bluuebunny/crossref_metadata_2025 huggingface dataset:
Guanylin peptides: renal actions mediated by cyclic GMP
Authors: Forte Leonard R. , London Roslyn M. , Freeman Ronald H. , Krause William J.
Published: December 2017

The guanylin family of cGMP-regulating peptides has three subclasses of peptides containing either three intramolecular disulfides found in bacterial heat-stable enterotoxins (ST), or two disulfides observed in guanylin and uroguanylin, or a single disulfide exemplified by lymphoguanylin. These small, heat-stable peptides bind to and activate cell-surface receptors that have intrinsic guanylate cyclase (GC) activity. Two receptor GC signaling molecules have been identified that are highly expressed in the intestine (GC-C) and/or the kidney (OK-GC) and are selectively activated by the guanylin peptides. Stimulation of cGMP production in renal target cells by guanylin peptides in vivo or ex vivo elicits a long-lived diuresis, natriuresis, and kaliuresis. Activation of GC-C receptors in target cells of intestinal mucosa markedly stimulates the transepithelial secretion of Cl−and[Formula: see text], causing enhanced secretion of fluid and electrolytes into the intestinal lumen. Bacterial ST peptides act as mimics of guanylin and uroguanylin in the intestine, which provide a cellular mechanism underlying the diarrhea caused by ST-secreting strains of Escherichia coli. Uroguanylin and guanylin may participate in a novel endocrine axis linking the digestive system and kidney as a physiological mechanism that influences Na+homeostasis. Guanylin, uroguanylin, and/or lymphoguanylin may also serve within intrarenal signaling pathways controlling cGMP production in renal target cells. Thus we propose that guanylin regulatory peptides participate in a complex multifactorial biological process that evolved to regulate the urinary excretion of NaCl when dietary salt levels exceed the body's physiological requirements. This highly integrated and redundant mechanism allows the organism to maintain sodium balance by eliminating excess NaCl in the urine. Uroguanylin, in particular, may be a prototypical “intestinal natriuretic hormone.”
Protective effects of renal ischemic preconditioning and adenosine pretreatment: role of A1 and A3receptors
Authors: Lee H. Thomas , Emala Charles W.
Published: December 2017

Renal ischemia and reperfusion during aortic and renal transplant surgery result in ischemic-reperfusion injury. Ischemic preconditioning and adenosine infusion before ischemia protect against ischemic-reperfusion injury in cardiac and skeletal muscle, but these protective phenomena have not been demonstrated in the kidney. Rats were randomized to sham operation, 45-min renal ischemia, ischemic preconditioning with four cycles of 8-min renal ischemia and 5-min reperfusion followed by 45-min renal ischemia, systemic adenosine pretreatment before 45-min renal ischemia, or pretreatments with selective adenosine receptor subtype agonists or antagonists before 45-min renal ischemia. Forty-five minutes of renal ischemia followed by 24 h of reperfusion resulted in marked rises in blood urea nitrogen and creatinine. Ischemic preconditioning and adenosine pretreatment protected renal function and improved renal morphology. A1 adenosine receptor activation mimics and A1 adenosine antagonism blocks adenosine-induced protection. In addition, A3 adenosine receptor activation before renal ischemia worsens renal ischemic-reperfusion injury, and A3 adenosine receptor antagonism protects renal function. We demonstrate for the first time that rat kidneys can be preconditioned to attenuate ischemic-reperfusion injury and adenosine infusion before ischemic insult protects renal function via A1 adenosine receptor activation. Our data suggest that an A1 adenosine agonist and A3 adenosine antagonist may have clinically beneficial implications where renal ischemia is unavoidable.
Reabsorption of betaine in Henle's loops of rat kidney in vivo
Authors: Pummer Stefan , Dantzler William H. , Lien Yeong-Hau H. , Moeckel Gilbert W. , Völker Katharina , Silbernagl Stefan
Published: December 2017

This study was designed 1) to localize and 2) to characterize betaine reabsorption from the tubular lumen in rat kidney in vivo, and 3) to test whether reabsorption is modulated by the diuretic state. [14C]betaine (+ [3H]inulin) was microperfused through the proximal convoluted tubule (PCT) and microinfused into late proximal (LP) and early distal (ED) tubules, long loops of Henle (LLH), and vasa recta of the rat in vivo et situ, and the fractional recovery of the14C label was determined endproximally (PCT) and in the final urine, respectively. [14C]betaine was not reabsorbed during ED microinfusion, whereas fractional reabsorption during LP microinfusion was 82% at 0.06 mM betaine and decreased gradually to 4.8% at 60 mM. l-Proline had lower Michaelis-Menten constant ( Km) and sarcosine a higher Kmthan betaine. Chronic, but not acute, diuresis inhibited betaine reabsorption in Henle's loops. Fractional [14C]betaine reabsorption in PCT was much smaller than that during LP microinfusion. [14C]betaine (7.28 mM) microinfused 1) into LLH was reabsorbed to 30% and 2) into vasa recta appeared in the ipsilateral urine to a much higher extent than contralaterally. In both cases, no saturation was detected at 70 mM. We conclude that betaine is reabsorbed by mediated transport from descending limbs of short Henle's loops by a proline-preferring carrier in a diuresis-modulated manner. In the deep medulla, bidirectional blood/urine betaine transport exists.
Effects of insulin and atrial natriuretic peptide on renal tubular sodium handling in sickle cell disease
Authors: ter Maaten Jan C. , Serné Erik H. , van Eps Wim Statius , ter Wee Pieter M. , Donker Ab J. M. , Gans Rijk O. B.
Published: December 2017

