Distribution of transcellular calcium and sodium  transport pathways along mouse distal nephron

First published August 15, 2001; 10.1152/ajprenal. 00085.2001.—The organization of Na+ and Ca2+ transport pathways along the mouse distal nephron is incompletely known. We revealed by immunohistochemistry a set of Ca2+ and Na+transport proteins along the mouse distal convolution. The thiazide-sensitive Na+-Cl− cotransporter (NCC) characterized the distal convoluted tubule (DCT). The amiloride-sensitive epithelial Na+ channel (ENaC) colocalized with NCC in late DCT (DCT2) and extended to the downstream connecting tubule (CNT) and collecting duct (CD). In early DCT (DCT1), the basolateral Ca2+-extruding proteins [Na+/Ca2+ exchanger (NCX), plasma membrane Ca2+-ATPase (PCMA)] and the cytoplasmic Ca2+-binding protein calbindin D28K (CB) were found at very low levels, whereas the cytoplasmic Ca2+/Mg2+-binding protein parvalbumin was highly abundant. NCX, PMCA, and CB prevailed in DCT2 and CNT, where we located the apical epithelial Ca2+ channel (ECaC1). Its subcellular localization changed from apical in DCT2 to exclusively cytoplasmic at the end of CNT. NCX and PMCA decreased in parallel with the fading of ECaC1 in the apical membrane. All three of them were undetectable in CD. These findings disclose DCT2 and CNT as major sites for transcellular Ca2+ transport in the mouse distal nephron. Cellular colocalization of Ca2+ and Na+ transport pathways suggests their mutual interactions in transport regulation.

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Chloride-depletion alkalosis with a normal extracellular fluid volume

AJP Renal Physiology ◽

10.1152/ajprenal.1983.245.4.f419 ◽

1983 ◽

Vol 245 (4) ◽

pp. F419-F424

Author(s):

R. G. Luke ◽

J. H. Galla

Keyword(s):

Volume Expansion ◽

Collecting Duct ◽

Extracellular Fluid ◽

Limited Capacity ◽

Distal Nephron ◽

Chloride Depletion ◽

Chloride Salts ◽

Distal Convolution ◽

Sodium And Potassium ◽

Permissive Role

Current concepts hold that volume expansion is essential to the correction of chloride-depletion alkalosis (CDA) with chloride repletion in a permissive role. In this scheme, intranephronal fluid reabsorption would be redistributed with increased delivery to the distal nephron where the provided chloride is readily reabsorbed and the limited capacity for bicarbonate reabsorption would promote bicarbonate excretion and correction of CDA. In a model of CDA produced by peritoneal dialysis against 0.15 M NaHCO3, we have shown complete correction of CDA within 24 h without volume expansion by either oral isotonic sodium or chloride salts with 70 mM chloride and despite an obligatory bicarbonate load and negative sodium and potassium balance. During correction of CDA without volume expansion in rats by intravenous isotonic fluids containing 80 mM chloride, fractional fluid and chloride reabsorptions in the proximal convoluted tubule and in the loop segment of superficial nephrons were not different from controls but chloride reabsorption was enhanced in the collecting duct segment and probably within the distal convolution. Despite no differences in serial hematocrits, blood pressure, and measured plasma volume, kidney and nephron glomerular filtration rate (GFR) were reduced in CDA and returned to normal upon recovery 24 h later.(ABSTRACT TRUNCATED AT 250 WORDS)

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Expression of the insulin-like growth factor system in the hypokalemic rat kidney

AJP Renal Physiology ◽

10.1152/ajprenal.1997.272.5.f661 ◽

1997 ◽

Vol 272 (5) ◽

pp. F661-F667 ◽

Cited By ~ 3

Author(s):

R. M. Rohan ◽

T. G. Unterman ◽

L. Liu ◽

M. K. Hise

Keyword(s):

