scholarly journals Cleavage state of γENaC in mouse and rat kidney

2021 ◽  
Author(s):  
Gustavo Frindt ◽  
Shujie Shi ◽  
Thomas R Kleyman ◽  
Lawrence G Palmer
Keyword(s):  
Molecular Mass ◽  
Apical Membrane ◽  
Rat Kidney ◽  
Mouse Kidney ◽  
Apparent Molecular Mass ◽  
Na Channel ◽  
Extracellular Proteases ◽  
Salt Diet ◽  
Heterologous System ◽  
Membrane Bound

Extracellular proteases can activate the epithelial Na channel (ENaC) by cleavage of the g subunit. Here we investigate the cleavage state of the channel in the kidneys of mice and rats on a low-salt diet. We identified the cleaved species of channels expressed in FRT cells by co-expressing the apical-membrane bound protease CAP1 (prostasin). To compare the peptides produced in the heterologous system with those in the mouse kidney we treated both lysates with PNGaseF to remove N-linked glycosylation. The apparent molecular mass of the smallest C-terminal fragment of gENaC (52 kDa) was indistinguishable from that of the CAP1-induced species in FRT cells. Similar cleaved peptides were observed in total and cell surface fractions of rat kidney. This suggests that most of the subunits at the surface have been processed by extracellular proteases. This was confirmed using non-reducing gels, in which the N- and C-terminal fragments of gENaC are linked by a disulfide bond. Under these conditions the major cleaved form in rat kidney had an apparent molecular mass of 56 kDa, ~4 kDa lower than that of the full-length form, consistent with excision of a short peptide by two proteolytic events. We conclude that the most abundant gENaC species in the apical membrane of rat and mouse kidney on a low-Na diet is the twice-cleaved, presumably activated form.

scholarly journals Regulation of ENaC trafficking in rat kidney

2016 ◽  
Vol 147 (3) ◽  
pp. 217-227 ◽  
Author(s):  
Gustavo Frindt ◽  
Diego Gravotta ◽  
Lawrence G. Palmer
Keyword(s):  
Rat Kidney ◽  
Surface Expression ◽  
Na Channel ◽  
Salt Diet ◽  
Golgi Protein ◽  
Endocytic Compartments ◽  
Gradient Separation ◽  
Na Depletion ◽  
Epithelial Na Channel ◽  
Salt Homeostasis

The epithelial Na channel (ENaC) forms a pathway for Na+ reabsorption in the distal nephron, and regulation of these channels is essential for salt homeostasis. In the rat kidney, ENaC subunits reached the plasma membrane in both immature and fully processed forms, the latter defined by either endoglycosidase H–insensitive glycosylation or proteolytic cleavage. Animals adapted to a low-salt diet have increased ENaC surface expression that is specific for the mature forms of the subunit proteins and is similar (three- to fourfold) for α, β, and γENaC. Kidney membranes were fractionated using differential centrifugation, sucrose-gradient separation, and immunoabsorption. Endoplasmic reticulum membranes, isolated using an antibody against calnexin, expressed immature γENaC, and the content decreased with Na depletion. Golgi membranes, isolated with an antibody against the cis-Golgi protein GM130, expressed both immature and processed γENaC; Na depletion increased the content of processed γENaC in this fraction by 3.8-fold. An endosomal compartment isolated using an antibody against Rab11 contained both immature and processed γENaC; the content of processed subunit increased 2.4-fold with Na depletion. Finally, we assessed the content of γENaC in the late endocytic compartments indirectly using urinary exosomes. All of the γENaC in these exosomes was in the fully cleaved form, and its content increased by 4.5-fold with Na depletion. These results imply that stimulation of ENaC surface expression results at least in part from increased rates of formation of fully processed subunits in the Golgi and subsequent trafficking to the apical membrane.

