bluuebunny/crossref_metadata_2025 huggingface dataset:
A simple, nonradioactive method for evaluating single-nephron filtration rate using FITC-inulin
Authors: Lorenz John N. , Gruenstein Eric
Published: December 2017

The determination of inulin concentration in nanoliter fluid samples is fundamental to micropuncture investigations of renal function, and this is generally accomplished through the use of radioisotopes. We report here a simple and reliable alternative to the use of radioisotopes that employs FITC-labeled inulin. Samples containing FITC-inulin are stored between oil columns in constant-bore microcapillary tubes, which are then used as cuvettes to determine fluorescence on a microscope fluorometer. Standard curves were generated and found to be linear, with correlation coefficients ( R) exceeding 0.99 in every case. Although the fluorescence of FITC-inulin was found to be pH dependent, the pH and fluorescence of each 20- to 40-nl sample could be normalized by the addition of 1 nl of 0.5 M HEPES at pH 7.5. In mice prepared for standard micropuncture, simultaneous measurements of tubular fluid-to-plasma ratios (TF/P) using FITC-inulin and [125I]iothalamate were highly correlated (slope = 0.95, y-intercept = 0.01, R = 0.942), as were whole kidney measurements of glomerular filtration rate (GFR) (slope = 1.25, y-intercept = −53.5 μl/min, R = 0.99). Micropuncture determinations of late-proximal samples from mice before and after treatment with acetazolamide showed expected changes: TF/P of FITC-inulin decreased from 1.89 ± 0.07 to 1.48 ± 0.10; single-nephron GFR (SNGFR) decreased from 9.64 ± 1.1 to 6.65 ± 1.0 nl/min; and fractional fluid reabsorption decreased from 45.3 ± 1.9 to 26.8 ± 5.2%. Measurements of TF/P of FITC-inulin, volume, and SNGFR using this technique were stable for at least 2 wk when samples were stored in the dark at 4°C. These data demonstrate that this simple method for determining inulin clearance represents a viable and accurate alternative to radioactive methods. This approach has the added benefits of being relatively inexpensive and leaving the micropuncture sample intact.
Effect of AT2receptor blockade on the pathogenesis of renal fibrosis
Authors: Morrissey Jeremiah J. , Klahr Saulo
Published: December 2017

Cellular and molecular events contributing to tubulointerstitial fibrosis of the kidney during obstructive nephropathy are driven in large part through increased angiotensin II levels in the obstructed kidney. Angiotensin converting enzyme inhibition or AT1receptor antagonism have been shown to ameliorate the fibrosis of the kidney due to obstruction of the ureter. In this investigation, we determine the effects of the AT2receptor antagonist PD-123319 on pathophysiological events within the kidneys of rats with unilateral ureteral obstruction. Treatment with PD-123319 was found to exacerbate the increase in interstitial volume and collagen IV matrix score of the ureteral obstructed kidney. Monocyte/macrophage infiltration of the injured kidney was no different between treated and untreated animals. The AT2receptor antagonist did, however, inhibit apoptosis of tubular cells, α-smooth muscle actin expression within the interstitium, and p53 expression in the ureteral obstructed kidney. These results suggest that angiotensin II operating through the AT2receptor exerts an antifibrotic effect on the kidney during obstructive nephropathy in opposition to the profibrotic effects of angiotensin II operating through the AT1receptor.
Arginine vasopressin stimulates phosphorylation of aquaporin-2 in rat renal tissue
Authors: Nishimoto Goro , Zelenina Marina , Li Dailin , Yasui Masato , Aperia Anita , Nielsen Søren , Nairn Angus C.
Published: December 2017

Aquaporin-2 (AQP2), the protein that mediates arginine vasopressin (AVP)-regulated apical water transport in the renal collecting duct, possesses a single consensus phosphorylation site for cAMP-dependent protein kinase A (PKA) at Ser256. The aim of this study was to examine whether AVP, and other agents that increase cAMP levels, could stimulate the phosphorylation of AQP2 in intact rat renal tissue. Rat renal papillae were prelabeled with32P and incubated with vehicle or drugs, and then AQP2 was immunoprecipitated. Two polypeptides corresponding to nonglycosylated (29 kDa) and glycosylated (35–48 kDa) AQP2 were identified by SDS-PAGE. AVP caused a time- and dose-dependent increase in phosphorylation of both glycosylated and nonglycosylated AQP2. The threshold dose for a significant increase in phosphorylation was 10 pM, which corresponds to a physiological serum concentration of AVP. Maximal phosphorylation was reached within 1 min of AVP incubation. This effect on AQP2 phosphorylation was mimicked by the vasopressin (V2) agonist, 1-desamino-[8-d-arginine]vasopressin (DDAVP), or forskolin. Two-dimensional phosphopeptide mapping indicated that AVP and forskolin stimulated the phosphorylation of the same site in AQP2. Immunoblot analysis using a phosphorylation state-specific antiserum revealed an increase in phosphorylation of Ser256after incubation of papillae with AVP. The results indicate that AVP stimulates phosphorylation of AQP2 at Ser256via activation of PKA, supporting the idea that this is one of the first steps leading to increased water permeability in collecting duct cells.
Isoforms of the Na-K-2Cl cotransporter in murine TAL I. Molecular characterization and intrarenal localization
Authors: Mount David B. , Baekgaard Allan , Hall Amy E. , Plata Consuelo , Xu Jason , Beier David R. , Gamba Gerardo , Hebert Steven C.
Published: December 2017

