence vasopressin-stimulated AC activity. We conclude that the DA1 receptor in rat CCD is tightly coupled to AC stimulation and that there is no interaction between DA1 agonist-stimulated and vasopressin-stimulated AC activity in the CCD.

Stimulation of Cl- self exchange by intracellular HCO3- in rabbit cortical collecting duct

1989 ◽  
Vol 257 (1) ◽  
pp. C94-C101 ◽  
Author(s):  
K. Matsuzaki ◽  
J. B. Stokes ◽  
V. L. Schuster
Keyword(s):  
Anion Exchange ◽  
Intracellular Ph ◽  
Rate Coefficient ◽  
Collecting Duct ◽  
Cortical Collecting Duct ◽  
High K ◽  
Shift Experiment ◽  
Ethanesulfonic Acid ◽  
The Individual ◽  
Stimulation Of

In rabbit cortical collecting duct, Cl- self exchange accounts for most of the transepithelial Cl- tracer rate coefficient, KCl (nm/s); a small fraction is effected by Cl--HCO3- exchange and Cl- diffusion. We previously reported that changing from a CO2-free N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) bath to a 5% CO2-25 mM HCO3- bath stimulates Cl- self exchange. Here, we examine in further detail the individual components of the CO2-HCO3- system that stimulate KCl. Addition of 0.5% CO2 to a HEPES bath (final pH = 7.24) stimulated KCl by 70 +/- 19 nm/s, a delta KCl comparable to that induced by 1% CO2 (pH 7.12), 6% CO2 (pH 6.6), or 6% CO2-25 mM HCO3- (pH 7.4). The roles of intracellular pH (pHi) and HCO3- concentration were examined by clamping pHi using high K+ and nigericin. Increasing pHi from 6.9 to 7.6 in solutions without exogenous CO2 or HCO3- increased KCl by 71 +/- 17 nm/s. These results suggest that pHi might regulate anion exchange. However, during such a pHi-shift experiment, metabolically derived CO2 produces a concomitant change in intracellular HCO3- concentration [( HCO3-]i). To determine whether an increase in [HCO3-]i could stimulate Cl- self exchange, we replaced HEPES with 6% CO2-5 mM HCO3- isohydrically (pHi clamped at 6.9). With this increase in [HCO3-]i at constant pHi, KCl increased by 51 +/- 10 nm/s. These maneuvers had negligible effects on Cl- diffusion and Cl--HCO3- exchange. These experiments demonstrate that increases in cell [HCO3-] (or perhaps CO2) can stimulate transepithelial anion exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of aldosterone-induced stimulation of ENaC synthesis by changing the rate of apical Na+ entry

2001 ◽  
Vol 281 (4) ◽  
pp. F687-F692 ◽  
Author(s):  
Lisette Dijkink ◽  
Anita Hartog ◽  
Carel H. Van Os ◽  
René J. M. Bindels
Keyword(s):  
Feedback Inhibition ◽  
Collecting Duct ◽  
Short Circuit ◽  
Primary Cultures ◽  
Short Circuit Current ◽  
Inhibitory Effect ◽  
Cortical Collecting Duct ◽  
Entry Rate ◽  
Protein Levels ◽  
Stimulation Of

Primary cultures of immunodissected rabbit connecting tubule and cortical collecting duct cells were used to investigate the effect of apical Na+ entry rate on aldosterone-induced transepithelial Na+ transport, which was measured as benzamil-sensitive short-circuit current ( I sc). Stimulation of the apical Na+ entry, by long-term short-circuiting of the monolayers, suppressed the aldosterone-stimulated benzamil-sensitive I sc from 320 ± 49 to 117 ± 14%, whereas in the presence of benzamil this inhibitory effect was not observed (335 ± 74%). Immunoprecipitation of [35S]methionine-labeled β-rabbit epithelial Na+ channel (rbENaC) revealed that the effects of modulation of apical Na+ entry on transepithelial Na+ transport are exactly mirrored by β-rbENaC protein levels, because short-circuiting the monolayers decreased aldosterone-induced β-rbENaC protein synthesis from 310 ± 51 to 56 ± 17%. Exposure to benzamil doubled the β-rbENaC protein level to 281 ± 68% in control cells but had no significant effect on aldosterone-stimulated β-rbENaC levels (282 ± 68%). In conclusion, stimulation of apical Na+ entry suppresses the aldosterone-induced increase in transepithelial Na+transport. This negative-feedback inhibition is reflected in a decrease in β-rbENaC synthesis or in an increase in β-rbENaC degradation.