We assessed the effect of insulin and atrial natriuretic peptide (ANP) on renal sodium handling in eight patients with sickle cell disease (SCD), who are characterized by loss of vasa recta and long loops of Henle, and matched control subjects. During insulin infusion (50 mU ⋅ kg−1⋅ h−1), fractional sodium excretion decreased by 0.44 ± 0.72% ( P = 0.13) in patients with SCD and by 0.57 ± 0.34% ( P = 0.002) in control subjects, whereas fractional distal sodium reabsorption increased by 4.1 ± 1.5% ( P < 0.001) and 3.0 ± 1.5% ( P < 0.001), respectively. Low-dose (0.3 pmol ⋅ kg−1⋅ h−1) ANP infusion did not affect renal sodium handling in patients with SCD but increased fractional sodium excretion by 0.34 ± 0.22% ( P= 0.003) in control subjects. High-dose (2 μg/min) ANP increased natriuresis to a similar extent in both groups. Insulin's antinatriuretic effects predominated over the natriuretic effects of low-dose, but not high-dose, ANP. These data suggest that insulin's antinatriuretic effect is localized at a distal tubular site other than the long loops of Henle and that the long loops are involved in the natriuretic effect of low-dose ANP, possibly mediated by changes in medullary blood flow.
Cell cycle regulatory proteins in renal disease: role in hypertrophy, proliferation, and apoptosis
Authors: Shankland Stuart J. , Wolf Gunter
Published: December 2017

The response to glomerular and tubulointerstitial cell injury in most forms of renal disease includes changes in cell number (proliferation and apoptosis) and cell size (hyerptrophy). These events typically precede and may be reponsible for the accumulation of extracellular matrix proteins that leads to a decrease in renal function. There is increasing evidence showing that positive (cyclins and cyclin-dependent kinases) and negative (cyclin-dependent kinase inhibitors) cell cycle regulatory proteins have a critical role in regulating these fundamental cellular responses to immune and nonimmune forms of injury. Data now show that altering specific cell cycle proteins affects renal cell proliferation and improves renal function. Equally exciting is the expanding body of literature showing novel biological roles for cell cycle proteins in the regulation of cell hypertrophy and apoptosis. With increasing understanding of the role for cell cyle regulatory proteins in renal disease comes the hope for potential therapeutic inverventions.
Localization of epithelial sodium channel and aquaporin-2 in rabbit kidney cortex
Authors: Loffing Johannes , Loffing-Cueni Dominique , Macher Andreas , Hebert Steven C. , Olson Beatriz , Knepper Mark A. , Rossier Bernard C. , Kaissling Brigitte
Published: December 2017

The amiloride-sensitive epithelial sodium channel (ENaC) and the vasopressin-dependent water channel aquaporin-2 (AQP2) mediate mineralocorticoid-regulated sodium- and vasopressin-regulated water reabsorption, respectively. Distributions of ENaC and AQP2 have been shown by immunohistochemistry in rats. Functional data from rabbits suggest a different distribution pattern of these channels than in rats. We studied, by immunohistochemistry in the rabbit kidney cortex, the distributions of ENaC and AQP2, in conjunction with marker proteins for distal segments. In rabbit cortex ENaC is restricted to the connecting tubule (CNT) cells and cortical collecting duct (CCD) cells. The intracellular distribution of ENaC shifts from the apical membrane in the most upstream CNT cells to a cytoplasmic location further downstream in the CNT and in the CCD cells. AQP2 is detected in the CCD cells exclusively. The anatomic subdivisions in the rabbit distal nephron coincide exactly with distributions of apical transport systems. The differences between rabbits and rats in the distribution patterns of ENaC and AQP2 may explain functional differences in renal salt and water handling between these species.
High dietary sodium chloride consumption may not induce body fluid retention in humans
Authors: Heer Martina , Baisch Friedhelm , Kropp Joachim , Gerzer Rupert , Drummer Christian
Published: December 2017

A commonly accepted hypothesis is that a chronically high-sodium diet expands extracellular volume and finally reaches a steady state where sodium intake and output are balanced whereas extracellular volume is expanded. However, in a recent study where the main purpose was to investigate the role of natriuretic peptides under day-to-day sodium intake conditions (Heer M, Drummer C, Baisch F, and Gerzer R. Pflügers Arch 425: 390–394, 1993), our laboratory observed increases in plasma volume without any rise in extracellular volume. To scrutinize these results that were observed as a side effect, we performed a controlled, randomized study including 32 healthy male test subjects in a metabolic ward. The NaCl intake ranged from a low level of 50 meq NaCl/day to 200, 400, and 550 meq/day, respectively. Plasma volume dose dependently increased ( P < 0.01), being elevated by 315 ± 37 ml in the 550-meq-NaCl-intake group. However, in contrast to the increased plasma volume, comparable to study I, total body water did not increase. In parallel, body mass also did not increase. Mean corpuscular volume of erythrocytes, as an index for intracellular volume, was also unchanged. We conclude from the results of these two independently conducted studies that under the chosen study conditions, in contrast to present opinions, high sodium intake does not induce total body water storage but induces a relative fluid shift from the interstitial into the intravascular space.
Maturation of proximal straight tubule NaCl transport: role of thyroid hormone
Authors: Shah Mehul , Quigley Raymond , Baum Michel
Published: December 2017

We have recently demonstrated that the rates of both active and passive proximal straight tubule (PST) NaCl transport in neonatal rabbits were less than in adults. In this segment NaCl entry across the apical membrane is via parallel Na+/H+ and Cl−/OH− exchangers, which increases in activity with maturation. The present in vitro microperfusion study examined whether thyroid hormone plays a role in the maturational increase in PST NaCl transport. Neonatal and adult PST were perfused with a high-chloride-low bicarbonate solution without organic solutes, simulating late proximal tubule fluid. Thyroid hormone-treated neonates had a higher rate of PST total and passive NaCl transport. In 8-wk-old animals that were hypothyroid since birth, the maturational increase in total and passive NaCl transport was prevented. Thyroid treatment for 4 days in hypothyroid 8-wk-old rabbits increased the rate of both total and passive NaCl transport. The maturational increases in both Na+/H+ and Cl−/OH− exchange activities were blunted in 8-wk-old hypothyroid animals and increased to control levels with thyroid treatment. This study demonstrates that thyroid hormone is a factor responsible for the maturational increase in both active and passive PST NaCl transport.
Long-term regulation of urea transporter expression by vasopressin in Brattleboro rats
Authors: Shayakul Chairat , Smith Craig P. , Mackenzie Harald S. , Lee Wen-Sen , Brown Dennis , Hediger Matthias A.
Published: December 2017

