bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of angiotensin in renal sympathetic activation in cirrhotic rats
Authors: Voigt Michael D. , Jones Susan Y. , DiBona Gerald F.
Published: December 2017

Central nervous system (CNS) renin-angiotensin activity influences the basal level of renal sympathetic nerve activity (RSNA) and its reflex regulation. The effect of type 1 angiotensin II (ANG II)-receptor antagonist treatment (losartan) on cardiac baroreflex regulation of RSNA and renal sodium handling was examined in rats with cirrhosis due to common bile duct ligation (CBDL). Basal levels of heart rate, mean arterial pressure (MAP), RSNA, and urinary sodium excretion were not affected by intracerebroventricular administration of either losartan or vehicle to CBDL rats. After acute intravenous isotonic saline loading (10% body wt) in vehicle-treated CBDL rats, MAP was unchanged and the decrease in RSNA seen in normal rats did not occur. However, in losartan-treated CBDL rats, there were significant concurrent but transient decreases in MAP (−20 ± 2 mmHg) and RSNA (−25 ± 3%). The natriuretic response to acute volume loading in losartan-treated CBDL rats was significantly less than that in vehicle-treated CBDL rats only at those time points where there were significant decreases in MAP. Antagonism of CNS ANG II type 1 receptors augments the renal sympathoinhibitory response to acute volume loading in CBDL. However, the natriuretic response to the acute volume loading is not improved, likely due to the strong antinatriuretic influence of the concomitant marked decrease in MAP (renal perfusion pressure) mediated by widespread sympathetic withdrawal from the systemic vasculature.
Altered expression of Na transporters NHE-3, NaPi-II, Na-K-ATPase, BSC-1, and TSC in CRF rat kidneys
Authors: Kwon Tae-Hwan , Frøkiaer Jørgen , Fernández-Llama Patricia , Maunsbach Arvid B. , Knepper Mark A. , Nielsen Søren
Published: December 2017

In chronic renal failure (CRF), reduction in renal mass leads to an increase in the filtration rates of the remaining nephrons and increased excretion of sodium per nephron. To address the mechanisms involved in the increased sodium excretion, we determined the total kidney levels and the densities per nephron of the major renal NaCl transporters in rats with experimental CRF. Two weeks after 5/6 nephrectomy (reducing the total number of nephrons to ∼24 ± 8%), the rats were azotemic and displayed increased Na excretion. Semiquantitative immunoblotting revealed significant reduction in the total kidney levels of the proximal tubule Na transporters NHE-3 (48% of control), NaPi-II (13%), and Na-K-ATPase (30%). However, the densities per nephron of NHE-3, NaPi-II, and Na-K-ATPase were not significantly altered in remnant kidneys, despite the extensive hypertrophy of remaining nephrons. Immunocytochemistry confirmed the reduction in NHE-3 and Na-K-ATPase labeling densities in the proximal tubule. In contrast, there was no significant reduction in the total kidney levels of the thick ascending limb and distal convoluted tubule NaCl transporters BSC-1 and TSC, respectively. This corresponded to a 3.6 and 2.5-fold increase in densities per nephron, respectively (confirmed by immunocytochemistry). In conclusion, in this rat CRF model: 1) increased fractional sodium excretion is associated with altered expression of proximal tubule Na transporter expression (NHE-3, NaPi-II, and Na-K-ATPase), consistent with glomerulotubular imbalance in the face of increased single-nephron glomerular filtration rate; and 2) compensatory increases in BSC-1 and TSC expression per nephron occur in distal segments.
Mechanism of proximal tubule bicarbonate absorption in NHE3 null mice
Authors: Wang Tong , Yang Chao-Ling , Abbiati Thecla , Schultheis Patrick J. , Shull Gary E. , Giebisch Gerhard , Aronson Peter S.
Published: December 2017

