scholarly journals Role of KCNE1-Dependent K+ Fluxes in Mouse Proximal Tubule

2001 ◽  
Vol 12 (10) ◽  
pp. 2003-2011
Author(s):  
VOLKER VALLON ◽  
FLORIAN GRAHAMMER ◽  
KERSTIN RICHTER ◽  
MARKUS BLEICH ◽  
FLORIAN LANG ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Coupled Transport ◽  
Wild Type ◽  
Electrochemical Gradient ◽  
Volume Depletion ◽  
Luminal Membrane ◽  
Clearance Studies ◽  
Electrophysiological Studies ◽  
Kidney Micropuncture

Abstract. The electrochemical gradient for K+ across the luminal membrane of the proximal tubule favors K+ fluxes to the lumen. Here it was demonstrated by immunohistochemistry that KCNE1 and KCNQ1, which form together the slowly activated component of the delayed rectifying K+ current in the heart, also colocalize in the luminal membrane of proximal tubule in mouse kidney. Micropuncture experiments revealed a reduced K+ concentration in late proximal and early distal tubular fluid as well as a reduced K+ delivery to these sites in KCNE1 knockout (-/-), compared with wild-type (+/+) mice. These observations would be consistent with KCNE1-dependent K+ fluxes to the lumen in proximal tubule. Electrophysiological studies in isolated perfused proximal tubules indicated that this K+ flux is essential to counteract membrane depolarization due to electrogenic Na+-coupled transport of glucose or amino acids. Clearance studies revealed an enhanced fractional urinary excretion of fluid, Na+, Cl-, and glucose in KCNE1 -/- compared with KCNE1 +/+ mice that may relate to an attenuated transport in proximal tubule and contribute to volume depletion in these mice, as indicated by higher hematocrit values.

Mechanism of proximal tubule bicarbonate absorption in NHE3 null mice

1999 ◽  
Vol 277 (2) ◽  
pp. F298-F302 ◽  
Author(s):  
Tong Wang ◽  
Chao-Ling Yang ◽  
Thecla Abbiati ◽  
Patrick J. Schultheis ◽  
Gary E. Shull ◽  
...  
Keyword(s):  
Atpase Activity ◽  
Proximal Tubule ◽  
Apical Membrane ◽  
Significant Inhibition ◽  
Fluid Absorption ◽  
Wild Type ◽  
Significant Component ◽  
Nhe Isoforms

NHE3 is the predominant isoform responsible for apical membrane Na+/H+exchange in the proximal tubule. Deletion of NHE3 by gene targeting results in an NHE3−/−mouse with greatly reduced proximal tubule[Formula: see text] absorption compared with NHE3+/+ animals (P. J. Schultheis, L. L. Clarke, P. Meneton, M. L. Miller, M. Soleimani, L. R. Gawenis, T. M. Riddle, J. J. Duffy, T. Doetschman, T. Wang, G. Giebisch, P. S. Aronson, J. N. Lorenz, and G. E. Shull. Nature Genet. 19: 282–285, 1998). The purpose of the present study was to evaluate the role of other acidification mechanisms in mediating the remaining component of proximal tubule [Formula: see text] reabsorption in NHE3−/− mice. Proximal tubule transport was studied by in situ microperfusion. Net rates of[Formula: see text] ( J HCO3) and fluid absorption ( J v) were reduced by 54 and 63%, respectively, in NHE3 null mice compared with controls. Addition of 100 μM ethylisopropylamiloride (EIPA) to the luminal perfusate caused significant inhibition of J HCO3 and J v in NHE3+/+ mice but failed to inhibit J HCO3 or J v in NHE3−/− mice, indicating lack of activity of NHE2 or other EIPA-sensitive NHE isoforms in the null mice. Addition of 1 μM bafilomycin caused a similar absolute decrement in J HCO3 in wild-type and NHE3 null mice, indicating equivalent rates of[Formula: see text] absorption mediated by H+-ATPase. Addition of 10 μM Sch-28080 did not reduce J HCO3 in either wild-type or NHE3 null mice, indicating lack of detectable H+-K+-ATPase activity in the proximal tubule. We conclude that, in the absence of NHE3, neither NHE2 nor any other EIPA-sensitive NHE isoform contributes to mediating [Formula: see text] reabsorption in the proximal tubule. A significant component of[Formula: see text] reabsorption in the proximal tubule is mediated by bafilomycin-sensitive H+-ATPase, but its activity is not significantly upregulated in NHE3 null mice.

scholarly journals A kinetically defined Na+/H+ antiporter within a mathematical model of the rat proximal tubule.