Stimulation of total CO2 flux by 10% CO2 in rabbit CCD: role of an apical Sch-28080- and Ba-sensitive mechanism

1994 ◽  
Vol 267 (1) ◽  
pp. F114-F120 ◽  
Author(s):  
X. Zhou ◽  
C. S. Wingo
Keyword(s):  
Collecting Duct ◽  
Co2 Flux ◽  
K Channel ◽  
Co2 Absorption ◽  
Cortical Collecting Duct ◽  
Atpase Inhibitor ◽  
Contrast Exposure ◽  
Stimulation Of

These studies examine the effect of ambient PCO2 on net bicarbonate (total CO2) absorption by the in vitro perfused cortical collecting duct (CCD) from K-replete rabbits and the mechanism responsible for this effect. Exposure to 10% CO2 increased net bicarbonate flux (total CO2 flux, JtCO2) by 1.8-fold (P < 0.005), and this effect was inhibited by luminal 10 microM Sch-28080, an H-K-adenosinetriphosphatase (H-K-ATPase) inhibitor. In contrast, exposure to 10% CO2 significantly decreased Rb efflux, and this decrement in Rb efflux was blocked by luminal 2 mM Ba, a K channel blocker. Thus transepithelial tracer Rb flux did not increase upon exposure to 10% CO2 as we have observed in this segment under K-restricted conditions. The observation that 10% CO2 increased net bicarbonate absorption without a change in absorptive Rb flux suggested that 10% CO2 increased apical K recycling. To test this hypothesis, we examined whether luminal Ba inhibited the stimulation of luminal acidification induced by 10% CO2. If apical K exit were necessary for full activation of proton secretion, then inhibiting K exit should indirectly affect the stimulation of JtCO2 by 10% CO2. In fact, the effect of 10% CO2 on JtCO2 in the presence of 2 mM luminal Ba was quantitatively indistinguishable from the effect of 10% CO2 on JtCO2 in the presence of 10 microM luminal Sch-28080.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Effects of biomechanical forces on signaling in the cortical collecting duct (CCD)

2014 ◽  
Vol 307 (2) ◽  
pp. F195-F204 ◽  
Author(s):  
Rolando Carrisoza-Gaytan ◽  
Yu Liu ◽  
Daniel Flores ◽  
Cindy Else ◽  
Heon Goo Lee ◽  
...  
Keyword(s):  
Fluid Shear Stress ◽  
Ex Vivo ◽  
Collecting Duct ◽  
Cation Transport ◽  
Mapk Signaling ◽  
Collagen Type Iv ◽  
Cortical Collecting Duct ◽  
Type Iv ◽  
Biomechanical Forces

An increase in tubular fluid flow rate (TFF) stimulates Na reabsorption and K secretion in the cortical collecting duct (CCD) and subjects cells therein to biomechanical forces including fluid shear stress (FSS) and circumferential stretch (CS). Intracellular MAPK and extracellular autocrine/paracrine PGE2 signaling regulate cation transport in the CCD and, at least in other systems, are affected by biomechanical forces. We hypothesized that FSS and CS differentially affect MAPK signaling and PGE2 release to modulate cation transport in the CCD. To validate that CS is a physiological force in vivo, we applied the intravital microscopic approach to rodent kidneys in vivo to show that saline or furosemide injection led to a 46.5 ± 2.0 or 170 ± 32% increase, respectively, in distal tubular diameter. Next, murine CCD (mpkCCD) cells were grown on glass or silicone coated with collagen type IV and subjected to 0 or 0.4 dyne/cm2 of FSS or 10% CS, respectively, forces chosen based on prior biomechanical modeling of ex vivo microperfused CCDs. Cells exposed to FSS expressed an approximately twofold greater abundance of phospho(p)-ERK and p-p38 vs. static cells, while CS did not alter p-p38 and p-ERK expression compared with unstretched controls. FSS induced whereas CS reduced PGE2 release by ∼40%. In conclusion, FSS and CS differentially affect ERK and p38 activation and PGE2 release in a cell culture model of the CD. We speculate that TFF differentially regulates biomechanical signaling and, in turn, cation transport in the CCD.