Regulation of urea concentration in the renal medullary interstitium is important for maintenance of hypertonicity and therefore the osmotic driving force for water reabsorption. Studies in Sprague-Dawley rats showed that restriction of water intake for 3 days results in upregulation of urea transporter (UT) mRNA in the inner stripe of outer medulla of the kidney (2.9-kb UT2) but not in the inner medulla (4.0-kb UT1). The present study was performed to investigate the role of vasopressin in long-term regulation of UT1 and UT2 in neurogenic diabetes insipidus (Brattleboro) rats treated with a 7-day continuous infusion of [Arg8]-vasopressin (AVP), [deamino-Cys1,d-Arg8]-vasopressin (dDAVP) or vehicle. Northern analysis showed that water restriction alone had no effect on the level of UT2 mRNA in vehicle-treated Brattleboro rats but UT2 mRNA markedly increased and UT1 mRNA modestly decreased after treatment with dDAVP. In situ hybridization further demonstrated that the UT2 signal is upregulated and spread along the descending thin limbs of loops of Henle and that UT1 signal is downregulated in the inner medullary collecting ducts in vasopressin-treated rats, with a greater response for dDAVP compared with the AVP-treated group. Immunocytochemistry studies revealed that the UT1 and UT2 proteins are also modified in the same pattern as the transcript changes. Our studies reveal the role of vasopressin in long-term regulation of UT1 and UT2 expression during water restriction.
Therapy with antisense TGF-β1 oligodeoxynucleotides reduces kidney weight and matrix mRNAs in diabetic mice
Authors: Han Dong Cheol , Hoffman Brenda B. , Hong Soon Won , Guo Jia , Ziyadeh Fuad N.
Published: December 2017

Inhibition of gene expression by antisense oligodeoxynucleotides (ODNs) relies on their ability to bind complementary mRNA sequences and prevent translation. The proximal tubule is a suitable target for ODN therapy in vivo because circulating ODNs accumulate in the proximal tubule in high concentrations. Because increased proximal tubular transforming growth factor- β1 (TGF-β1) expression may mediate diabetic renal hypertrophy, we investigated the effects of antisense TGF-β1 ODN on the high-glucose-induced proximal tubular epithelial cell hypertrophy in tissue culture and on diabetic renal hypertrophy in vivo. Mouse proximal tubular cells grown in 25 mM d-glucose and exposed to sense ODN as control (1 μM) exhibited increased3[H]leucine incorporation by 120% and total TGF-β1 protein by 50% vs. culture in 5.5 mM d-glucose. Antisense ODN significantly decreased the high-glucose-stimulated TGF-β1 secretion and leucine incorporation. Continuous infusion for 10 days of ODN (100 μg/day) was achieved via osmotic minipumps in diabetic and nondiabetic mice. Sense ODN-treated streptozotocin-diabetic mice had 15.3% increase in kidney weight, 70% increase in α1(IV) collagen and 46% increase in fibronectin mRNA levels compared with nondiabetic mice. Treatment of diabetic mice with antisense ODN partially but significantly decreased kidney TGF-β1 protein levels and attenuated the increase in kidney weight and the α1(IV) collagen and fibronectin mRNAs. In conclusion, therapy with antisense TGF-β1 ODN decreases TGF-β1 production and attenuates high-glucose-induced proximal tubular cell hypertrophy in vitro and partially prevents the increase in kidney weight and extracellular matrix expression in diabetic mice.
Rat homolog of sulfonylurea receptor 2B determines glibenclamide sensitivity of ROMK2 in Xenopus laevisoocyte
Authors: Tanemoto Masayuki , Vanoye Carlos G. , Dong Ke , Welch Richard , Abe Takaaki , Hebert Steven C. , Xu Jason Z.
Published: December 2017

Recent studies showed that coexpression of Kir6.1 or Kir6.2 with the sulfonylurea receptor (SUR1, SUR2A, or SUR2B) reconstituted an inwardly rectifying, ATP-sensitive K+channel that was inhibited by glibenclamide (2, 15–17). Here we report the isolation of a rat homolog of mouse SUR2B (denoted rSUR2B) from a rat kidney cDNA library. The rSUR2B sequence contains a 4,635-bp open reading frame that encodes a 1,545-amino acid polypeptide, showing 67% shared identity with SUR1 (a pancreatic β-cell isoform) and 98% with both SUR2A (a brain isoform) and SUR2B (a vascular smooth muscle isoform). Consistent with the predicted structures of other members of the ATP-binding cassette (ABC) superfamily, the sequence of rSUR2B contains 17 putative membrane-spanning segments. Also, predicted Walker A and B consensus binding motifs, present in other ABC members, are conserved in the rSUR2B sequence. RT-PCR revealed that rSUR2B is widely expressed in various rat tissues including brain, colon, heart, kidney, liver, skeletal muscle, and spleen. The intrarenal distribution of the rSUR2B transcript was investigated using RT-PCR and Southern blot of microdissected tubules. The rSUR2B transcript was detected in proximal tubule, cortical thick ascending limb, distal collecting tubule, cortical collecting duct, and outer medullary collecting duct, but not medullary thick ascending limb. This distal distribution overlaps with that of ROMK. Coexpression of rSUR2B with ROMK2 cRNA (in 1:10 ratio) in Xenopus laevis oocytes resulted in whole cell Ba2+-sensitive K+ currents that were inhibited by glibenclamide (50% inhibition with 0.2 mM glibenclamide). In contrast, rSUR2B did not confer significant glibenclamide sensitivity to oocytes coinjected with ROMK1 or ROMK3. The interaction between ROMK2 and rSUR2B was further studied by coimmunoprecipitation of in vitro translated rSUR2B and ROMK2. In agreement with the functional data, the rSUR2B protein was coimmunoprecipitated with ROMK2 in the ROMK2-rSUR2B cotranslated samples. Our data demonstrate that ROMK2, but not ROMK1 and ROMK3, can interact with rSUR2B to confer a sulfonylurea-sensitive K+ channel, implicating SUR proteins in forming and regulating renal ATP-sensitive K+ channels. The ROMK isoform specificity of glibenclamide effects suggests that the NH2 terminus of the ROMK protein mediates rSUR2B-ROMK2 interactions.
Etomoxir-induced PPARα-modulated enzymes protect during acute renal failure
Authors: Portilla Didier , Dai Gonghe , Peters Jeffrey M. , Gonzalez Frank J. , Crew Mark D. , Proia Alan D.
Published: December 2017