1995 ◽  
Vol 105 (5) ◽  
pp. 617-641 ◽  
Author(s):  
A M Weinstein
Keyword(s):  
Kinetic Model ◽  
Proximal Tubule ◽  
Membrane Vesicles ◽  
Model Calculations ◽  
Kinetic Formulation ◽  
Luminal Membrane ◽  
Least Squares Fit ◽  
Velocity Effect ◽  
Rat Proximal Tubule

The luminal membrane antiporter of the proximal tubule has been represented using the kinetic formulation of E. Heinz (1978. Mechanics and Engergetics of Biological Transport. Springer-Verlag, Berlin) with the assumption of equilibrium binding and 1:1 stoichiometry. Competitive binding and transport of NH+4 is included within this model. Ion affinities and permeation velocities were selected in a least-squares fit to the kinetic parameters determined experimentally in renal membrane vesicles (Aronson, P.S., M.A. Suhm, and J. Nee. 1983. Journal of Biological Chemistry. 258:6767-6771). The modifier role of internal H+ to enhance transport beyond the expected kinetics (Aronson, P.S., J. Nee, and M. A. Suhm. 1982. Nature. 299:161-163) is represented as a velocity effect of H+ binding to a single site. This kinetic formulation of the Na+/H+ antiporter was incorporated within a model of the rat proximal tubule (Weinstein, A. M. 1994. American Journal of Physiology. 267:F237-F248) as a replacement for the representation by linear nonequilibrium thermodynamics (NET). The membrane density of the antiporter was selected to yield agreement with the rate of tubular Na+ reabsorption. Simulation of 0.5 cm of tubule predicts that the activity of the Na+/H+ antiporter is the most important force for active secretion of ammonia. Model calculations of metabolic acid-base disturbances are performed and comparison is made among antiporter representations (kinetic model, kinetic model without internal modifier, and NET formulation). It is found that the ability to sharply turn off Na+/H+ exchange in cellular alkalosis substantially eliminates the cell volume increase associated with high HCO3- conditions. In the tubule model, diminished Na+/H+ exchange in alkalosis blunts the axial decrease in luminal HCO3- and thus diminishes paracellular reabsorption of Cl-. In this way, the kinetics of the Na+/H+ antiporter could act to enhance distal delivery of Na+, Cl-, and HCO3- in acute metabolic alkalosis.

scholarly journals Regulation of renal NaDC1 expression and citrate excretion by NBCe1-A

2019 ◽  
Vol 317 (2) ◽  
pp. F489-F501 ◽  
Author(s):  
Gunars Osis ◽  
Kierstin L. Webster ◽  
Autumn N. Harris ◽  
Hyun-Wook Lee ◽  
Chao Chen ◽  
...  
Keyword(s):  
Metabolic Acidosis ◽  
Proximal Tubule ◽  
Wild Type ◽  
Outer Medulla ◽  
Extracellular Signals ◽  
Citrate Metabolism ◽  
Acid Loading ◽  
Convoluted Tubules ◽  
Proximal Tubule Segments

Citrate is critical for acid-base homeostasis and to prevent calcium nephrolithiasis. Both metabolic acidosis and hypokalemia decrease citrate excretion and increase expression of Na+-dicarboxylate cotransporter 1 (NaDC1; SLC13A2), the primary protein involved in citrate reabsorption. However, the mechanisms transducing extracellular signals and mediating these responses are incompletely understood. The purpose of the present study was to determine the role of the Na+-coupled electrogenic bicarbonate cotransporter (NBCe1) A variant (NBCe1-A) in citrate metabolism under basal conditions and in response to acid loading and hypokalemia. NBCe1-A deletion increased citrate excretion and decreased NaDC1 expression in the proximal convoluted tubules (PCT) and proximal straight tubules (PST) in the medullary ray (PST-MR) but not in the PST in the outer medulla (PST-OM). Acid loading wild-type (WT) mice decreased citrate excretion. NaDC1 expression increased only in the PCT and PST-MR and not in the PST-MR. In NBCe1-A knockout (KO) mice, the acid loading change in citrate excretion was unaffected, changes in PCT NaDC1 expression were blocked, and there was an adaptive increase in PST-MR. Hypokalemia in WT mice decreased citrate excretion; NaDC1 expression increased only in the PCT and PST-MR. NBCe1-A KO blocked both the citrate and NaDC1 changes. We conclude that 1) adaptive changes in NaDC1 expression in response to metabolic acidosis and hypokalemia occur specifically in the PCT and PST-MR, i.e., in cortical proximal tubule segments; 2) NBCe1-A is necessary for normal basal, metabolic acidosis and hypokalemia-stimulated citrate metabolism and does so by regulating NaDC1 expression in cortical proximal tubule segments; and 3) adaptive increases in PST-OM NaDC1 expression occur in NBCe1-A KO mice in response to acid loading that do not occur in WT mice.