Renal synthesis of atriopeptin-like protein in physiology and pathophysiology

1991 ◽  
Vol 260 (4) ◽  
pp. F602-F607 ◽  
Author(s):  
J. E. Greenwald ◽  
P. Needleman ◽  
M. R. Wilkins ◽  
G. F. Schreiner
Keyword(s):  
Amino Acid ◽  
Molecular Mass ◽  
Rat Kidney ◽  
Gel Filtration ◽  
Apparent Molecular Mass ◽  
Frozen Sections ◽  
Puromycin Aminonucleoside ◽  
Adult Rat ◽  
Major Form ◽  
Anatomic Localization

Atriopeptin is synthesized in mammalian atria as a 126-amino acid (14 kDa) prohormone, but it is secreted and circulates as a 28-amino acid (2.5 kDa) peptide. We have demonstrated the synthesis and secretion of an atriopeptin-like peptide in neonatal and adult rat kidney cell cultures. In this study, we evaluated the site of renal synthesis of this protein and its expression in normal rats and rats made nephrotic with puromycin aminonucleoside. The major form of atriopeptin in normal kidneys comigrated with an apparent molecular mass of 2.5 kDa assessed by gel filtration chromatography. However, the major form of this atriopeptin-like protein in nephrotic kidneys was determined to have an apparent molecular mass similar to the heart prohormone. No atriopeptin prohormone was detected in the plasma of nephrotic rats. Localization of this renal atriopeptin-like protein was accomplished by immunocytochemistry of rat kidney frozen sections. Using an antibody generated against either the COOH-terminal or NH3-terminal region of the cardiac atriopeptin prohormone, we detected specific immunostaining in the distal cortical nephron of the nephrotic kidney. This is the first report of the anatomic localization of a renal atriopeptin-like protein and its upregulation in nephrosis.

Immunolocalization of anion transporter Slc26a7 in mouse kidney

2006 ◽  
Vol 290 (4) ◽  
pp. F937-F945 ◽  
Author(s):  
Paul L. Dudas ◽  
SueAnn Mentone ◽  
Colin F. Greineder ◽  
Daniel Biemesderfer ◽  
Peter S. Aronson
Keyword(s):  
Proximal Tubule ◽  
Immunofluorescence Microscopy ◽  
Apical Membrane ◽  
Rat Kidney ◽  
Mouse Kidney ◽  
Membrane Transporters ◽  
Thick Ascending Limb ◽  
Base Exchange ◽  
Proximal Tubule Cells ◽  
Anion Transporter

Previous studies have indicated that a major fraction of the filtered Cl− is reabsorbed via apical membrane Cl−/base exchange in the proximal tubule. Recent studies in Slc26a6 null mice have suggested that this transporter mediates only a portion of proximal tubule Cl−/base exchange, raising the possibility that one or more unidentified apical membrane transporters may additionally contribute. Recent studies have identified Slc26a7 as another Cl−/base exchanger expressed in the kidney. We therefore generated Slc26a7-specific polyclonal and monoclonal antibodies to examine cellular and subcellular sites of expression in mouse kidney. The specificity of each antibody was verified by immunoblotting and immunofluorescence of COS-7 cells transiently transfected with mouse Slc26a7. Immunofluorescence microscopy of mouse kidney detected the expression of Slc26a7 subapically in proximal tubule cells, and on the basolateral surface of thick ascending limb cells. Similar staining patterns were demonstrated with two antibodies shown to react with different epitopes on Slc26a7. Immunolocalization of Slc26a7 to proximal tubule and thick ascending limb was also observed in rat kidney. We conclude that Slc26a7 is expressed in the proximal tubule and thick ascending limb of the loop of Henle, and it may therefore contribute to anion transport in these nephron segments.

scholarly journals Membrane-Bound Lytic Endotransglycosylase inEscherichia coli

1998 ◽  
Vol 180 (13) ◽  
pp. 3441-3447 ◽  
Author(s):  
Angelika R. Kraft ◽  
Markus F. Templin ◽  
Joachim-Volker Höltje
Keyword(s):  
Reaction Mechanism ◽  
Molecular Mass ◽  
Apparent Molecular Mass ◽  
Inescherichia Coli ◽  
E Coli ◽  
Lytic Transglycosylase ◽  
Membrane Bound ◽  
Murein Sacculus