We have identified several alternatively spliced cDNAs encoding mBSC1, an apical bumetanide-sensitive Na+-K+-2Cl−cotransporter from mouse kidney. Two full-length clones were isolated, designated C4 and C9, predicting proteins of 770 and 1,095 amino acids, respectively. The C4 isoforms are generated by utilization of an alternative polyadenylation site located within the intron between exons 16 and 17 of the mBSC1 gene on chromosome 2; the resultant transcripts predict a truncated COOH terminus ending in a unique 55 amino acid sequence. The predicted C4 and C9 COOH termini differ in the distribution of putative phosphorylation sites for both protein kinase A and C. Independent splicing events involve three previously described cassette exons, which are predicted to encode most of the second transmembrane domain. A total of six different isoforms are expressed, generated by the combinatorial association of three cassette exons and two alternative 3′ ends. C9-specific and C4-specific antibodies detect proteins of ∼150 and 120 kDa, respectively, in mouse kidney. Immunofluorescence and immunohistochemistry indicate expression of both COOH-terminal isoforms within the thick ascending limb of the loop of Henle (TAL). However, staining with the C4 antibody is more heterogeneous, with a decreased proportion of positive cells in the cortical TAL. Functional expression in Xenopus oocytes indicates a dominant negative function for C4 isoforms [companion study, C. Plata, D. B. Mount, V. Rubio, S. C. Hebert, and G. Gamba. Am. J. Physiol. 276 ( Renal Physiol. 45): F347–F358, 1999], and the differential expression of these isoforms may contribute to functional heterogeneity of Na+-K+-2Cl−cotransport in mouse TAL.
A novel p64-related Cl−channel: subcellular distribution and nephron segment-specific expression
Authors: Edwards John C.
Published: December 2017

Several closely related proteins that have been implicated as chloride channels of intracellular membranes have recently been described. We report here the molecular cloning and characterization of a new member of this family from human cells. On the basis of sequence similarity, we conclude that this new protein represents the human version of a previously described protein from rat brain named p64H1. The human version of p64H1 (huH1) is a 28.7-kDa protein that shows an apparent molecular mass of 31 kDa by SDS-PAGE. A single 4.5-kb message is detected on Northern blots and is present in all tissues probed. The protein is expressed in an intracellular vesicular pattern in Panc-1 cells that is distinct from the endoplasmic reticulum, fluid-phase endocytic, and transferrin-recycling compartments, but which does colocalize with caveolin. In human kidney, huH1 is highly expressed in a diffuse pattern in the apical domain of proximal tubule cells. huH1 is expressed less abundantly in a vesicular pattern in glomeruli and distal nephron.
Postnatal development of carbonic anhydrase IV expression in rabbit kidney
Authors: Schwartz George J. , Olson Jennifer , Kittelberger Ann M. , Matsumoto Tohru , Waheed Abdul , Sly William S.
Published: December 2017

Carbonic anhydrase (CA) IV activity facilitates renal acidification by catalyzing the dehydration of luminal carbonic acid. CA IV has been localized to the proximal tubules and medullary collecting ducts. Maturation of CA IV expression has been considered to be important in the development of renal acid excretion. The purpose of the present study was to determine the maturational expression of CA IV in rabbit kidney. A guinea pig polyclonal antibody to purified rabbit lung microsomal membrane CA IV was generated. Immunoblotting of membrane proteins after peptide- N-glycosidase F treatment revealed two N-glycosylation sites and reduction in size from ∼52 to 35 kDa; there appeared to be heavier glycosylation in the medulla. In membrane and total proteins from the kidney cortex, CA IV was 15–30% of the adult level during the first 2 wk of life but increased to mature levels by 5 wk of age. The maturational pattern in the cortex was confirmed by measuring SDS-resistant CA hydratase activity. In the medulla, both membrane and total proteins were generally less than one-fourth of the adult level of CA IV during the first 2 wk of life before reaching mature levels by 5 wk of age. Immunohistochemistry showed staining in proximal tubules (apical > basolateral), with maximal label in the S2 segment. CA IV also appeared on the apical membranes of a minority cell type of the cortical collecting duct, presumably the α-intercalated cell. Several labeled cells also appeared to be the process of being extruded from medullary collecting ducts of 1- to 2-wk rabbits. The antibody did not reliably detect medullary CA IV expression in sections from mature rabbits. These studies indicate that there is a substantial postnatal increase in expression of CA IV in the maturing kidney in both the cortex and medulla. The disappearance of intercalated cells in the maturing rabbit medullary collecting duct may be part of a normal renal developmental program as previously reported [J. Kim, J.-H. Cha, C. C. Tisher, and K. M. Madsen. Am. J. Physiol. 270 ( Renal Fluid Electrolyte Physiol. 39): F575–F592, 1996]. It is likely that the maturation of CA IV expression contributes to the increase in renal acidification observed early in postnatal life.
Modulation of renal tubular cell function by RGS3
Authors: Grüning W. , Arnould T. , Jochimsen F. , Sellin L. , Ananth S. , Kim E. , Walz G.
Published: December 2017

The recently discovered family of regulators of G protein signaling (RGS) accelerates the intrinsic GTPase activity of certain Gα subunits, thereby terminating G protein signaling. Particularly high mRNA levels of one family member, RGS3, are found in the adult kidney. To establish the temporal and spatial renal expression pattern of RGS3, a polyclonal antiserum was raised against the COOH terminus of RGS3. Staining of mouse renal tissue at different gestational stages revealed high levels of RGS3 within the developing and mature tubular epithelial cells. We tested whether RGS3 can modulate tubular migration, an important aspect of tubular development, in response to G protein-mediated signaling. Several mouse intermedullary collecting duct (mIMCD-3) cell lines were generated that expressed RGS3 under the control of an inducible promoter. Lysophosphatidic acid (LPA) is a potent chemoattractant that mediates its effects through heterotrimeric G proteins. We found that induction of RGS3 significantly reduced LPA-mediated cell migration in RGS3-expressing mIMCD-3 clones, whereas chemotaxis induced by hepatocyte growth factor remained unaffected by RGS3. Our findings suggest that RGS3 modulates tubular functions during renal development and in the adult kidney.
Apical proton secretion by the inner stripe of the outer medullary collecting duct
Authors: Weiner I. David , Frank Amy E. , Wingo Charles S. ,   (With the Technical Assistance of Wulf Sullivan)
Published: December 2017