scholarly journals NBCe1-A is required for the renal ammonia and K+ response to hypokalemia

2020 ◽  
Vol 318 (2) ◽  
pp. F402-F421 ◽  
Author(s):  
Hyun-Wook Lee ◽  
Autumn N. Harris ◽  
Michael F. Romero ◽  
Paul A. Welling ◽  
Charles S. Wingo ◽  
...  
Keyword(s):  
Metabolic Acidosis ◽  
Proximal Tubule ◽  
Splice Variant ◽  
Ammonia Excretion ◽  
Wild Type ◽  
Outer Medulla ◽  
Ammonia Metabolism ◽  
Tissue Sections ◽  
K Response

Hypokalemia increases ammonia excretion and decreases K+ excretion. The present study examined the role of the proximal tubule protein NBCe1-A in these responses. We studied mice with Na+-bicarbonate cotransporter electrogenic, isoform 1, splice variant A (NBCe1-A) deletion [knockout (KO) mice] and their wild-type (WT) littermates were provided either K+ control or K+-free diet. We also used tissue sections to determine the effect of extracellular ammonia on NaCl cotransporter (NCC) phosphorylation. The K+-free diet significantly increased proximal tubule NBCe1-A and ammonia excretion in WT mice, and NBCe1-A deletion blunted the ammonia excretion response. NBCe1-A deletion inhibited the ammoniagenic/ammonia recycling enzyme response in the cortical proximal tubule (PT), where NBCe1-A is present in WT mice. In the outer medulla, where NBCe1-A is not present, the PT ammonia metabolism response was accentuated by NBCe1-A deletion. KO mice developed more severe hypokalemia and had greater urinary K+ excretion during the K+-free diet than did WT mice. This was associated with blunting of the hypokalemia-induced change in NCC phosphorylation. NBCe1-A KO mice have systemic metabolic acidosis, but experimentally induced metabolic acidosis did not alter NCC phosphorylation. Although KO mice have impaired ammonia metabolism, experiments in tissue sections showed that lack of ammonia does impair NCC phosphorylation. Finally, urinary aldosterone was greater in KO mice than in WT mice, but neither expression of epithelial Na+ channel α-, β-, and γ-subunits nor of H+-K+-ATPase α1- or α2-subunits correlated with changes in urinary K+. We conclude that NBCe1-A is critical for the effect of diet-induced hypokalemia to increase cortical proximal tubule ammonia generation and for the expected decrease in urinary K+ excretion.

Effect of norepinephrine on intracellular pH in kidney proximal tubule: role of Na+-( HCO 3 − ) n cotransport

1998 ◽  
Vol 275 (1) ◽  
pp. F33-F45 ◽  
Author(s):  
Solange Abdulnour-Nakhoul ◽  
Raja N. Khuri ◽  
Nazih L. Nakhoul
Keyword(s):  
Membrane Potential ◽  
Proximal Tubule ◽  
Intracellular Ph ◽  
Basolateral Membrane ◽  
Inhibitory Effect ◽  
Rate Of Change ◽  
Kidney Proximal Tubule ◽  
Luminal Membrane ◽  
Basolateral Membrane Potential