ABSTRACT The gene for a novel endotype membrane-bound lytic transglycosylase, emtA, was mapped at 26.7 min of theE. coli chromosome. EmtA is a lipoprotein with an apparent molecular mass of 22 kDa. Overexpression of the emtA gene did not result in bacteriolysis in vivo, but the enzyme was shown to hydrolyze glycan strands isolated from murein by amidase treatment. The formation of tetra- and hexasaccharides, but no disaccharides, reflects the endospecificity of the enzyme. The products are characterized by the presence of 1,6-anhydromuramic acid, indicating a lytic transglycosylase reaction mechanism. EmtA may function as a formatting enzyme that trims the nascent murein strands produced by the murein synthesis machinery into proper sizes, or it may be involved in the formation of tightly controlled minor holes in the murein sacculus to facilitate the export of bulky compounds across the murein barrier.

Rat intestinal ceramidase: purification, properties, and physiological relevance

2004 ◽  
Vol 287 (4) ◽  
pp. G929-G937 ◽  
Author(s):  
Maria Olsson ◽  
Rui-Dong Duan ◽  
Lena Ohlsson ◽  
Åke Nilsson
Keyword(s):  
Molecular Mass ◽  
Bile Salts ◽  
Apical Membrane ◽  
Rat Kidney ◽  
Intestinal Lumen ◽  
Renal Tubular Cells ◽  
Physiological Relevance ◽  
Sodium Taurodeoxycholate ◽  
Pancreatic Proteases ◽  
Renal Tubular

Neutral ceramidase activity has previously been identified in the intestinal mucosa and gut lumen and postulated to be important in the digestion of sphingolipids. It is found throughout the intestine but has never been fully characterized. We have purified rat intestinal neutral ceramidase from an eluate obtained by perfusing the intestinal lumen with 0.9% NaCl and 3 mM sodium taurodeoxycholate. Using a combination of acetone precipitation and ion-exchange, hydrophobic-interaction, and gel chromatographies, we obtained a homogenous enzyme protein with a molecular mass of ∼116 kDa. The enzyme acts on both [14C]octanoyl- and [14C]palmitoyl-sphingosine in the presence of glycocholic and taurocholic acid and the bile salt analog 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate but is inhibited by 2 mM or more of other bile salts. It is a glycosylated protein stable to trypsin and chymotrypsin exposure, is not influenced by Ca2+, Mg2+, or Mn2+, and is inhibited by Zn2+ and Cu2+. Mass fragmentographic analysis identified 12 fragments covering 17.5% of the sequence for neutral/alkaline ceramidase 2 purified (Mitsutake S, Tani M, Okino N, Mori K, Ichinose S, Omori A, Iida H, Nakamura T, and Ito M. J Biol Chem 276: 26249–262459, 2001) from rat kidney and located in apical membrane of renal tubular cells. Intestinal and kidney ceramidases also have similar molecular mass and ion dependence. Intestinal ceramidase thus is a neutral ceramidase 2 released by bile salts and resistant to pancreatic proteases. It is well suited to metabolize ceramide formed from dietary and brush border sphingolipids to generate other bioactive sphingolipid messengers.

scholarly journals Human small intestinal angiotensin-converting enzyme: intracellular transport, secretion and glycosylation

1993 ◽  
Vol 296 (3) ◽  
pp. 607-615 ◽  
Author(s):  
H Y Naim
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Molecular Mass ◽  
Brush Border ◽  
Intracellular Transport ◽  
Apparent Molecular Mass ◽  
Intestinal Cells ◽  
Converting Enzyme ◽  
Human Biopsy ◽  
Membrane Bound ◽  
Small Intestinal