NHE3 is the predominant isoform responsible for apical membrane Na+/H+exchange in the proximal tubule. Deletion of NHE3 by gene targeting results in an NHE3−/−mouse with greatly reduced proximal tubule[Formula: see text] absorption compared with NHE3+/+animals (P. J. Schultheis, L. L. Clarke, P. Meneton, M. L. Miller, M. Soleimani, L. R. Gawenis, T. M. Riddle, J. J. Duffy, T. Doetschman, T. Wang, G. Giebisch, P. S. Aronson, J. N. Lorenz, and G. E. Shull. Nature Genet. 19: 282–285, 1998). The purpose of the present study was to evaluate the role of other acidification mechanisms in mediating the remaining component of proximal tubule [Formula: see text] reabsorption in NHE3−/−mice. Proximal tubule transport was studied by in situ microperfusion. Net rates of[Formula: see text] ( JHCO3) and fluid absorption ( Jv) were reduced by 54 and 63%, respectively, in NHE3 null mice compared with controls. Addition of 100 μM ethylisopropylamiloride (EIPA) to the luminal perfusate caused significant inhibition of JHCO3and Jvin NHE3+/+mice but failed to inhibit JHCO3or Jvin NHE3−/−mice, indicating lack of activity of NHE2 or other EIPA-sensitive NHE isoforms in the null mice. Addition of 1 μM bafilomycin caused a similar absolute decrement in JHCO3in wild-type and NHE3 null mice, indicating equivalent rates of[Formula: see text] absorption mediated by H+-ATPase. Addition of 10 μM Sch-28080 did not reduce JHCO3in either wild-type or NHE3 null mice, indicating lack of detectable H+-K+-ATPase activity in the proximal tubule. We conclude that, in the absence of NHE3, neither NHE2 nor any other EIPA-sensitive NHE isoform contributes to mediating [Formula: see text] reabsorption in the proximal tubule. A significant component of[Formula: see text] reabsorption in the proximal tubule is mediated by bafilomycin-sensitive H+-ATPase, but its activity is not significantly upregulated in NHE3 null mice.
Early aldosterone action: toward filling the gap between transcription and transport
Authors: Verrey François
Published: December 2017

The mineralocorticoid hormone aldosterone stimulates transcellular Na+reabsorption across target epithelia after a lag period of 20 to 60 min by first activating preexisting channels (epithelial sodium channels, ENaC) and pumps (Na-K-ATPase) and, subsequently, increasing the overall transport capacity of the cells. Both these early regulatory and late anabolic-type actions depend on the transcriptional regulation exerted by hormone-activated mineralocorticoid and/or glucocorticoid receptors (MR and/or GR). Starting at the transcriptional side of the aldosterone action, recent studies have identified the small G protein K-Ras2 and the kinase sgk as the first early aldosterone-induced gene products potentially regulating Na+transport. At the level of the Na+transport effectors, much knowledge about ENaC and Na-K-ATPase structure-function relationship and regulation has accumulated. However, the regulatory pathway(s) that link the transcriptional action of aldosterone to these Na+transport proteins is still to a large extent unknown. The available data suggest that the early regulatory action of aldosterone is pleiotropic, similarly to the late anabolic-type action. The early Na+transport stimulation would be mediated by the rapid induction of gene products belonging to the regulatory network that integrates the inputs of diverse pathways and finally controls the function of the Na+transport machinery.
LDL stimulates collagen mRNA synthesis in mesangial cells through induction of PKC and TGF-β expression
Authors: Lee Hyun Soon , Kim Bong Cho , Hong Hye Kyung , Kim Young Sook
Published: December 2017

Abnormal lipid accumulation in glomeruli could be implicated in the pathogenesis of glomerulosclerosis. Low-density lipoprotein (LDL) stimulates collagen mRNA expression in cultured human mesangial cells (HMC). To explore the possible molecular mechanisms by which LDL promotes collagen gene expression, we examined the effects of LDL on protein kinase C (PKC) activity and transforming growth factor-β (TGF-β) expression in relation to collagen gene regulation in HMC. LDL (200 μg/ml) induced an acute increase in PKC activity, particularly PKC-α and -δ, within 15 min, which decreased to control value at 2 h. LDL stimulated TGF-β1, and α1(I) and α1(IV) collagen mRNA expression within 30 min of incubation with HMC, and levels remained elevated until hour 4. LDL induced the secretion of TGF-β by HMC. This TGF-β was shown by CCL-64 mink lung cell assay to be, in part, bioactive. The stimulatory effects of LDL on collagen gene regulation in HMC were blocked by the inhibition of PKC using GF-109203X (GFX) or the downregulation of PKC using phorbol myristate acetate. Neutralizing antibody to TGF-β inhibited the increased collagen mRNA expression by HMC exposed to LDL. The downregulation or inhibition of PKC did not affect the stimulatory effect of LDL on TGF-β mRNA or protein expression. These results suggest that in HMC, LDL stimulates collagen mRNA expression through the rapid activation of PKC-α and -δ and transcriptional upregulation of TGF-β. Thus PKC and TGF-β may function as independent key signaling intermediaries in the pathway by which LDL upregulates collagen gene expression in HMC.
Attenuation of renal ischemia-reperfusion injury in inducible nitric oxide synthase knockout mice
Authors: Ling Hong , Edelstein Charles , Gengaro Patricia , Meng Xianhong , Lucia Scott , Knotek Mladen , Wangsiripaisan Adisorn , Shi Yeuxian , Schrier Robert
Published: December 2017