Regulation of fatty acid β-oxidation (FAO) represents an important mechanism for a sustained balance of energy production/utilization in kidney tissue. To examine the role of stimulated FAO during ischemia, Etomoxir (Eto), clofibrate, and WY-14,643 compounds were given 5 days prior to the induction of ischemia/reperfusion (I/R) injury. Compared with rats administered vehicle, Eto-, clofibrate-, and WY-treated rats had lower blood urea nitrogen and serum creatinines following I/R injury. Histological analysis confirmed a significant amelioration of acute tubular necrosis. I/R injury led to a threefold reduction of mRNA and protein levels of acyl CoA oxidase (AOX) and cytochrome P4A1, as well as twofold inhibition of their enzymatic activities. Eto treatment prevented the reduction of mRNA and protein levels and the inhibition of the enzymatic activities of these two peroxisome proliferator-activated receptor-α (PPARα) target genes during I/R injury. PPARα null mice subjected to I/R injury demonstrated significantly enhanced cortical necrosis and worse kidney function compared with wild-type controls. These results suggest that upregulation of PPARα-modulated FAO genes has an important role in the observed cytoprotection during I/R injury.
AGEs induce oxidative stress and activate protein kinase C-βIIin neonatal mesangial cells
Authors: Scivittaro Vincenzo , Ganz Michael B. , Weiss Miriam F.
Published: December 2017

Increased activation of specific protein kinase C (PKC) isoforms and increased nonenzymatic glycation of intracellular and extracellular proteins [the accumulation of advanced glycation end products (AGEs)] are major mechanistic pathways implicated in the pathogenesis of diabetic complications. Blocking PKC-βIIhas been shown to decrease albuminuria in animal models of diabetes. To demonstrate a direct relationship between AGEs and the induction and translocation of PKC-βII, studies were carried out in rat neonatal mesangial cells, known to express PKC-βIIin association with rapid proliferation in post-natal development. Oxidative stress was studied by using the fluorescent probe dichlorfluorescein diacetate. Translocation of PKC-βIIwas demonstrated by using immunofluorescence and Western blotting of fractionated mesangial cells. Induction of intracellular oxidative stress, increase in intracellular calcium, and cytosol to membrane PKC-βIItranslocation (with no change in PKC-α) were demonstrated after exposure to AGE-rich proteins. These data support the hypothesis that AGEs cause mesangial oxidative stress and alterations in PKC-βII, changes that may ultimately contribute to phenotypic abnormalities associated with diabetic nephropathy.
Mouse proximal tubular cell-cell adhesion inhibits apoptosis by a cadherin-dependent mechanism
Authors: Bergin Eoin , Levine Jerrold S. , Koh Jason S. , Lieberthal Wilfred
Published: December 2017

Adhesion of epithelial cells to matrix is known to inhibit apoptosis. However, the role of cell-cell adhesion in mediating cell survival remains uncertain. Primary cultures of mouse proximal tubular (MPT) cells were used to examine the role of cell-cell adhesion in promoting survival. When MPT cells were deprived of both cell-matrix and cell-cell adhesion, they died by apoptosis. However, when incubated in agarose-coated culture dishes (to prevent cell-matrix adhesion) and at high cell density (to allow cell-cell interactions), MPT cells adhered to one another and remained viable. Expression of E-cadherin among suspended, aggregating cells increased with time. A His-Ala-Val (HAV)-containing peptide that inhibits homophilic E-cadherin binding prevented cell-cell aggregation and promoted apoptosis of MPT cells in suspension. By contrast, inhibition of potential β1-integrin-mediated interactions between cells in suspension did not prevent either aggregation or survival of suspended cells. Aggregation of cells in suspension activated phosphatidylinositol 3-kinase (PI3K), an event that was markedly reduced by the presence of the HAV peptide. LY-294002, an inhibitor of PI3K, also inhibited survival of suspended cells. In summary, we provide novel evidence that MPT cells, when deprived of normal cell-matrix interactions, can adhere to one another in a cadherin-dependent fashion and remain viable. Survival of aggregated cells depends on activation of PI3K.
Roles of NO and oxygen radicals in tubuloglomerular feedback in SHR
Authors: Welch William J. , Tojo Akihiro , Wilcox Christopher S.
Published: December 2017