The inner stripe of outer medullary collecting duct (OMCDis) is unique among collecting duct segments because both intercalated cells and principal cells secrete protons and reabsorb luminal bicarbonate. The current study characterized the mechanisms of OMCDisproton secretion. We used in vitro microperfusion, and we separately studied the principal cell and intercalated cell using differential uptake of the fluorescent, pH-sensitive dye, 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Both the principal cell and intercalated cell secreted protons, as identified as Na+/H+exchange-independent intracellular pH (pHi) recovery from an intracellular acid load. Two proton transport activities were identified in the principal cell; one was luminal potassium dependent and Sch-28080 sensitive and the other was luminal potassium independent and luminal bafilomycin A1sensitive. Thus the OMCDisprincipal cell expresses both apical H+-K+-ATPase and H+-ATPase activity. Intercalated cell Na+/H+exchange-independent pHirecovery was approximately twice that of the principal cell and was mediated by pharmacologically similar mechanisms. We conclude 1) the OMCDisprincipal cell may contribute to both luminal potassium reabsorption and urinary acidification, roles fundamentally different from those of the principal cell in the cortical collecting duct; and 2) the OMCDisintercalated cell proton transporters are functionally similar to those in the principal cell, raising the possibility that an H+-K+-ATPase similar to the one present in the principal cell may contribute to intercalated cell proton secretion.
In vivo PTH provokes apical NHE3 and NaPi2 redistribution and Na-K-ATPase inhibition
Authors: Zhang Yibin , Norian John M. , Magyar Clara E. , Holstein-Rathlou Niels-H. , Mircheff Austin K. , McDonough Alicia A.
Published: December 2017

The aim of this study was to test the hypothesis that in vivo administration of parathyroid hormone (PTH) provokes diuresis/natriuresis through redistribution of proximal tubule apical sodium cotransporters (NHE3 and NaPi2) to internal stores and inhibition of basolateral Na-K-ATPase activity and to determine whether the same cellular signals drive the changes in apical and basolateral transporters. PTH-(1–34) (20 U), which couples to adenylate cyclase (AC), phospholipase C (PLC), and phospholipase A2(PLA2), or [Nle8,18,Tyr34]PTH-(3–34) (10 U), which couples to PLC and PLA2but not AC, were given to anesthetized rats as an intravenous bolus followed by low-dose infusion (1 U ⋅ kg−1⋅ min−1for 1 h). Renal cortex membranes were fractionated on sorbitol density gradients. PTH-(1–34) increased urinary cAMP excretion 3-fold, urine output (V) 2.0 ± 0.1-fold, and lithium clearance (CLi) 2.8 ± 0.3-fold. With this diuresis/natriuresis, 25% of NHE3 and 18% of NaPi2 immunoreactivity redistributed from apical membranes to higher density fractions containing intracellular membrane markers, and basolateral Na-K-ATPase activity decreased 25%. [Nle8,18,Tyr34]PTH-(3–34) failed to increase V or CLior to provoke redistribution of NHE3 or NaPi2, but it did inhibit Na-K-ATPase activity 25%. We conclude that in vivo PTH stimulates natriuresis/diuresis associated with internalization of apical NHE3 and NaPi2 and inhibition of Na-K-ATPase activity, that cAMP-protein kinase A stimulation is necessary for the natriuresis/diuresis and NHE3 and NaPi2 internalization, and that Na-K-ATPase inhibition is not secondary to depressed apical Na+transport.
Tubuloglomerular feedback in ACE-deficient mice
Authors: Traynor Timothy , Yang Tianxin , Huang Yuning G. , Krege John H. , Briggs Josie P. , Smithies Oliver , Schnermann Jürgen
Published: December 2017

In these experiments, we used a strain of angiotensin converting enzyme (ACE) germline null mutant mice, generated by J. H. Krege and co-workers (J. H. Krege, S. W. M. John, L. L. Langenbach, J. B. Hodgin, J. R. Hagaman, E. S. Bachman, J. C. Jennette, D. A. O’Brien, and O. Smithies. Nature 375: 146–148, 1995), to examine the effect of chronic ACE deficiency on the magnitude of tubuloglomerular feedback (TGF) responses. The genotype was determined by PCR on DNA extracted from the tail and was verified after each experiment by assessment of the blood pressure response to an injection of ANG I. To assess TGF responsiveness, we determined the change in stop-flow pressure (PSF) caused by increasing NaCl concentration at the macula densa by using micropuncture techniques. When loop of Henle flow rate was increased from 0 to 40 nl/min, PSF fell from a mean of 42.3 ± 1.95 to 33.6 ± 2.09 mmHg ( n = 6, P = 0.005) in wild-type mice (+/+), fell from 40.6 ± 2.35 to 38.6 ± 1.93 mmHg in heterozygous (+/−) mice ( n = 7, P = 0.014), and did not change in homozygous ACE (−/−) mice [36.7 ± 2.02 mmHg vs. 36.4 ± 2.01 mmHg; n = 4, P = not significant (NS)]. During an infusion of ANG II at a dose that did not significantly elevate blood pressure (70 ng ⋅ kg−1 ⋅ min−1), TGF response magnitude (PSF 0 − PSF 40) increased from 6.5 ± 1.4 to 9.8 ± 1.19 mmHg in +/+ ( P = 0.006), from 1.14 ± 0.42 to 4.6 ± 1.3 mmHg in +/− ( P = 0.016), and from 0.42 ± 0.25 to 4.02 ± 1.06 in −/− mice ( P = 0.05). Absence of TGF responses in ACE null mutant mice and restoration of near-normal responses during an acute infusion of ANG II supports previous conclusions that ANG II is an essential component in the signal transmission pathway that links the macula densa with the glomerular vascular pole.
H+-K+-ATPases: regulation and role in pathophysiological states
Authors: Silver Randi B. , Soleimani Manoocher
Published: December 2017