Renal ischemia-reperfusion (I/R) injury was investigated in inducible nitric oxide synthase (iNOS) knockout mice. After a 26-min bilateral renal pedicle clamp, serum creatinine concentrations (in mg/dl) in wild-type mice after a 24-h reperfusion were 0.25 ± 0.03 in sham-operated controls and 2.3 ± 0.38 in ischemic mice ( P < 0.01); after 48 h, concentrations (in mg/dl) were 0.25 ± 0.03 in controls and 2.0 ± 0.18 in ischemic mice ( P < 0.01). iNOS knockout mice demonstrated an attenuation of serum creatinine concentration after renal I/R injury. Serum creatinine concentrations (mg/dl) after a 24-h reperfusion were 2.3 ± 0.22 in wild-type ischemic and 1.21 ± 0.25 in iNOS knockout ischemic mice ( P < 0.05); after 48 h, concentrations were 2.0 ± 0.18 in wild-type ischemic and 0.96 ± 0.25 in iNOS knockout ischemic mice ( P< 0.01). Histological scoring of acute tubular necrosis in iNOS knockout mice was decreased compared with that in wild-type controls (0.88 ± 0.2 vs. 3.3 ± 0.3, P< 0.05). iNOS protein in the renal cortex of wild-type mice subjected to renal I/R injury was undetectable up to 48 h. However, a strong upregulation of heat shock protein 72 expression was observed in renal cortex of iNOS knockout mice under basal conditions. In conclusion, kidneys of iNOS knockout mice were protected against ischemic acute renal failure. This protective effect may be related to a compensatory upregulation of heat shock protein 72.
Reduced abundance of aquaporins in rats with bilateral ischemia-induced acute renal failure: prevention by α-MSH
Authors: Kwon Tae-Hwan , Frøkiaer Jørgen , Fernández-Llama Patricia , Knepper Mark A. , Nielsen Søren
Published: December 2017

We examined the effect of temporary renal ischemia (30 min or 60 min) and reperfusion (1 day or 5 days) on the expression of renal aquaporins (AQPs) and urinary concentration in rats with bilateral ischemia-induced acute renal failure (ARF). Next, we tested whether reducing ischemia/reperfusion (I/R) injury by treatment with α-melanocyte stimulating hormone (α-MSH) affects the expression of AQPs and urine output. Rats with ARF showed significant renal insufficiency, and urinary concentration was markedly impaired. In rats with mild ischemic injury (30 min), urine output increased significantly to a maximum at 48 h, and then nearly normalized within 5 days. Consistent with this, semiquantitative immunoblotting revealed that kidney AQP1 and AQP2 abundance was significantly decreased after 24 h to 30 ± 5% and 40 ± 11% ( n = 8) of controls ( n = 9), respectively ( P < 0.05). Five days after ischemia, AQP2 abundance was not significantly decreased and urine output was normalized. In contrast, severe ischemic injury (60 min) resulted in a marked reduction in urine output at 24 h, despite a significant decrease in urine osmolality and solute-free water reabsorption, TcH2O. AQP1 and AQP2 abundance was markedly decreased to 51 ± 5% and 31 ± 9% ( n = 10) of controls ( n = 8) at 24 h ( P < 0.05). After 5 days, the rats developed gradually severe polyuria and had very low AQP2 and AQP1 levels [11 ± 4% and 6 ± 2% ( n = 5) of controls ( n = 8), respectively; P < 0.05]. A similar reduction was observed for AQP3. The reduction in AQP expression in the proximal tubule and inner medullary collecting duct was confirmed by immunocytochemistry. Next, we found that intravenous α-MSH treatment of rats with ARF significantly reduced the ischemia-induced downregulation of renal AQPs and reduced the polyuria. In conclusion, the I/R injury is associated with markedly reduced expression of the collecting duct and proximal tubule AQPs, in association with an impairment of urinary concentration. Moreover, α-MSH treatment significantly prevented the reduction in expression of AQPs and renal functional defects. Thus decreased AQP expression is likely to contribute to the impairment in urinary concentration in the postischemic period.
Introduction: Glutamate transport, metabolism, and physiological responses
Authors: Hediger M. A. , Welbourne T. C.
Published: December 2017