The spontaneously hypertensive rat (SHR) has enhanced tubuloglomerular feedback (TGF) responses and diminished buffering by juxtaglomerular apparatus (JGA)-derived nitric oxide (NO) despite enhanced expression of NO synthase (NOS) isoforms in the JGA. We tested the hypothesis that the enhanced TGF response is due to inactivation of NO by oxygen radicals ([Formula: see text]). SHR had significantly ( P< 0.05) greater expression of the peroxynitrate reaction product, nitrotyrosine, in renal cortex. A membrane-permeant, metal-independent superoxide dismutase mimetic, tempol, was used to test the functional role of [Formula: see text]. Maximum TGF responses, assessed from changes in proximal stop-flow pressure (PSF) during orthograde loop of Henle (LH) perfusion of artificial tubular fluid (ATF), were enhanced in SHR [Wistar-Kyoto rat (WKY) 8.8 ± 0.4 ( n = 30 nephrons) vs. SHR 10.8 ± 0.4 mmHg ( n = 39 nephrons), P < 0.001]. TGF responses of SHR were unresponsive to microperfusion of 7-nitroindazole (7-NI, 10−4M), which is an inhibitor of neuronal NOS (nNOS) [WKY 8.3 ± 0.3 to 10.8 ± 0.4 ( n = 8, P < 0.001) vs. SHR 10.0 ± 0.7 to 10.5 ± 0.8 mmHg ( n = 8; not significant)]. Microperfusion of tempol (10−4M) into the efferent arteriole (EA) supplying the peritubular capillaries (PTC) blunted TGF. The response to tempol was significantly ( P < 0.05) greater in SHR [ΔTGF in WKY 19 ± 6% ( n = 10) vs. SHR 32 ± 3% ( n = 10)]. Microperfusion of the NO donor compound S-nitroso- N-acetyl-penicillamine (SNAP, 10−7–10−4M) via the LH blunted TGF, but the sensitivity of the response was impaired significantly ( P < 0.05) in SHR nephrons. PTC perfusion of tempol (10−4M) normalized the response to loop perfusion of both SNAP and 7-NI in SHR nephron to levels in WKY (during tempol, ΔPSFwith 7-NI in WKY 8.9 ± 0.6 to 11.4 ± 0.8; n = 12 vs. SHR 9.5 ± 0.5 to 12.5 ± 0.4 mmHg; n = 16). In conclusion, TGF responses are enhanced in SHR, in part due to a diminished role for NO from nNOS in blunting TGF due to enhanced [Formula: see text]formation. [Formula: see text] in the JGA enhances TGF responses by inactivation of locally generated NO.
Luminal and contraluminal action of 1–34 and 3–34 PTH peptides on renal type IIa Na-Picotransporter
Authors: Traebert Martin , Völkl Harald , Biber Jürg , Murer Heini , Kaissling Brigitte
Published: December 2017

Parathyroid hormone (PTH) inhibits proximal tubular reabsorption of Piby retrieval of type IIa Na-Picotransporters (NaPi-IIa) from the brush-border membrane (BBM). We analyzed by immunohistochemistry whether PTH analogs, signaling through either protein kinase A (PKA) and C (PKC; 1–34 PTH) or only PKC (3–34 PTH), elicit in rat kidney in vivo or in the perfused murine proximal tubule in vitro a retrieval of NaPi-IIa and whether pharmacological agonists or inhibitors of these kinases are able to either mimic or interfere with these PTH effects. Treatment with either 1–34 or 3–34 PTH downregulated NaPi-IIa in rat kidney. In isolated murine proximal tubules 1–34 PTH was effective when added to either the apical or basolateral perfusate, whereas 3–34 PTH acted only via the luminal perfusate. These effects were mimicked by an activation of PKA with 8-bromoadenosine 3′,5′-cyclic monophosphate or PKC with 1,2-dioctanoylglycerol. The luminal action of both PTH peptides was blocked by inhibition of the PKC pathway (calphostin C), whereas the basolateral effect of 1–34 PTH was completely abolished by inhibiting both pathways (H-89 and calphostin C). These results suggest that 1) NaPi-IIa can be internalized by cAMP-dependent and -independent signaling mechanisms; 2) functional PTH receptors are located in both membrane domains; and 3) apical PTH receptors may preferentially initiate the effect through a PKC-dependent mechanism.
Glomerular hemodynamics in severe obesity
Authors: Chagnac Avry , Weinstein Talia , Korzets Asher , Ramadan Edward , Hirsch Judith , Gafter Uzi
Published: December 2017

Differential solute clearances were used to characterize glomerular function in 12 nondiabetic subjects with severe obesity (body mass index >38). Nine healthy subjects served as the control group. In the obese group, glomerular filtration rate (GFR) and renal plasma flow (RPF) exceeded the control value by 51 and 31%, respectively. Consequently, filtration fraction increased. The augmented RPF suggested a state of renal vasodilatation involving, mainly or solely, the afferent arteriole. Albumin excretion rate and fractional albumin clearance increased by 89 and 78%, respectively. Oral glucose tolerance tests were suggestive of insulin resistance. Insulin resistance was positively correlated with GFR ( r = 0.88, P < 0.001) and RPF ( r = 0.72, P < 0.001). Mean arterial pressure was higher than in the control group. Fractional clearances of dextrans of broad size distribution tended to be lowered. The determinants of the GFR were estimated qualitatively by using a theoretical model of dextran transport through a heteroporous membrane. This analysis suggests that the high GFR in very obese subjects may be the result of an increase in transcapillary hydraulic pressure difference (ΔP). An abnormal transmission of increased arterial pressure to the glomerular capillaries through a dilated afferent arteriole could account for the augmentation in ΔP.
Everything you wanted to know about the bladder epithelium but were afraid to ask
Authors: Lewis Simon A.
Published: December 2017

The mammalian urinary bladder epithelium (urothelium) performs the important function of storing urine for extended periods, while maintaining the urine composition similar to that delivered by the kidneys. The urothelium possesses four properties to perform this function. First, it offers a minimum epithelial surface area-to-urine volume; this reduces the surface area for passive movement of substances between lumen and blood. Second, the passive permeability of the apical membrane and tight junctions is very low to electrolytes and nonelectrolytes. Third, the urothelium has a hormonally regulated sodium absorptive system; thus passive movement of sodium from blood to urine is countered by active sodium reabsorption. Last, the permeability properties of the apical membrane and tight junctions of the urothelium are not altered by most substances found in the urine or blood. The importance of the barrier function of the urothelium is illustrated by infectious cystitis. The loss of the barrier function results in the movement of urinary constituents into the lamina propria and underlying muscle layers, resulting in suprapubic and lower back pain and frequent, urgent, and painful voiding.
Carbonic anhydrase IV is expressed in H+-secreting cells of rabbit kidney
Authors: Schwartz George J. , Kittelberger Ann M. , Barnhart Darlene A. , Vijayakumar Soundarapandian
Published: December 2017