Postnatal maturation of potassium transport in rabbit cortical collecting duct

1994 ◽  
Vol 266 (1) ◽  
pp. F57-F65 ◽  
Author(s):  
L. M. Satlin
Keyword(s):  
Flow Rate ◽  
Collecting Duct ◽  
Cortical Collecting Duct ◽  
Flow Rates ◽  
Postnatal Maturation ◽  
Significant Linear Correlation ◽  
Potassium Secretion ◽  
Tubular Flow ◽  
Neonatal Kidney

Clearance studies in newborns demonstrate low rates of urinary excretion of potassium, suggesting that the neonatal kidney contributes to the conservation of potassium necessary for growth. Because the cortical collecting duct (CCD) is a primary site for potassium secretion in the adult, we sought to examine the transport capacity of this segment for potassium during postnatal maturation. CCDs isolated from rabbits of various ages (5-6 animals/age group) were microperfused in vitro with solutions simulating plasma. The concentrations of potassium in samples of collected fluid, measured by helium glow photometry, were used to calculate net transport. At a flow rate of approximately 1.6 nl.min-1 x mm-1 net potassium secretion was absent at birth, first became evident at 4 wk of age (-11.08 +/- 2.39 pmol.min-1 x mm-1), and increased sharply thereafter to reach mature rates (-23.08 +/- 3.47 pmol.min-1 x mm-1; P < 0.05) by 6 wk of age. To determine whether low distal tubular flow rates limit net potassium secretion in the neonate, we perfused CCDs at two or more flow rates in the 0.5–5 nl.min-1 x mm-1 range. In CCDs taken from animals > or = 6 wk of age, potassium secretion showed a significant linear correlation with flow rate (y = -10.0x - 7.45; r = 0.87; n = 12).(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphate transport in the light segment of the rabbit cortical collecting tubule

1982 ◽  
Vol 242 (4) ◽  
pp. F379-F384
Author(s):  
G. R. Shareghi ◽  
Z. S. Agus
Keyword(s):  
Flow Rate ◽  
Collecting Duct ◽  
Phosphate Transport ◽  
Phosphate Concentration ◽  
Cortical Collecting Duct ◽  
Concentration Gradients ◽  
Collecting Tubule ◽  
Residual Transport ◽  
The Difference ◽  
Rabbit Cortical Collecting Tubule

The mode and mechanism of phosphate transport in the light portion of the rabbit cortical collecting duct were studied with isolated tubular perfusion. Control studies (n = 48) revealed a mean transepithelial potential difference (PD) of -16.5 +/- 1.3 mV and net phosphate absorption (JPO4) of 0.58 +/- 0.07 pmol.mm-1.min-1. To characterize transport, the effects of flow rate, ouabain, amiloride, and phosphate concentration, and parathyroid hormone (PTH) were analyzed. There was a significant linear relationship between JPO4 and flow rate (n = 48) (r = 0.71, P less than 0.025). Increasing the difference between lumen and bath phosphate concentration from -8.0 to +8.0 mg/dl was associated with a stepwise increase in JPO4 from -0.18 +/- 0.02 to 0.93 +/- 0.05 pmol.mm-1.min-1. PTH had no effect on JPO4. To assess the effects of PD, the tubules were treated with either amiloride (n = 6) or ouabain (n = 7). JPO4 fell significant in both circumstances with reduction of PD, although there remained significant residual transport following amiloride addition. The data demonstrate significant phosphate transport in this segment that is independent of PTH and altered by transepithelial electrical and concentration gradients as well as flow rate.