Human intestinal angiotensin-converting enzyme (ACE) exists in the brush-border membrane as a monomeric protein of apparent molecular mass 184 kDa. It is associated with the membrane via a hydrophobic segment and has a transmembrane orientation [Naim (1992) Biochem. J. 286, 451-457]. In addition to the membrane-bound form (ACEm), hydrophilic forms of ACE (ACEsec) can be identified in biosynthetically labelled intestinal cells. Thus the culture medium of biosynthetically labelled human biopsy samples contains an ACE molecule which has an apparent molecular mass similar to that of its membrane-bound counterpart. The secreted ACEsec forms follow a precursor/product relationship with the mature ACE molecule. The effect of the monomeric structure of ACE in its intracellular transport and secretion was investigated by pulse-chase experiments on human biopsy samples labelled with [35S]methionine. The results reveal 2-3-fold slower transport of ACE from the endoplasmic reticulum (ER) to the Golgi as compared with the homodimeric proteins dipeptidylpeptidase IV and aminopeptidase N. Further, the transport kinetics of ACE are comparable with those of human sucrase-isomaltase and human maltase-glucoamylase, two brush-border disaccharidases that do not form homodimers in the ER of human small-intestinal cells. These findings strongly suggest that homodimerization of brush-border proteins may influence the rate of transport of these proteins from the ER to the Golgi. The effect of glycosylation on the transport and secretion of ACE was investigated by utilizing several inhibitors of glycan processing. Here, secretion of ACE molecules continued to take place, albeit to a considerably lesser extent. In fact, approx. 2-fold less ACE molecules were secreted in the presence of inhibitors of ER glucosidases I and II and cis-Golgi mannosidase-I, suggesting that carbohydrate processing is important in the attainment of a transport-competent conformation.

scholarly journals Tissue kallikrein activation of the epithelial Na channel

2012 ◽  
Vol 303 (4) ◽  
pp. F540-F550 ◽  
Author(s):  
Ankit B. Patel ◽  
Julie Chao ◽  
Lawrence G. Palmer
Keyword(s):  
Molecular Mass ◽  
Serine Proteases ◽  
Collecting Duct ◽  
Wild Type Mouse ◽  
Apparent Molecular Mass ◽  
Na Channel ◽  
Tissue Kallikrein ◽  
Cortical Collecting Duct ◽  
Rat Urine ◽  
Connecting Tubule

Epithelial Na Channels (ENaC) are responsible for the apical entry of Na+ in a number of different epithelia including the renal connecting tubule and cortical collecting duct. Proteolytic cleavage of γ-ENaC by serine proteases, including trypsin, furin, elastase, and prostasin, has been shown to increase channel activity. Here, we investigate the ability of another serine protease, tissue kallikrein, to regulate ENaC. We show that excretion of tissue kallikrein, which is secreted into the lumen of the connecting tubule, is stimulated following 5 days of a high-K+ or low-Na+ diet in rats. Urinary proteins reconstituted in a low-Na buffer activated amiloride-sensitive currents ( INa) in ENaC-expressing oocytes, suggesting an endogenous urinary protease can activate ENaC. We next tested whether tissue kallikrein can directly cleave and activate ENaC. When rat ENaC-expressing oocytes were exposed to purified tissue kallikrein from rat urine (RTK), ENaC currents increased threefold in both the presence and absence of a soybean trypsin inhibitor (SBTI). RTK and trypsin both decreased the apparent molecular mass of cleaved cell-surface γ-ENaC, while immunodepleted RTK produced no shift in apparent molecular mass, demonstrating the specificity of the tissue kallikrein. A decreased effect of RTK on Xenopus ENaC, which has variations in the putative prostasin cleavage sites in γ-ENaC, suggests these sites are important in RTK activation of ENaC. Mutating the prostasin site in mouse γ-ENaC (γRKRK186QQQQ) abolished ENaC activation and cleavage by RTK while wild-type mouse ENaC was activated and cleaved similar to that of the rat. We conclude that tissue kallikrein can be a physiologically relevant regulator of ENaC activity.