Carbonic anhydrase (CA) IV is a membrane-bound enzyme that catalyzes the dehydration of carbonic acid to CO2and water. Using peptides from each end of the deduced rabbit CA IV amino acid sequence, we generated a goat anti-rabbit CA IV antibody, which was used for immunoblotting and immunohistochemical analysis. CA IV was expressed in a variety of organs including spleen, heart, lung, skeletal muscle, colon, and kidney. Rabbit kidney CA IV had two N-glycosylation sites and was sialated, the apparent molecular mass increasing by at least 11 to ∼45 kDa in the cortex. Medullary CA IV was much more heavily glycosylated than CA IV from cortex or any other organ, such modifications increasing the molecular mass by at least 20 kDa. CA IV was expressed on the apical and basolateral membranes of proximal tubules with expression levels on the order of S2 > S1 > S3 = 0. Because CA IV is believed to be anchored to the apical membrane by glycosylphosphatidylinositol, the presence of basolateral CA IV suggests an alternative mechanism. CA IV was localized on the apical membranes of outer medullary collecting duct cells of the inner stripe and inner medullary collecting duct cells, as well as on α-intercalated cells. However, CA IV was not expressed by β-intercalated cells, glomeruli, distal tubule, or Henle's loop cells. Thus CA IV was expressed by H+-secreting cells of the rabbit kidney, suggesting an important role for CA IV in urinary acidification.
Vascular endothelial growth factor is a survival factor for renal tubular epithelial cells
Authors: Kanellis John , Fraser Scott , Katerelos Marina , Power David A.
Published: December 2017

Vascular endothelial growth factor (VEGF) acts primarily as an endothelial cell mitogen via the “endothelial cell-specific” receptors VEGFR-1 (flt-1) and VEGFR-2 (flk-1/KDR). Only a few nonendothelial cells have been shown to possess functional VEGF receptors. We therefore examined the rat renal tubular epithelial cell line NRK52-E. NRK52-E expressed VEGFR-1 and VEGFR-2 mRNA and protein by RT-PCR, Northern blotting, Western blotting, immunofluorescence, and ligand binding. Serum-starved NRK52-E incubated with VEGF showed a significant increase in [3H]thymidine incorporation compared with control (2.3-fold at 1–10 ng/ml, P < 0.05; 3.3-fold at 50–100 ng/ml, P < 0.01). VEGF also protected NRK52-E from hydrogen peroxide-induced apoptosis and necrosis compared with control (annexin-V-FITC-positive cells, 39 vs. 54%; viable cells, 50.5 vs. 39.7%). Immunohistochemical staining using a variety of antibodies showed expression of both VEGF receptors in normal rat renal tubules in vivo. Because VEGF induced a proliferative and an antiapoptotic response in renal tubular epithelial cells, these data suggest that VEGF may act as a survival factor for renal tubular epithelium in vivo.
Upregulation of V1receptors in renal resistance vessels of rats developing genetic hypertension
Authors: Vågnes Øyvind , Feng Jian J. , Iversen Bjarne M. , Arendshorst William J.
Published: December 2017

Previous studies have demonstrated that arginine vasopressin (AVP) produces exaggerated renal vasoconstriction in young spontaneously hypertensive rats (SHR) relative to normotensive rats. The exaggerated renal vascular reactivity does not appear to be due to a primary defect in postreceptor calcium signal transduction. Although the magnitudes of vascular responses differ, the relative proportions of calcium entry and mobilization pathways evoked by AVP in renal resistance vessels are similar in these rat strains. The purpose of the present study was to evaluate possible differences in V1mRNA and receptor density and affinity in preglomerular resistance vessels (<50 μm) obtained from young Wistar-Kyoto (WKY) and SHR. Quantitative RT-PCR analysis revealed twofold greater expression of the V1areceptor gene in preglomerular arterioles of 7-wk-old SHR compared with WKY. In vitro radiolabeled ligand binding studies were performed under equilibrium conditions on preglomerular resistance arterioles freshly isolated from kidneys of 7-wk-old rats. The results indicate that AVP receptor density (Bmax) is two to three times greater in SHR than in WKY (248 ± 24 vs. 91 ± 11 fmol/mg protein, P < 0.001). The affinity does not differ between strains ( Kd= 0.5 nM). Displacement studies yielded similar results for SHR and WKY. Unlabeled AVP completely displaced [3H]AVP binding, with an IC50of 2.5 × 10−10M. Expression of AVP receptor types in afferent arterioles was evaluated using the V1receptor agonist, [Phe2, Ile3,Org8]vasopressin, the V1receptor antagonist, [d(CH2)5, Tyr(Me)2,Tyr(NH2)9]Arg8-vasopressin, and the V2receptor agonist, desamino-[d-Arg8]vasopressin. Both the V1agonist and antagonist displaced up to 90% of the AVP binding with IC50values of 4 × 10−8and 8 × 10−7M, respectively. The V2receptor agonist was a weak inhibitor, displacing less than 15% of AVP binding at a high concentration of 10−4M. These results demonstrate that virtually all AVP receptors in the preglomerular arterioles are of the V1type. Collectively, our results provide evidence that the enhanced renal reactivity to AVP is mediated by a higher density of V1receptors associated with increased gene expression in renal resistance vessels of SHR developing genetic hypertension.
Impaired myogenic autoregulation in kidneys of Brown Norway rats
Authors: Wang Xuemei , Ajikobi David O. , Salevsky Fred C. , Cupples William A.
Published: December 2017