Molecular cloning experiments have identified the existence of two H+-K+-ATPases (HKAs), colonic and gastric. Recent functional and molecular studies indicate the presence of both transporters in the kidney, which are presumed to mediate the exchange of intracellular H+for extracellular K+. On the basis of these studies, a picture is evolving that indicates differential regulation of HKAs at the molecular level in acid-base and electrolyte disorders. Of the two transporters, gastric HKA is expressed constitutively along the length of the collecting duct and is responsible for H+secretion and K+reabsorption under normal conditions and may be stimulated with acid-base perturbations and/or K+depletion. This regulation may be species specific. To date there are no data to indicate that the colonic HKA (HKAc) plays a role in H+secretion or K+reabsorption under normal conditions. However, HKAc shows adaptive regulation in pathophysiological conditions such as K+depletion, NaCl deficiency, and proximal renal tubular acidosis, suggesting an important role for this exchanger in potassium, [Formula: see text], and sodium (or chloride) reabsorption in disease states. The purpose of this review is to summarize recent functional and molecular studies on the regulation of HKAs in physiological and pathophysiological states. Possible signals responsible for regulation of HKAs in these conditions will be discussed. Furthermore, the role of these transporters in acid-base and electrolyte homeostasis will be evaluated in the context of genetically altered animals deficient in HKAc.
A kinetic model of the thiazide-sensitive Na-Cl cotransporter
Authors: Chang Hangil , Fujita Toshiro
Published: December 2017

The aim of this study was to construct a numerical model of the thiazide-sensitive Na-Cl cotransporter (TSC) that can predict kinetics of thiazide binding and substrate transport of TSC. We hypothesized that the mechanisms underlying these kinetic properties can be approximated by a state diagram in which the transporter has two binding sites, one for sodium and another for chloride and thiazide. On the basis of the state diagram, a system of linear equations that should be satisfied in the steady state was postulated. Numerical solution of these equations yielded model prediction of kinetics of thiazide binding and substrate transport. Rate constants, which determine transitional rates between states, were systematically adjusted to minimize a penalty function that was devised to quantitatively estimate the difference between model predictions and experimental results. With the resultant rate constants, the model could simulate the following experimental results: 1) dissociation constant of thiazide in the absence of sodium and chloride; 2) inhibitory effect of chloride on thiazide binding; 3) stimulatory effect of sodium on thiazide binding; 4) combined effects of sodium and chloride on thiazide binding; 5) dependence of sodium influx on extracellular sodium and chloride; and 6) inhibition of sodium influx by extracellular thiazide. We conclude that known kinetic properties of TSC can be predicted by a model which is based on a state diagram.
Regulation of cyclooxygenase-2 expression in renal medulla by tonicity in vivo and in vitro
Authors: Yang Tianxin , Schnermann Jurgen B. , Briggs Josephine P.
Published: December 2017

Renal medullary prostaglandins are believed to exert an important functional role in antagonizing vasopressin effects in dehydration. Studies were undertaken to determine the effect of hyperosmolality on cyclooxygenase (COX) isoform expression in the renal medulla. COX-1 and COX-2 mRNA and protein levels were determined by RT-PCR or Western blotting in Sprague-Dawley rats on varying water intakes, in Brattleboro rats and in Long-Evans controls. Over a wide range of urinary tonicity, COX-2 expression correlated closely with urine osmolality levels ( R = 0.872). COX-1 levels did not vary. Immunolocalization showed that the stimulation of COX-2 expression by dehydration occurred predominantly in the collecting duct. Hypertonicity caused by addition of NaCl produced a dose- and time-dependent stimulation of COX-2 expression in mIMCD-K2 cells as well as in MDCK cells. COX-1 was unaffected. In the same cell lines, mannitol, sucrose, and raffinose also had a stimulatory effect. The tonicity-stimulated COX-2 expression in mIMCD-K2 cells was almost completely blocked by a tyrosine kinase inhibitor, genistein at 100 μM. In MDCK cells transfected with a 2.7-kb COX-2 promoter and lacZ reporter construct, NaCl induced a twofold increase in β-galactosidase activity. Using mIMCD-K2 cells, hypertonic NaCl (600 mosmol/kgH2O for 24 h) induced a 33-fold increase in PGE2release determined by enzyme immunoassay, an effect completely blocked by 3 μM indomethacin or the COX-2-specific blocker N-(2-cyclohexy-4-nitrophenyl)methanesulfonamide (NS-398). We conclude that in inner medulla, COX-2 but not COX-1 is upregulated by hyperosmolality.
Involvement of PDGF in pressure-induced mesangial cell proliferation through PKC and tyrosine kinase pathways
Authors: Kato Hiroaki , Osajima Akihiko , Uezono Yasuhito , Okazaki Masahiro , Tsuda Yuki , Tanaka Hiroshi , Oishi Yosuke , Izumi Futoshi , Nakashima Yasuhide
Published: December 2017