We examined the effect of norepinephrine (NE) on intracellular pH (pHi) and activity of Na+([Formula: see text]) in the isolated perfused kidney proximal tubule of Ambystoma, using single-barreled voltage and ion-selective microelectrodes. In control[Formula: see text] Ringer, addition of 10−6 M NE to the bath reversibly depolarized the basolateral membrane potential ( V 1), the luminal membrane potential ( V 2), and the transepithelial potential difference ( V 3) and increased pHi by 0.14 ± 0.02. These effects were mimicked by isoproterenol but were abolished after pretreatment with SITS or in the absence of CO2/[Formula: see text]. Removal of bath Na+ depolarized V 1 and V 2, hyperpolarized V 3, and decreased pHi. These effects are largely mediated by the electrogenic Na+-([Formula: see text]) n cotransporter. In the presence of NE, the effects of Na+ removal on membrane potential differences and the rate of change of pHi were significantly smaller. Reducing bath [Formula: see text] concentration from 10 to 2 mM at constant CO2 (pH 6.8) depolarized V 1 and V 2, decreased pHi, and lowered[Formula: see text]. These changes are also due to Na+-([Formula: see text]) n . In the presence of NE, reducing bath [[Formula: see text]] caused a smaller depolarizations of V 1 and V 2, and the rate of pHi decrease was significantly reduced. Our results indicate: 1) NE causes an increase in pHi; 2) the NE-induced alkalinization is mediated by a SITS-sensitive and[Formula: see text]-dependent transporter on the basolateral membrane; and 3) in the presence of NE, the reduced effects caused by basolateral[Formula: see text] changes or Na+ removal are indicative of an inhibitory effect of NE on Na+-([Formula: see text]) n cotransport.

Effect of metabolic acidosis on glucose reabsorption in rats with acute hyperglycemia

1990 ◽  
Vol 68 (1) ◽  
pp. 79-83 ◽  
Author(s):  
P. O. Magner ◽  
M. L. Halperin
Keyword(s):  
Proximal Tubule ◽  
Fractional Excretion ◽  
Electrochemical Gradient ◽  
Osmotic Diuresis ◽  
Acute Hyperglycemia ◽  
Luminal Membrane ◽  
Glucose Reabsorption ◽  
Other Substances ◽  
Hyperglycemic Hyperosmolar Nonketotic Coma ◽  
Filtered Load

The rate of reabsorption of glucose in the kidney is a factor to consider with respect to the degree of hyperglycemia in poorly controlled diabetics. The rate of reabsorption of glucose in the proximal tubule is driven by the electrochemical gradient for sodium across the luminal membrane. This gradient in the proximal tubule is also used to reabsorb a number of other substances, quantitatively the most important being bicarbonate. We wished to explore the hypothesis that acidosis, by reducing the filtered load of bicarbonate and therefore the reabsorption of bicarbonate in the proximal tubule, might permit an increased rate of reabsorption of glucose. Hyperglycemia was induced in rats by the infusion of hypertonic glucose. Reabsorption of glucose was measured by clearance methods and factored for glomerular filtration rate (GFR), which has a direct effect on the reabsorption of glucose. The reabsorption of glucose was increased in the kidney when the reabsorption of bicarbonate in the proximal tubule was decreased by either HCl-induced acidosis or the administration of a carbonic anhydrase inhibitor. This effect was independent of a change in GFR and the fractional excretion of Na, factors that may also lead to changes in the reabsorption of glucose by the kidney.Key words: diabetes mellitus, hyperglycemic hyperosmolar nonketotic coma, diabetic ketoacidosis, proximal convoluted tubule, hyperglycemia, glucosuria, osmotic diuresis.

P-gp-induced modulation of regulatory volume increase occurs via PKC in mouse proximal tubule

2002 ◽  
Vol 282 (1) ◽  
pp. F65-F76 ◽  
Author(s):  
Yukio Miyata ◽  
Koji Okada ◽  
Shun Ishibashi ◽  
Yasushi Asano ◽  
Shigeaki Muto
Keyword(s):  
Proximal Tubule ◽  
Wild Type ◽  
Phosphatidylinositol 3 Kinase ◽  
Glycoprotein P ◽  
Volume Increase ◽  
Regulatory Volume Increase ◽  
Kinase C ◽  
P Glycoprotein ◽  
Pkc Inhibitors