The Brown Norway (BN) rat is normotensive and has an extended lifespan but is extremely sensitive to hypertension-induced renal injury. Relative impairment of autoregulation has been implicated in the progression of renal failure whereas absence of myogenic autoregulation is associated with early renal failure. Therefore, we tested the hypothesis that there is conditional failure of renal autoregulation in BN rats. In isoflurane-anesthetized BN rats, the pressure-flow transfer function was normal when pressure fluctuated spontaneously. External forcing increased pressure fluctuation and exposed weakness of the myogenic component of autoregulation; the component mediated by tubuloglomerular feedback was less affected. In the presence of vasopressin to raise renal perfusion pressure, myogenic autoregulation was further impaired during forcing in BN rats but not in Wistar rats. Compensation by the myogenic system was rapidly restored on cessation of forcing, suggesting a functional limitation rather than a structural failure. Graded forcing in Wistar rats and in spontaneously hypertensive rats revealed that compensation due to the myogenic system was strong and independent of forcing amplitude. In contrast, graded forcing in BN rats showed that compensation was reduced when fluctuation of blood pressure was increased but that the reduction was independent of forcing amplitude. The results demonstrate conditional failure of myogenic autoregulation in BN rats. These acute studies provide a possible explanation for the observed sensitivity to hypertension-induced renal injury in BN rats.
Specificity and functional analysis of the pH-responsive element within renal glutaminase mRNA
Authors: Laterza Omar F. , Curthoys Norman P.
Published: December 2017

The specificity and the functional significance of the binding of a specific cytosolic protein to a direct repeat of an eight-base AU sequence within the 3′-nontranslated region of the glutaminase (GA) mRNA were characterized. Competition experiments established that the protein that binds to this sequence is not an AUUUA binding protein. When expressed in LLC-PK1-F+cells, the half-life of a β-globin reporter construct, βG-phospho enolpyruvate carboxykinase, was only slightly affected (1.3-fold) by growth in acidic (pH 6.9, 10 mM [Formula: see text]) vs. normal (pH 7.4, 25 mM [Formula: see text]) medium. However, insertion of short segments of GA mRNA containing the direct repeat or a single eight-base AU sequence was sufficient to impart a fivefold pH-responsive stabilization to the chimeric mRNA. Furthermore, site-directed mutation of the direct repeat of the 8-base AU sequence in a βG-GA mRNA, which contains 956 bases of the 3′-nontranslated region of the GA mRNA, completely abolished the pH-responsive stabilization of the wild-type βG-GA mRNA. Thus either the direct repeat or a single eight-base AU sequence is both sufficient and necessary to create a functional pH-response element.
Purification, characterization, and localization of an ATP diphosphohydrolase in porcine kidney
Authors: Lemmens Raf , Kupers Luc , Sévigny Jean , Beaudoin Adrien R. , Grondin Gilles , Kittel Agnes , Waelkens Etienne , Vanduffel Luc
Published: December 2017

Membranes of pig kidney cortex tissue were solubilized in the presence of Triton X-100. Partial purification of ATP diphosphohydrolase (ATPDase) was achieved by successive chromatography on concanavalin A-Sepharose, Q-Sepharose Fast Flow, and 5′-AMP-Sepharose 4B. Monoclonal antibodies against ATPDase were generated. Further purification of the ATPDase was obtained by immunoaffinity chromatography with these monoclonal antibodies. NH2-terminal amino acid sequencing of the 78-kDa protein showed a sequence very homologous to mammalian CD39. The protein is highly glycosylated, with a nominal molecular mass of ∼57 kDa. The purified enzyme hydrolyzed di- and triphosphates of adenosine, guanosine, cytidine, uridine, inosine, and thymidine, but AMP and diadenosine polyphosphates could not serve as substrates. All enzyme activities were dependent on divalent cations and were partially inhibited by 10 mM sodium azide. The distribution of the enzyme in pig kidney cortex was examined immunohistochemically. The enzyme was found to be present in blood vessel walls of glomerular and peritubular capillaries.
Nitric oxide regulates renal cortical cyclooxygenase-2 expression
Authors: Cheng Hui-Fang , Wang Jun-Ling , Zhang Ming-Zhi , McKanna James. A. , Harris Raymond C.
Published: December 2017

We have previously shown that cyclooxygenase-2 (COX-2) is localized to the cortical thick ascending limb of the loop of Henle (cTALH)/macula densa of the rat kidney, and expression increases in response to low-salt diet and/or angiotensin-converting enzyme (ACE) inhibition. Because of the localization of neuronal nitric oxide synthase (nNOS) to macula densa and surrounding cTALH, the present study investigated the role of nitric oxide (NO) in the regulation of COX-2 expression. For in vivo studies, rats were fed a normal diet, low-salt diet or low-salt diet combined with the ACE inhibitor captopril. In each group, one-half of them were treated with the nNOS inhibitors 7-nitroinidazole (7-NI) or S-methyl-thiocitrulline. Both of these NOS inhibitors inhibited increases in COX-2 mRNA and immunoreactive protein in response to low salt and low salt+captopril. For in vitro studies, COX-2 expression was studied in primary cultures of rabbit cTALH cells immunodisssected with Tamm-Horsfall antibody. Basal COX-2 immunoreactivity expression was stimulated by S-nitroso- N-acetyl-penicillamine (SNAP), an NO donor, and intracellular cGMP concentration. The cultured cells expressed immunoreactive nNOS, and 7-NI inhibited basal COX-2 immunoreactivity expression, which could be partially overcome by cGMP. In summary, these studies indicate that NO is a mediator of increased renal cortical COX-2 expression seen in volume depletion and suggest important interactions between the NO and COX-2 systems in the regulation of arteriolar tone and the renin-angiotensin system by the macula densa.
Downregulation of aquaporin-2 and -3 in aging kidney is independent of V2vasopressin receptor
Authors: Preisser L. , Teillet L. , Aliotti S. , Gobin R. , Berthonaud V. , Chevalier J. , Corman B. , Verbavatz J.-M.
Published: December 2017