Growth Factor ◽

Binding Protein ◽

Collecting Duct ◽

Rat Kidney ◽

Insulin Like Growth Factor ◽

Distal Nephron ◽

Igf System ◽

Igf I ◽

Igf Binding ◽

Igf Binding Protein

We studied the renal expression of the insulin-like growth factor (IGF) system to gain a better perspective of its potential role in the hyperplastic adaptation of the distal nephron to potassium deficiency. Rats were pair fed 1% or 0.002% potassium diets for periods up to 10 days. IGF-I mRNA was diminished in potassium-deficient rats within 4 days, whereas mRNA for IGF binding protein-1 (IGFBP-1), a collecting duct-associated protein, was increased by day 7. At day 10 mRNA for IGFBP-1 in potassium-deficient animals averaged 2.07 +/- 0.53 (mean +/- SD, relative densitometry units) compared with 0.89 +/- 0.26 in control rats (n = 4, P = 0.002). Conversely, IGFBP-3, a binding protein whose mRNA has been localized to the interstitial compartment, averaged 2.40 +/- 0.02 in potassium-deficient rats and 4.77 +/- 0.05 in controls (n = 4, P < 0.03) at day 10 of treatment. Immunohistochemistry performed using a specific IGFBP-1 antibody revealed hyperplasia of distal nephron segments along with an increase in IGFBP-1 in potassium-depleted rats. These data suggest that IGFBP-1 may play an important role in the control of cellular adaptations in the hypokalemic rat kidney either directly by influencing cell migration or indirectly by localizing IGF-I to the distal nephron.

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Sodium and calcium transport pathways along the mammalian distal nephron: from rabbit to human

AJP Renal Physiology ◽

10.1152/ajprenal.00217.2002 ◽

2003 ◽

Vol 284 (4) ◽

pp. F628-F643 ◽

Cited By ~ 123

Author(s):

Johannes Loffing ◽

Brigitte Kaissling

Keyword(s):

Sodium Transport ◽

Calcium Transport ◽

Transport Proteins ◽

Sodium Balance ◽

Apical Plasma Membrane ◽

Calcium Excretion ◽

Fluid Composition ◽

Calcium Balance ◽

Distal Nephron ◽

Transport Pathways

The final adjustment of renal sodium and calcium excretion is achieved by the distal nephron, in which transepithelial ion transport is under control of various hormones, tubular fluid composition, and flow rate. Acquired or inherited diseases leading to deranged renal sodium and calcium balance have been linked to dysfunction of the distal nephron. Diuretic drugs elicit their effects on sodium balance by specifically inhibiting sodium transport proteins in the apical plasma membrane of distal nephron segments. The identification of the major apical sodium transport proteins allows study of their precise distribution pattern along the distal nephron and helps address their cellular and molecular regulation under various physiological and pathophysiological settings. This review focuses on the topological arrangement of sodium and calcium transport proteins along the cortical distal nephron and on some aspects of their functional regulation. The availability of data on the distribution of transporters in various species points to the strengths, as well as to the limitations, of animal models for the extrapolation to humans.

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Expression of transcellular and paracellular calcium and magnesium transport proteins in renal and intestinal epithelia during lactation

AJP Renal Physiology ◽

10.1152/ajprenal.00680.2016 ◽

2017 ◽

Vol 313 (3) ◽

pp. F629-F640 ◽

Cited By ~ 9

Author(s):

Megan R. Beggs ◽

Ida Appel ◽

Per Svenningsen ◽

Karsten Skjødt ◽

R. Todd Alexander ◽

...

Keyword(s):

Breast Milk ◽

Transient Receptor Potential ◽

Receptor Potential ◽

Fractional Excretion ◽

Transport Proteins ◽

Transient Receptor Potential Vanilloid ◽

Mrna Levels ◽

Transport Pathways ◽

Molecular Alterations ◽

Calbindin D

Significant alterations in maternal calcium (Ca2+) and magnesium (Mg2+) balance occur during lactation. Ca2+ is the primary divalent cation mobilized into breast milk by demineralization of the skeleton and alterations in intestinal and renal Ca2+ transport. Mg2+ is also concentrated in breast milk, but the underlying mechanisms are not well understood. To determine the molecular alterations in Ca2+ and Mg2+ transport in the intestine and kidney during lactation, three groups of female mice consisting of either nonpregnant controls, lactating mice, or mice undergoing involution were examined. The fractional excretion of Ca2+, but not Mg2+, rose significantly during lactation. Renal 1-α hydroxylase and 24-OHase mRNA levels increased markedly, as did plasma 1,25 dihydroxyvitamin D levels. This was accompanied by significant increases in intestinal expression of Trpv6 and S100g in lactating mice. However, no alterations in the expression of cation-permeable claudin-2, claudin-12, or claudins-15 were found in the intestine. In the kidney, increased expression of Trpv5 and Calb1 was observed during lactation, while no changes in claudins involved in Ca2+ and Mg2+ transport (claudin-2, claudin-14, claudin-16, or claudin-19) were found. Consistent with the mRNA expression, expression of both calbindin-D28K and transient receptor potential vanilloid 5 (TRPV5) proteins increased. Colonic Trpm6 expression increased during lactation, while renal Trpm6 remained unaltered. In conclusion, proteins involved in transcellular Ca2+ and Mg2+ transport pathways increase during lactation, while expression of paracellular transport proteins remained unchanged. Increased fractional Ca2+ excretion can be explained by vitamin D-dependent intestinal hyperabsorption and bone demineralization, despite enhanced transcellular Ca2+ uptake by the kidney.