scholarly journals Acute effects of aldosterone on the epithelial Na channel in rat kidney

2015 ◽  
Vol 308 (6) ◽  
pp. F572-F578 ◽  
Author(s):  
Gustavo Frindt ◽  
Lawrence G. Palmer
Keyword(s):  
Rat Kidney ◽  
Surface Protein ◽  
Early Response ◽  
Surface Expression ◽  
Na Channel ◽  
Channel Activity ◽  
Acute Effects ◽  
Chronic Stimulation ◽  
Epithelial Na Channels ◽  
Epithelial Na Channel

The acute effects of aldosterone administration on epithelial Na channels (ENaC) in rat kidney were examined using electrophysiology and immunodetection. Animals received a single injection of aldosterone (20 μg/kg body wt), which reduced Na excretion over the next 3 h. Channel activity was assessed in principal cells of cortical collecting ducts as amiloride-sensitive whole cell clamp current ( INa). INa averaged 100 pA/cell, 20–30% of that reported for the same preparation under conditions of chronic stimulation. INa was negligible in control animals that did not receive hormone. The acute physiological response correlated with changes in ENaC processing and trafficking. These effects included increases in the cleaved forms of α-ENaC and γ-ENaC, assessed by Western blot, and increases in the surface expression of β-ENaC and γ-ENaC measured after surface protein biotinylation. These changes were qualitatively and quantitatively similar to those of chronic stimulation. This suggests that altered trafficking to or from the apical membrane is an early response to the hormone and that later increases in channel activity require stimulation of channels residing at the surface.

Identification of an apical \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{Cl}^{-}{/}\mathrm{HCO}_{3}^{-}\) \end{document} exchanger in rat kidney proximal tubule

2003 ◽  
Vol 285 (3) ◽  
pp. C608-C617 ◽  
Author(s):  
Snezana Petrovic ◽  
Liyun Ma ◽  
Zhaohui Wang ◽  
Manoocher Soleimani
Keyword(s):  
Proximal Tubule ◽  
Apical Membrane ◽  
Rat Kidney ◽  
Proximal Tubules ◽  
Immunocytochemical Staining ◽  
Kidney Cortex ◽  
Rat Kidney Cortex ◽  
Kidney Proximal Tubule ◽  
Anion Transporter

SLC26A6 (or putative anion transporter 1, PAT1) is located on the apical membrane of mouse kidney proximal tubule and mediates [Formula: see text] exchange in in vitro expression systems. We hypothesized that PAT1 along with a [Formula: see text] exchange is present in apical membranes of rat kidney proximal tubules. Northern hybridizations indicated the exclusive expression of SLC26A6 (PAT1 or CFEX) in rat kidney cortex, and immunocytochemical staining localized SLC26A6 on the apical membrane of proximal tubules, with complete prevention of the labeling with the preadsorbed serum. To examine the functional presence of apical [Formula: see text] exchanger, proximal tubules were isolated, microperfused, loaded with the pH-sensitive dye BCPCF-AM, and examined by digital ratiometric imaging. The pH of the perfusate and bath was kept at 7.4. Buffering capacity was measured, and transport rates were calculated as equivalent base flux. The results showed that in the presence of basolateral DIDS (to inhibit [Formula: see text] cotransporter 1) and apical EIPA (to inhibit Na+/H+ exchanger 3), the magnitude of cell acidification in response to addition of luminal Cl– was ∼5.0-fold higher in the presence than in the absence of [Formula: see text]. The Cl–-dependent base transport was inhibited by ∼61% in the presence of 0.5 mM luminal DIDS. The presence of physiological concentrations of oxalate in the lumen (200 μM) did not affect the [Formula: see text] exchange activity. These results are consistent with the presence of SLC26A6 (PAT1) and [Formula: see text] exchanger activity in the apical membrane of rat kidney proximal tubule. We propose that SLC26A6 is likely responsible for the apical [Formula: see text] (and Cl–/OH–) exchanger activities in kidney proximal tubule.

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