The mechanisms underlying age-related polyuria were investigated in 10- and 30-mo-old female WAG/Rij rats. Urinary volume and osmolality were 3.9 ± 0.3 ml/24 h and 2,511 ± 54 mosmol/kgH2O in adult rats and 12.8 ± 0.8 ml/24 h and 1,042 ± 44 mosmol/kgH2O in senescent animals. Vasopressin V2receptor mRNA did not significantly differ between 10 and 30 mo, and [3H]vasopressin binding sites in membrane papilla were reduced by 30%. The cAMP content of the papilla was unchanged with age, whereas papillary osmolality was significantly lowered in senescent animals. The expression of aquaporin-1 (AQP1) and -4 was mostly unaltered from 10 to 30 mo. In contrast, aquaporin-2 (AQP2) and -3 (AQP3) expression was downregulated by 80 and 50%, respectively, and AQP2 was markedly redistributed into the intracellular compartment, in inner medulla of senescent animals, but not in renal cortex. These results indicate that age-related polyuria is associated with a downregulation of AQP2 and AQP3 expression in the medullary collecting duct, which is independent of vasopressin-mediated cAMP accumulation.
Extracellular ATP increases [Ca2+]iin distal tubule cells. I. Evidence for a P2Y2 purinoceptor
Authors: Bidet Michel , De Renzis Guy , Martial Sonia , Rubera Isabelle , Tauc Michel , Poujeol Philippe
Published: December 2017

Experiments were performed to characterize the P2 purinoceptor subtype responsible for cytoplasmic calcium mobilization in cells from the initial part of rabbit distal convoluted tubule (DCT). Free calcium concentration was measured in a DCT cell line (DC1) with the probe fura 2. Both ATP and UTP increased cytosolic Ca2+concentration ([Ca2+]i; EC503 and 6 μM, respectively). The order of potency for nucleotide analogs was ATP = UTP > adenosine 5′- O-[thiotriphosphate] ≫ ADP > UDP, which is consistent with the pharmacology of the P2Y2 receptor subtype. The increased [Ca2+]iresponses to ATP and UTP were strongly inhibited by suramin. Pretreatment of cells with pertussis toxin (PTX) attenuated the action of both nucleotides. Inhibition of phospholipase C with U-73122 totally blocked the [Ca2+]iresponse to ATP. Thus ATP- and UTP-stimulated [Ca2+]imobilization in DC1 cells appears to be mediated via the activation of P2Y2 purinoceptors coupled to a G protein mechanism that is partially sensitive to PTX. Calcium flux measurements showed that lanthanum- and nifedipine-sensitive calcium channels are involved in the [Ca2+]iresponse to ATP.
Molecular chaperones in the kidney: distribution, putative roles, and regulation
Authors: Beck Franz-X. , Neuhofer Wolfgang , Müller Eva
Published: December 2017

Molecular chaperones are intracellular proteins that prevent inappropriate intra- and intermolecular interactions of polypetide chains. A specific group of highly conserved molecular chaperones are the heat shock proteins (HSPs), many of which are constitutively expressed but most of which are inducible by diverse (in some cases specific) stress factors. HSPs, either alone or in cooperation with “partner” chaperones, are involved in cellular processes as disparate as correct folding and assembly of proteins, transport of proteins to specific intracellular locations, protein degradation, and preservation and restructuring of the cytoskeleton. The characteristic distribution of individual HSPs in the kidney, and their response to different challenges, suggests that a number of HSPs may fulfill specific, kidney-related functions. HSP72 and the osmotic stress protein 94 (Osp94) appear to participate in the adaptation of medullary cells to high extracellular salt and urea concentrations; the small HSPs (HSP25/27 and crystallins) may be involved in the function of mesangial cells and podocytes and contribute to the volume-regulatory remodeling of the cytoskeleton in medullary cells during changes in extracellular tonicity. HSP90 contributes critically to the maturation of steroid hormone receptors and may thus be a critical determinant of the aldosterone sensitivity of specific renal epithelial cells. Certain HSPs are also induced in various pathological states of the kidney. The observation that the expression of individual HSPs in specific kidney diseases often displays characteristic time courses and intrarenal distribution patterns supports the idea that HSPs are involved in the recovery but possibly also in the initiation and/or maintenance phases of these disturbances.
Differential subcellular localization of ENaC subunits in mouse kidney in response to high- and low-Na diets
Authors: Loffing Johannes , Pietri Laurence , Aregger Fintan , Bloch-Faure May , Ziegler Urs , Meneton Pierre , Rossier Bernard C. , Kaissling Brigitte
Published: December 2017

Previous electrophysiological experiments on renal cortical collecting ducts indicated that dietary sodium intake and variations in aldosterone plasma levels regulate the abundance of functional epithelial Na channels (ENaC) in the apical plasma membrane. In mouse kidney we investigated by immunohistochemistry whether feeding for 3 wk a diet with high (3% Na) and low (0.05% Na) Na content influences the distribution pattern of ENaC. In mice of all experimental groups, ENaC was apparent in cells from the late portion of the distal convoluted tubule (DCT2) down to the medullary collecting duct (CD). In mice on a high-Na diet (plasma aldosterone: 40.8 ± 2.0 ng/dl), the α-subunit was undetectable, and the β- and γ-ENaC were detected in the cytoplasm, but not in the apical plasma membrane of the cells. In contrast, in mice on a low-Na diet (plasma aldosterone: 93.6 ± 9.3 ng/dl) all three ENaC subunits were displayed in the subapical cytoplasm and in the apical membrane of DCT2, connecting tubule (CNT), and, although less prominent, in cortical CD cells. Apical plasma membrane immunostaining progressively decreased along the cortical CD, simultaneously with increasing cytoplasmic staining for β- and γ-ENaC. Thus our data on mice adapted to moderately low and high Na intake suggest that regulation of ENaC function in vivo involves shifts of β- and γ-subunits from the cytoplasm to the apical plasma membrane and vice versa, respectively. The insertion of these subunits into the apical plasma membrane coincides with upregulation of the α-subunit and its insertion into the apical plasma membrane.