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Differential regulation of ROMK (Kir1.1) in distal nephron segments by dietary potassium

AJP Renal Physiology ◽

10.1152/ajprenal.00592.2010 ◽

2011 ◽

Vol 300 (6) ◽

pp. F1385-F1393 ◽

Cited By ~ 61

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.

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PKA-dependent ENaC trafficking requires the SNARE-binding protein complexin

AJP Renal Physiology ◽

10.1152/ajprenal.00390.2003 ◽

2005 ◽

Vol 289 (5) ◽

pp. F969-F977 ◽

Cited By ~ 38

Author(s):

M. B. Butterworth ◽

R. A. Frizzell ◽

J. P. Johnson ◽

K. W. Peters ◽

R. S. Edinger

Keyword(s):

Apical Membrane ◽

Binding Protein ◽

Collecting Duct ◽

Short Circuit ◽

Membrane Vesicle ◽

Channel Number ◽

Synaptic Membranes ◽

Xenopus Laevis Oocytes ◽

Apical Surface ◽

Regulated Trafficking

Acute regulation of epithelial sodium channel (ENaC) function at the apical surface of polarized kidney cortical collecting duct (CCD) epithelial cells occurs in large part by changes in channel number, mediated by membrane vesicle trafficking. Several soluble N-ethyl-maleimide-sensitive factor attachment protein receptors (SNARE) have been implicated in this process. A novel SNARE-binding protein, complexin, has been identified in nervous tissue which specifically binds to and stabilizes SNARE complexes at synaptic membranes to promote vesicle fusion. To test whether this protein is present in mouse CCD (mCCD) cells and its possible involvement in acute ENaC regulation, we cloned complexin (isoform II) from a mouse kidney cDNA library. Complexin II mRNA coexpressed with α-, β-, and γ-ENaC subunits in Xenopus laevis oocytes reduced sodium currents to 16 ± 3% ( n = 19) of control values. Short-circuit current ( Isc) measurements on mCCD cell lines stably over- or underexpressing complexin produced similar results. Basal Isc was reduced from 12.0 ± 1.0 ( n = 15) to 2.0 ± 0.4 ( n = 15) and 1.8 ± 0.3 ( n = 17) μA/cm2, respectively. Similarly forskolin-stimulated Isc was reduced from control values of 20.0 ± 2 to 2.7 ± 0.5 and 2.3 ± 0.4 μA/cm2 by either increasing or decreasing complexin expression. Surface biotinylation demonstrated that the complexin-induced reduction in basal Iscwas due to a reduction in apical membrane-resident ENaC and the inhibition in forskolin stimulation was due to the lack of ENaC insertion into the apical membrane to increase surface channel number. Immunofluorescent localization of SNARE proteins in polarized mCCD epithelia detected the presence of syntaxins 1 and 3 and synaptosomal-associated protein of 23 kDa (SNAP-23) at the apical membrane, and vesicle-associated membrane protein (VAMP2) was localized to intracellular compartments. These findings identify SNAREs that may mediate ENaC-containing vesicle insertion in mCCD epithelia and suggest that stabilization of SNARE interactions by complexin is an essential aspect of the regulated trafficking events that increase apical membrane ENaC density either by constitutive or regulated trafficking pathways.