In glomerular hypertension, mesangial cells (MC) are subjected to at least two physical forces: mechanical stretch and high transmural pressure. Increased transmural pressure, as well as mechanical stretch, promotes MC proliferation, which may enhance glomerulosclerosis. The exact mechanism of this effect is not fully understood. We examined the effects of transmural pressure alone on cell proliferation and DNA synthesis and investigated the role of platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF), candidates for mediation of glomerular diseases, in the pressure-induced events. Pressure was applied to cultured MC placed in a sealed chamber using compressed helium gas. Application of pressure resulted in a time-dependent (∼2 h) and pressure level-dependent (∼80 mmHg) increase in cell number (1.4-fold) and [3H]thymidine incorporation (2.7-fold). Pressure-induced DNA synthesis was significantly suppressed by inhibitors of phospholipase C (2-nitro-4-carboxyphenyl- N, N-diphenylcarbamate), protein kinase C [1-(5-isoquinolinylsulfonyl)-2-methylpiperazine and chelerythrine], or tyrosine kinases (genistein). Pressure caused a rapid but transient formation of inositol 1,4,5-trisphosphate, which was blocked by the phospholipase C inhibitor. Pressure also promoted a rapid increase in tyrosine kinase activity. Pressure increased mRNA levels of PDGF-B, with a peak at 6 h, but not those of PDGF-A or bFGF. Pressure-induced DNA synthesis was partially inhibited by a neutralizing anti-PDGF antibody but not by an antibody against bFGF or nonimmune IgG. Our results indicated that pressure by itself increases DNA synthesis and proliferation of cultured rat MC possibly through activation of protein kinase C and tyrosine kinases, and PDGF-B could be partially involved in these pathways.
Cloning and functional expression of the mouse epithelial sodium channel
Authors: Ahn Yoon J. , Brooker David R. , Kosari Farhad , Harte Brian J. , Li Jinqing , Mackler Scott A. , Kleyman Thomas R.
Published: December 2017

The epithelial sodium channel (ENaC) plays a major role in the transepithelial reabsorption of sodium in the renal cortical collecting duct, distal colon, and lung. ENaCs are formed by three structurally related subunits, termed α-, β-, and γENaC. We previously isolated and sequenced cDNAs encoding a portion of mouse α-, β-, and γENaC (α-, β-, and γmENaC). These cDNAs were used to screen an oligo-dT-primed mouse kidney cDNA library. Full-length βmENaC and partial-length α- and γmENaC clones were isolated. Full-length α- and γmENaC cDNAs were subsequently obtained by 5′-rapid amplification of cDNA ends (5′-RACE) PCR. Injection of mouse α-, β-, and γENaC cRNAs into Xenopus oocytes led to expression of amiloride-sensitive ( Ki= 103 nM), Na+-selective currents with a single-channel conductance of 4.7 pS. Northern blots revealed that α-, β-, and γmENaC were expressed in lung and kidney. Interestingly, αmENaC was detected in liver, although transcript sizes of 9.8 kb and 3.1 kb differed in size from the 3.2-kb message observed in other tissues. A partial cDNA clone was isolated from mouse liver by 5′-RACE PCR. Its sequence was found to be nearly identical to αmENaC. To begin to identify regions within αmENaC that might be important in assembly of the native heteroligomeric channel, a series of functional experiments were performed using a construct of αmENaC encoding the predicted cytoplasmic NH2terminus. Coinjection of wild-type α-, β-, and γmENaC with the intracellular NH2terminus of αmENaC abolished amiloride-sensitive currents in Xenopus oocytes, suggesting that the NH2terminus of αmENaC is involved in subunit assembly, and when present in a 10-fold excess, plays a dominant negative role in functional ENaC expression.
Polycystin-2 expression is developmentally regulated
Authors: Markowitz Glen S. , Cai Yiqiang , Li Li , Wu Guanqing , Ward Llewellyn C. , Somlo Stefan , D’Agati Vivette D.
Published: December 2017

PKD2 encodes a protein of unknown function that is mutated in 15% of autosomal dominant polycystic kidney disease (ADPKD) families. We used polyclonal antisera against PKD2 to examine the pattern of Pkd2 expression in staged mouse embryos. Staining for Pkd2 was documented as early as the 6th embryonic day ( day E6) in the embryonic ectoderm and endoderm. Low-intensity staining is seen in metanephric ureteric bud at day E12.5. By day E15.5, the adult pattern of expression is established with low level staining in proximal tubules and high level, basolateral staining in distal tubules. Pkd2 expression is first detected in the medullary collecting ducts at postnatal day 14. Outside of the kidney, Pkd2 expression is widely distributed in utero and more restricted postnatally. The greatest intensity of staining is seen in the fetal but not adult adrenal cortex and in red blood cell precursors. Expression also is seen in multiple endocrine organs, in cardiac, skeletal, and smooth muscle, and in multiple mesenchymal tissues. The diffuse distribution and early expression of Pkd2 suggest a fundamental developmental role. The persistent strong expression in adult kidney is consistent with a more organ-specific function in the maintenance of the mature metanephric tubule.
Role of Fas (CD95) in tubulointerstitial disease induced by unilateral ureteric obstruction
Authors: Hughes Jeremy , Johnson Richard J.
Published: December 2017

Murine renal tubular epithelial cells and interstitial fibroblasts may express both Fas (CD95) death receptor and Fas ligand and are vulnerable to Fas-mediated death in vitro. We therefore hypothesized that an absence of renal Fas may protect resident cells from undergoing apoptosis. We performed unilateral ureteric ligation [producing unilateral ureteral obstruction (UUO)] in 6-wk-old normal control mice and C57Bl6/ lpr mice, which express a nonfunctional Fas receptor. Obstructed kidneys were removed at days 3, 7, and 14 ( n= 6 per group). Tubular cell apoptosis at day 7 was significantly reduced in lpr mice [21.8 ± 5.8 vs. 45.7 ± 7.6 cells/10 high-power fields (hpf), P < 0.02]. Importantly, there was no difference in tubular cell proliferation between normal and lpr mice at any time point studied. Interestingly, double labeling with terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) and the proximal tubule-specific antibody Fx1A indicated that the absence of Fas reduced distal but not proximal tubular death at day 7. In addition, there was no difference in interstitial cell apoptosis or proliferation, suggesting that Fas does not play a significant role in interstitial cell death. Importantly, inflammatory macrophage infiltration and ultimate collagen I deposition was unchanged in lprmice. In conclusion, the absence of functional cell surface Fas in UUO provides distal tubular cells with partial protection from apoptosis but does not affect interstitial cell fate in this model of tubulointerstitial injury.
Endopeptidases (kininases) are able to hydrolyze kinins in tubular fluid along the rat nephron
Authors: Casarini D. E. , Boim M. A. , Stella R. C. R. , Schor N.
Published: December 2017