scholarly journals Effects of ammonia on bicarbonate transport in the cortical collecting duct

2000 ◽  
Vol 278 (2) ◽  
pp. F219-F226 ◽  
Author(s):  
Amy E. Frank ◽  
Charles S. Wingo ◽  
I. David Weiner
Keyword(s):  
Collecting Duct ◽  
Potassium Transport ◽  
Bicarbonate Transport ◽  
Cortical Collecting Duct ◽  
Intracellular Acidification ◽  
Bicarbonate Reabsorption ◽  
Atpase Inhibitors ◽  
Collecting Ducts ◽  
Stimulation Of

Both acidosis and hypokalemia stimulate renal ammoniagenesis, and both regulate urinary proton and potassium excretion. We hypothesized that ammonia might play an important role in this processing by stimulating H+-K+-ATPase-mediated ion transport. Rabbit cortical collecting ducts (CCD) were studied using in vitro microperfusion, bicarbonate reabsorption was measured using microcalorimetry, and intracellular pH (pHi) was measured using the fluorescent, pH-sensitive dye, 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Ammonia caused a concentration-dependent increase in net bicarbonate reabsorption that was inhibited by luminal addition of either of the H+-K+-ATPase inhibitors, Sch-28080 or ouabain. The stimulation of net bicarbonate reabsorption was not mediated through apical H+-ATPase, basolateral Na+-K+-ATPase, or luminal electronegativity. Although ammonia caused intracellular acidification, similar changes in pHi induced by inhibiting basolateral Na+/H+ exchange did not alter net bicarbonate reabsorption. We conclude that ammonia regulates CCD proton and potassium transport, at least in part, by stimulating apical H+-K+-ATPase.

scholarly journals An unexpected journey: conceptual evolution of mechanoregulated potassium transport in the distal nephron

2016 ◽  
Vol 310 (4) ◽  
pp. C243-C259 ◽  
Author(s):  
Rolando Carrisoza-Gaytan ◽  
Marcelo D. Carattino ◽  
Thomas R. Kleyman ◽  
Lisa M. Satlin
Keyword(s):  
Flow Rate ◽  
Fluid Shear Stress ◽  
Collecting Duct ◽  
Critical Role ◽  
Bk Channels ◽  
Bk Channel ◽  
Macromolecular Complex ◽  
Urinary Flow ◽  
Cortical Collecting Duct ◽  
Distal Nephron

Flow-induced K secretion (FIKS) in the aldosterone-sensitive distal nephron (ASDN) is mediated by large-conductance, Ca2+/stretch-activated BK channels composed of pore-forming α-subunits (BKα) and accessory β-subunits. This channel also plays a critical role in the renal adaptation to dietary K loading. Within the ASDN, the cortical collecting duct (CCD) is a major site for the final renal regulation of K homeostasis. Principal cells in the ASDN possess a single apical cilium whereas the surfaces of adjacent intercalated cells, devoid of cilia, are decorated with abundant microvilli and microplicae. Increases in tubular (urinary) flow rate, induced by volume expansion, diuretics, or a high K diet, subject CCD cells to hydrodynamic forces (fluid shear stress, circumferential stretch, and drag/torque on apical cilia and presumably microvilli/microplicae) that are transduced into increases in principal (PC) and intercalated (IC) cell cytoplasmic Ca2+ concentration that activate apical voltage-, stretch- and Ca2+-activated BK channels, which mediate FIKS. This review summarizes studies by ourselves and others that have led to the evolving picture that the BK channel is localized in a macromolecular complex at the apical membrane, composed of mechanosensitive apical Ca2+ channels and a variety of kinases/phosphatases as well as other signaling molecules anchored to the cytoskeleton, and that an increase in tubular fluid flow rate leads to IC- and PC-specific responses determined, in large part, by the cell-specific composition of the BK channels.

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