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Mammalian Distal Tubule: Physiology, Pathophysiology, and Molecular Anatomy

Physiological Reviews ◽

10.1152/physrev.2000.80.1.277 ◽

2000 ◽

Vol 80 (1) ◽

pp. 277-313 ◽

Cited By ~ 251

Author(s):

Robert F. Reilly ◽

David H. Ellison

Keyword(s):

Ion Transport ◽

Collecting Duct ◽

Mammalian Species ◽

Distal Tubule ◽

Cell Types ◽

Molecular Techniques ◽

Molecular Architecture ◽

Distal Nephron ◽

Transport Pathways ◽

Urinary Potassium

The distal tubule of the mammalian kidney, defined as the region between the macula densa and the collecting duct, is morphologically and functionally heterogeneous. This heterogeneity has stymied attempts to define functional properties of individual cell types and has led to controversy concerning mechanisms and regulation of ion transport. Recently, molecular techniques have been used to identify and localize ion transport pathways along the distal tubule and to identify human diseases that result from abnormal distal tubule function. Results of these studies have clarified the roles of individual distal cell types. They suggest that the basic molecular architecture of the distal nephron is surprisingly similar in mammalian species investigated to date. The results have also reemphasized the role played by the distal tubule in regulating urinary potassium excretion. They have clarified how both peptide and steroid hormones, including aldosterone and estrogen, regulate ion transport by distal convoluted tubule cells. Furthermore, they highlight the central role that the distal tubule plays in systemic calcium homeostasis. Disorders of distal nephron function, such as Gitelman's syndrome, nephrolithiasis, and adaptation to diuretic drug administration, emphasize the importance of this relatively short nephron segment to human physiology. This review integrates molecular and functional results to provide a contemporary picture of distal tubule function in mammals.

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With-No-Lysine Kinase 1 (WNK1) Augments TRPV4 Function in the Aldosterone-Sensitive Distal Nephron

Cells ◽

10.3390/cells10061482 ◽

2021 ◽

Vol 10 (6) ◽

pp. 1482

Author(s):

Viktor N. Tomilin ◽

Kyrylo Pyrshev ◽

Naghmeh Hassanzadeh Khayyat ◽

Oleg Zaika ◽

Oleh Pochynyuk

Keyword(s):

Collecting Duct ◽

Chinese Hamster ◽

Dominant Negative ◽

K Channel ◽

Apical Plasma Membrane ◽

Dependent Manner ◽

Distal Nephron ◽

Potassium Homeostasis ◽

Wnk Kinases ◽

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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Water permeability of apical and basolateral cell membranes of rat inner medullary collecting duct

AJP Renal Physiology ◽

10.1152/ajprenal.1990.259.6.f986 ◽

1990 ◽

Vol 259 (6) ◽

pp. F986-F999 ◽

Cited By ~ 5

Author(s):

B. Flamion ◽

K. R. Spring

Keyword(s):

Water Flow ◽

Water Permeability ◽

Cell Membranes ◽

Apical Membrane ◽

Collecting Duct ◽

Basolateral Membrane ◽

Volume Regulatory Decrease ◽

Water Permeation ◽

Inner Medullary Collecting Duct ◽

Medullary Collecting Duct

To quantify the pathways for water permeation through the kidney medulla, knowledge of the water permeability (Posmol) of individual cell membranes in inner medullary collecting duct (IMCD) is required. Therefore IMCD segments from the inner two thirds of inner medulla of Sprague-Dawley rats were perfused in vitro using a setup devised for rapid bath and luminal fluid exchanges (half time, t1/2, of 55 and 41 ms). Differential interference contrast microscopy, coupled to video recording, was used to measure volume and approximate surface areas of single cells. Volume and volume-to-surface area ratio of IMCD cells were strongly correlated with their position along the inner medullary axis. Transmembrane water flow (Jv) was measured in response to a variety of osmotic gradients (delta II) presented on either basolateral or luminal side of the cells. The linear relation between Jv and delta II yielded the cell membrane Posmol, which was then corrected for membrane infoldings. Basolateral membrane Posmol was 126 +/- 3 microns/s. Apical membrane Posmol rose from a basal value of 26 +/- 3 microns/s to 99 +/- 5 microns/s in presence of antidiuretic hormone (ADH). Because of amplification of basolateral membrane, the ADH-stimulated apical membrane remained rate-limiting for transcellular osmotic water flow, and the IMCD cell did not swell significantly. Calculated transcellular Posmol, expressed in terms of smooth luminal surface, was 64 microns/s without ADH and 207 microns/s with ADH. IMCD cells in anisosmotic media displayed almost complete volume regulatory decrease but only partial volume regulatory increase.

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