The activities of serine endopeptidase, prolyl endopeptidase and neutral endopeptidase were determined in tubular fluid collected from several portions of the rat nephron as well as in urine. The enzyme activities were measured by HPLC using bradykinin (BK) as substrate. Free residual peptides of BK obtained by the action of these enzymes on the locally produced BK were also determined. The endopeptidase activities were found to be present throughout the nephron. Equimolar fragments of BK were detected in the early proximal tubule (Arg1-Pro7, Phe8-Arg9, Arg1-Gly4, Phe5-Arg9, and BK), late proximal tubule (Arg1-Phe5, Arg1-Pro7, Gly4-Pro7, Gly4-Arg9, and BK), late distal tubule (Arg1-Gly4, Phe5-Arg9, Arg1-Phe5, Ser6-Arg9, Gly4-Arg9, BK, and [des-Arg9]BK) and urine (Phe8-Arg9, Phe5-Arg9, Arg1-Phe5, Ser6-Arg9, Arg1-Pro7, Gly4-Pro7, Gly4-Arg9, BK, and [des-Arg9]BK). Our data suggest that the endopeptidases and exopeptidases are secreted by the nephron. Early proximal tubules secrete angiotensin converting enzyme and neutral endopeptidase, differing from late distal tubules that produce prolyl endopeptidase, serine endopeptidase, carboxypeptidase, and also neutral endopeptidase. All enzymes detected along the rat nephron were found in the urine. The existence of endopeptidases and carboxypeptidase in the distal nephron may have a potential physiological role in the inactivation of the kinins formed by kallikrein in the kidney and also in the inactivation of additional peptides other than BK.
Modeling of P-glycoprotein-involved epithelial drug transport in MDCK cells
Authors: Ito Shinya , Woodland Cindy , Sarkadi Balázs , Hockmann Guido , Walker Scott E. , Koren Gideon
Published: December 2017

P-glycoprotein (P-gp) on the apical membranes of epithelial cells is known as a drug efflux pump. However, unclear is its integral quantitative role in the overall epithelial drug transfer, which also involves distinct diffusion processes in parallel and sequence. We used a simple three-compartment model to obtain kinetic parameters of each drug transfer mechanism, which can quantitatively describe the transport time courses of P-gp substrates, digoxin and vinblastine, across P-gp-expressing MDCK cell monolayers grown on permeable filters. Our results show that the model, which assumes a functionally single drug efflux pump in the apical membrane with diffusion across two membranes and intercellular junctions, is the least complex model with which to quantitatively reproduce the characteristics of the data. Interestingly, the model predicts that the MDCK apical membranes are less diffusion permeable than the basolateral membrane for both drugs and that the distribution volume of vinblastine is 10-fold higher than that of digoxin. Additional experiments verified these model predictions. The modeling approach is feasible to quantitatively describe overall kinetic picture of epithelial drug transport. Further model refinement is necessary to incorporate other modes of drug transport such as transcytosis. Also, whether P-gp solely accounts for the pump function in this model awaits more studies.
ERK activation by urea in the renal inner medullary mIMCD3 cell line
Authors: Yang Xiao-Yan , Zhang Zheng , Cohen David M.
Published: December 2017

Urea- and NaCl-inducible extracellular signal-regulated kinase (ERK) phosphorylation exhibited dissimilar kinetics. Among cell lines examined, the effect of urea was unique to mIMCD3 inner medullary collecting duct cells and MDCK cells. Urea-inducible ERK activation was ∼10-fold less sensitive to the MEK inhibitor, PD-98059, than was that of NaCl. This difference did not appear to be accounted for by differential activation of MEK isoforms. Interestingly, the inhibitor of p38 activation, SB-203580, abrogated the effect of both urea and NaCl upon both ERK and MEK activation; however, the former was much less sensitive to the inhibitor. Consistent with this observation, NaCl was much more effective than urea at inducing p38 phosphorylation. The effect of hypertonic stress (e.g., sorbitol 100 mM) could be blocked by appropriate medium dilution such that isotonicity was maintained. In marked contrast, the effect of hyperosmotic urea could not be blocked in this fashion, implying the absence of dependence upon cell volume. Together, these data suggest that cells of the renal inner medulla are potentially uniquely responsive to urea and that urea and hypertonic stressors induce ERK activation through distinct mechanisms.
MAPK activation determines renal epithelial cell survival during oxidative injury
Authors: di Mari John F. , Davis Roger , Safirstein Robert L.
Published: December 2017