The present study examined the role of protein kinase C (PKC) in the P-glycoprotein (P-gp)-induced modulation of regulatory volume increase (RVI) in the isolated nonperfused proximal tubule S2 segments from mice lacking both mdr1a and mdr1b genes (KO) and wild-type (WT) mice. The hyperosmotic solution (500 mosmol/kgH2O) involving 200 mM mannitol activated PKC and elicited RVI in the tubules from KO mice but not from WT mice. The addition of the hyperosmotic solution including the PKC activator phorbol 12-myristate 13-acetate (PMA) to the tubules of the WT mice activated PKC and elicited RVI. The hyperosmotic solution in the presence of the P-gp inhibitors (verapamil or cyclosporin A) elicited RVI in the tubules from the WT mice but not from the KO mice. The PMA- and the P-gp inhibitors-induced RVI was abolished by cotreatment with the PKC inhibitors (staurosporine or calphostin C). In the tubules of the KO mice, the PKC inhibitors abolished RVI, but PMA did not. In the tubules of the WT mice, the microtubule disruptor (colchicine), the microfilament disruptor (cytochalasin B), the phosphatidylinositol 3-kinase (PI 3-kinase) blocker (wortmannin), but not another PI 3-kinase blocker (LY-294002), inhibited the PMA-induced RVI. In the tubules of the KO mice, colchicine, cytochalsin B, and wortmannin abolished RVI, but LY-294002 did not. We conclude that 1) in the mouse proximal tubule, P-gp-induced modulation of RVI occurs via PKC; and 2) the microtubule, microfilament, and wortmannin-sensitive, LY-294002-insensitive PI 3-kinase contribute to the PKC-induced RVI.

scholarly journals Characterization of renal NaCl and oxalate transport in Slc26a6−/− mice

2019 ◽  
Vol 316 (1) ◽  
pp. F128-F133 ◽  
Author(s):  
Felix Knauf ◽  
Heino Velazquez ◽  
Victoria Pfann ◽  
Zhirong Jiang ◽  
Peter S. Aronson
Keyword(s):  
Blood Pressure ◽  
Proximal Tubule ◽  
Fractional Excretion ◽  
Wild Type ◽  
Nacl Transport ◽  
Lower Blood ◽  
Urine Oxalate

The apical membrane Cl−/oxalate exchanger SLC26A6 has been demonstrated to play a role in proximal tubule NaCl transport based on studies in microperfused tubules. The present study is directed at characterizing the role of SLC26A6 in NaCl homeostasis in vivo under physiological conditions. Free-flow micropuncture studies revealed that volume and Cl− absorption were similar in surface proximal tubules of wild-type and Slc26a6−/− mice. Moreover, the increments in urine flow rate and sodium excretion following thiazide and furosemide infusion were identical in wild-type and Slc26a6−/− mice, indicating no difference in NaCl delivery out of the proximal tubule. The absence of an effect of deletion of SLC26A6 on NaCl homeostasis was further supported by the absence of lower blood pressure in Slc26a6−/− compared with wild-type mice on normal or low-salt diets. Moreover, raising plasma and urine oxalate by feeding mice a diet enriched in soluble oxalate did not affect mean blood pressure. In contrast to the lack of effect of SLC26A6 deletion on NaCl homeostasis, fractional excretion of oxalate was reduced from 1.6 in wild-type mice to 0.7 in Slc26a6−/− mice. We conclude that, although SLC26A6 is dispensable for renal NaCl homeostasis, it is required for net renal secretion of oxalate.

Formate-stimulated NaCl absorption in the proximal tubule is independent of the pendrin protein

2002 ◽  
Vol 283 (5) ◽  
pp. F952-F956 ◽  
Author(s):  
Lawrence P. Karniski ◽  
Tong Wang ◽  
Lorraine A. Everett ◽  
Eric D. Green ◽  
Gerhard Giebisch ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Chloride Transport ◽  
Exchange Process ◽  
Membrane Vesicles ◽  
Protein Product ◽  
Wild Type ◽  
Nacl Absorption ◽  
Deficient Mice ◽  
Pds Gene

A significant fraction of active chloride reabsorption across the apical membrane of the proximal tubule is mediated by a chloride/formate exchange process, whereby intracellular formate drives the transport of chloride into the cell. When chloride/formate exchange operates in parallel with Na+/H+ exchange and H+-coupled recycling of formate, the net result is electroneutral NaCl reabsorption. Pendrin is the protein product of the PDS gene (SLC26A4) and functions in several different anion exchange modes, including chloride/formate exchange. Pendrin is expressed in the kidney and may serve as the transporter responsible for formate-dependent NaCl reabsorption. In the present study, Pds-knockout mice were used to determine the role of pendrin in proximal tubule chloride reabsorption. We show that formate-dependent NaCl absorption in microperfused proximal tubules is similar between wild-type and pendrin-deficient mice. In addition, there is no difference in the rate of formate-mediated chloride transport in brush-border membrane vesicles isolated from wild-type and pendrin-deficient mice. These studies demonstrate that pendrin is not responsible for formate-dependent NaCl reabsorption in the proximal tubule.

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