Ischemia/reperfusion (I/R) injury induces both functional and morphological changes in the kidney. Necrosis, predominantly of the proximal tubule (PT), is the hallmark of this model of renal injury, whereas cells of the distal nephron survive, apparently intact. We examined whether differences in cellular outcome of the various regions of the nephron may be due to segmental variation in the activation of the mitogen-activated protein kinases (MAPKs) in response to I/R injury. Whereas c-Jun N-terminal kinase (JNK) is activated in both the cortex and inner stripe of the outer medulla, the extracellular regulated kinase (ERK) pathway is activated only in the inner stripe in which thick ascending limb (TAL) cells predominate. These studies are consistent with the notion that ERK activation is essential for survival. To test this hypothesis directly, we studied an in vitro system in which manipulation of these pathways and their effects on cellular survival could be examined. Oxidant injury was induced in mouse PT and TAL cells in culture by the catabolism of hypoxanthine by xanthine oxidase. PT cells were found to be more sensitive than TAL cells to oxidative stress as assessed by cell counting, light microscopy, propidium iodide uptake, and fluorescence-activated cell sorting (FACS) analysis. Immunoprecipitation/kinase analysis revealed that JNK activation occurred in both cell types, whereas ERK activation occurred only in TAL cells. We then examined the effect of PD-098059, a MAP kinase kinase (MEK)-1 inhibitor of the ERK pathway, on PT and TAL survival. In TAL cells, ERK inhibition reduced cell survival nearly fourfold ( P < 0.001) after oxidant exposure. In PT cells, activation of the ERK pathway by insulin-like growth factor I (IGF-I) increased survival by threefold ( P < 0.001), and this IGF-I-enhanced cell survival was inhibited by PD-098059. These results indicate that cell survival in the kidney after ischemia may be dependent on ERK activation, suggesting that this pathway may be a target for therapeutic treatment in I/R injury.
Amino acid fluxes in rat thin limb segments of Henle’s loop during in vitro microperfusion
Authors: Brokl Olga H. , Dantzler William H.
Published: December 2017

Amino acids are apparently recycled between loops of Henle and vasa recta in the rat papilla in vivo. To examine more closely papillary amino acid transport, we measured transepithelial fluxes ofl-[14C]alanine and [14C]taurine in thin limbs of Henle’s loops isolated from rat papilla and perfused in vitro. In descending thin limbs (DTL) in vitro, unidirectional bath-to-lumen fluxes tended to exceed unidirectional lumen-to-bath fluxes for both radiolabeled amino acids, although the difference was statistically significant only for taurine. In ascending thin limbs (ATL) in vitro, unidirectional lumen-to-bath fluxes tended to exceed unidirectional bath-to-lumen fluxes, although the difference was again statistically significant only for taurine. These results are compatible with apparent directional movements of amino acids in vivo. However, none of the unidirectional fluxes was saturable or inhibitable, an observation compatible with apparent reabsorption from the ATL in vivo but not compatible with apparent movement from vasa recta to DTL in vivo. There was no evidence of net active transepithelial transport when concentrations of radiolabeled amino acids were matched on both sides of perfused tubule segments. These data suggest that regulation of amino acid movement in vivo may involve the vasa recta, not the DTL of Henle’s loops. The data also suggest that transepithelial movement of amino acids in thin limbs of Henle’s loop may occur via a paracellular route.
Selective targeting of cyclooxygenase-2 reveals its role in renal medullary interstitial cell survival
Authors: Hao Chuan-Ming , Kömhoff Martin , Guan Youfei , Redha Reyadh , Breyer Matthew D.
Published: December 2017

Renal medullary interstitial cells (MICs) are a major site of cyclooxygenase (COX)-mediated PG synthesis. These studies examined the role of COX in MIC survival. Immunoblot and nuclease protection demonstrate that cultured MICs constitutively express COX2, with little constitutive COX1 expression. SC-58236, a COX2-selective inhibitor, but not SC-58560, a COX1 inhibitor, preferentially blocks PGE2synthesis in MICs. Transduction with a COX2 antisense adenovirus reduced MIC COX2 protein expression and also decreased PGE2production. Antisense downregulation of COX2 was associated with MIC death, whereas a control adenovirus was without effect. Similarly, the COX2-selective inhibitor SC-58236 (30 μM) and several nonselective COX-inhibiting nonsteroidal anti-inflammatory drugs (NSAIDs), including sulindac, ibuprofen, and indomethacin, all caused MIC death. In contrast, SC-58560, a COX1-selective inhibitor, was 100-fold less potent for inducing MIC death than its structural congener SC-58236. NSAID-induced MIC death was associated with DNA laddering and nuclear fragmentation, consistent with apoptosis. These results suggest that COX2 plays an important role in MIC survival. COX2 inhibition may contribute to NSAID-associated injury of the renal medulla.
Distribution of angiotensin AT1and AT2receptor subtypes in the rat kidney
Authors: Miyata Noriyuki , Park Frank , Li Xiao Feng , Cowley Allen W.
Published: December 2017

ANG II contributes importantly to the regulation of renal vascular resistance, glomerular filtration, and tubular epithelial transport, yet there remains a paucity of information regarding the localization of the ANG II type 1 and 2 (AT1and AT2) receptors within the rat kidney particularly within the vasculature. The present study was designed to localize the transcriptional and translational site(s) of AT1and AT2receptor (AT1R and AT2R, respectively) expression within the rat kidney. Using immunohistochemistry, we detected the AT1R translational sites throughout the kidney, with the strongest labeling found in the vasculature of the renal cortex and the proximal tubules of the outer medulla. The AT2R protein expression was found throughout the rat kidney, although there was little to no expression found in the glomerulus and medullary thick ascending limbs of Henle (TAL). Gene-specific primers were then designed to distinguish between the receptor subtypes within microdissected renal tubular and vascular segments using RT-PCR. AT1AR, AT1BR, and AT2R mRNA were found within the renal vasculature (afferent arterioles, arcuate artery, and outer medullary descending vasa recta). The mRNA for both the AT1R isoforms was also detected in the glomeruli and the renal tubules (proximal tubules, TAL, and collecting ducts); however, no AT2R mRNA was detected within the glomerulus and was inconsistently found within the medullary TAL (MTAL). Taken together, these data show that mRNA for the AT1R subtypes was located in all of the renal tubular and vascular segments. Evidence for AT2R mRNA was also found in all but two of the vascular and tubular segments, the MTAL, and the glomeruli. These results are consistent with the whole tissue immunohistochemically localized receptors.
Micropuncture analysis of single-nephron function in NHE3-deficient mice
Authors: Lorenz John N. , Schultheis Patrick J. , Traynor Timothy , Shull Gary E. , Schnermann Jürgen
Published: December 2017

The Na/H exchanger isoform 3 (NHE3) is expressed in the proximal tubule and thick ascending limb and contributes to the reabsorption of fluid and electrolytes in these segments. The contribution of NHE3 to fluid reabsorption was assessed by micropuncture in homozygous ( Nhe3−/−) and heterozygous ( Nhe3+/−) knockout mice, and in their wild-type (WT, Nhe3+/+) littermates. Arterial pressure was lower in the Nhe3−/−mice (89 ± 6 mmHg) compared with Nhe3+/+(118 ± 4) and Nhe3+/−(108 ± 5). Collections from proximal and distal tubules demonstrated that proximal fluid reabsorption was blunted in both Nhe3+/−and Nhe3−/−mice (WT, 4.2 ± 0.3; Nhe3+/−, 3.4 ± 0.2; and Nhe3−/−, 2.6 ± 0.3 nl/min; P < 0.05). However, distal delivery of fluid was not different among the three groups of mice (WT, 3.3 ± 0.4 nl/min; Nhe3+/−, 3.3 ± 0.2 nl/min; and Nhe3−/−, 3.0 ± 0.4 nl/min; P < 0.05). In Nhe3−/−mice, this compensation was largely attributable to decreased single-nephron glomerular filtration rate (SNGFR): 10.7 ± 0.9 nl/min in the Nhe3+/+vs. 6.6 ± 0.8 nl/min in the Nhe3−/−, measured distally. Proximal-distal SNGFR differences in Nhe3−/−mice indicated that much of the decrease in SNGFR was due to activation of tubuloglomerular feedback (TGF), and measurements of stop-flow pressure confirmed that TGF is intact in Nhe3−/−animals. In contrast to Nhe3−/−mice, normalization of early distal flow rate in Nhe3+/−mice was not related to decreased SNGFR (9.9 ± 0.7 nl/min), but rather, to increased fluid reabsorption in the loop segment ( Nhe3+/+, 2.6 ± 0.2; Nhe3+/−, 3.6 ± 0.5 nl/min). We conclude that NHE3 is a major Na/H exchanger isoform mediating Na+and fluid reabsorption in the proximal tubule. In animals with NHE3 deficiency, normalization of fluid delivery to the distal tubule is achieved through alterations in filtration rate and/or downstream transport processes.
Glutamate transporters in kidney and brain
Authors: Hediger Matthias A.
Published: December 2017

Glutamate transporters play important roles in the termination of excitatory neurotransmission and in providing cells with glutamate for metabolic purposes. In the kidney, glutamate transporters are involved in reabsorption of filtered acidic amino acids, regulation of ammonia and bicarbonate production, and protection of cells against osmotic stress.
Hepatocyte growth factor promotes renal epithelial cell survival by dual mechanisms
Authors: Liu Youhua
Published: December 2017

Hepatocyte growth factor (HGF) has been shown to protect renal epithelial cells against apoptosis. To define the mechanism by which HGF inhibits apoptosis, we investigated the effect of HGF on the phosphorylation and expression of the Bcl-2 family proteins. Using a human proximal tubular epithelial cell (HKC) line as a model, we demonstrated that constitutive expression of HGF conveyed marked resistance to apoptotic death induced by serum withdrawal. HGF induced rapid phosphorylation of Akt in HKC cells, which was immediately followed by phosphorylation and resultant inactivation of Bad, a pro-apoptotic member of the Bcl-2 family. Pretreatment of the HKC cells with 10 nM wortmannin completely abolished HGF-induced phosphorylation of Akt and Bad, suggesting that this pathway is dependent on phosphoinositide (PI) 3-kinase. Overexpression of Bad increased apoptotic death in wild-type HKC cells but not in HGF-producing H4 cells. Immunoblotting confirmed that the Bad protein over-expressed in H4 cells was fully phosphorylated at both Ser112and Ser136sites. Prolonged incubation of HKC cells with HGF also dramatically induced expression of Bcl-xL, an anti-apoptotic member of the Bcl-2 family. These results suggest that the anti-apoptotic effect of HGF in renal epithelial cells is mediated by dual mechanisms involving two distinct Bcl-2 family proteins. HGF triggers Bad phosphorylation via the PI 3-kinase/Akt pathway, thereby inactivating this pro-apoptotic protein, while simultaneously inducing expression of anti-apoptotic Bcl-xL.
Posttranscriptional regulation of the proximal tubule NaPi-II transporter in response to PTH and dietary Pi
Authors: Murer Heini , Forster Ian , Hernando Nati , Lambert Georg , Traebert Martin , Biber Jürg
Published: December 2017

The rate of proximal tubular reabsorption of phosphate (Pi) is a major determinant of Pihomeostasis. Deviations of the extracellular concentration of Piare corrected by many factors that control the activity of Na-Picotransport across the apical membrane. In this review, we describe the regulation of proximal tubule Pireabsorption via one particular Na-Picotransporter (the type IIa cotransporter) by parathyroid hormone (PTH) and dietary phosphate intake. Available data indicate that both factors determine the net amount of type IIa protein residing in the apical membrane. The resulting change in transport capacity is a function of both the rate of cotransporter insertion and internalization. The latter process is most likely regulated by PTH and dietary Piand is considered irreversible since internalized type IIa Na-Picotransporters are subsequently routed to the lysosomes for degradation.