The material covered in this set of articles was originally presented at Experimental Biology ’98, in San Francisco, CA, on April 20, 1998. Here, the participants recount important elements of current research on the role of glutamate transporter activity in cellular signaling, metabolism, and organ function. W. A. Fairman and S. G. Amara discuss the five subtypes of human excitatory amino acid transporters, with emphasis on the EAAT4 subtype. M. A. Hediger discusses the expression and action of EAAC1 subtype of the human excitatory amino acid transporter. I. Nissim provides an overview of the significant role of pH in regulating Gln/Glu metabolism in the kidney, liver, and brain. J. D. McGivan and B. Nicholson describe some characteristics of glutamate transport regulation with regard to a specific experimental model of the bovine renal epithelial cell line NBL-1. Finally, T. C. Welbourne and J. C. Matthews introduce the “functional unit” concept of glutamate transport and how this relates to both glutamine metabolism and paracellular permeability.
Real-time assessment of α-ketoglutarate effect on organic anion secretion in perfused rabbit proximal tubules
Authors: Shuprisha Apichai , Lynch Ronald M. , Wright Stephen H. , Dantzler William H.
Published: December 2017

To determine the quantitative roles of the basolateral and luminal Na+-dicarboxylate (Na-DC) cotransporters in establishing and maintaining the α-ketoglutarate (αKG) gradient required for renal tubular secretion of organic anions, we measured net steady-state transepithelial secretion of fluorescein (FL) in real time in isolated, perfused S2 segments of rabbit renal proximal tubules. Net “basal” FL secretion in the absence of exogenous αKG had a Ktof ∼4 μM and a maximal transepithelial secretion rate ( Jmax) of ∼380 fmol ⋅ min−1⋅ mm−1(where Ktis the FL concentration that produces one-half the Jmax). It could be almost completely inhibited by basolateral p-aminohippurate (PAH). Selective inhibition of the basolateral Na-DC cotransporter indicated that recycling via this transporter of αKG that had been exchanged for FL supports ∼25% of the “basal” FL secretion. Physiological αKG concentrations of 10 μM in the bath or 50 μM in the perfusate stimulated net secretion of FL by ∼30 or ∼20%, respectively. These data indicate that the basolateral Na-DC cotransporter supports ∼42% of the net FL secretion. The luminal and basolateral effects of physiological concentrations of αKG were additive, indicating that the combined function of the luminal and basolateral Na-DC cotransporters can support ∼50% of the net FL secretion. This apparently occurs by their establishing and maintaining ∼50% of the outwardly directed αKG gradient that is responsible for driving basolateral FL/αKG exchange. The remaining ∼50% would be maintained by metabolic production of αKG in the cells.
Nucleotides regulate NaCl transport in mIMCD-K2 cells via P2X and P2Y purinergic receptors
Authors: McCoy David E. , Taylor Amanda L. , Kudlow Brian A. , Karlson Katherine , Slattery Margaret J. , Schwiebert Lisa M. , Schwiebert Erik M. , Stanton Bruce A.
Published: December 2017

Extracellular nucleotides regulate NaCl transport in some epithelia. However, the effects of nucleotide agonists on NaCl transport in the renal inner medullary collecting duct (IMCD) are not known. The objective of this study was to determine whether ATP and related nucleotides regulate NaCl transport across mouse IMCD cell line (mIMCD-K2) epithelial monolayers and, if so, via what purinergic receptor subtypes. ATP and UTP inhibited Na+ absorption [measured via Na+ short-circuit current[Formula: see text])] and stimulated Cl− secretion [measured via Cl−short-circuit current ([Formula: see text])]. Using selective P2 agonists, we report that P2X and P2Y purinoceptors regulate [Formula: see text] and[Formula: see text]. By RT-PCR, two P2X receptor channels (P2X3, P2X4) and two P2Y G protein-coupled receptors (P2Y1, P2Y2) were identified. Functional localization of P2 purinoceptors suggest that [Formula: see text] is stimulated by apical membrane-resident P2Y purinoceptors and P2X receptor channels, whereas[Formula: see text] is inhibited by apical membrane-resident P2Y purinoceptors and P2X receptor channels. Together, we conclude that nucleotide agonists inhibit[Formula: see text] across mIMCD-K2 monolayers through interactions with P2X and P2Y purinoceptors expressed on the apical plasma membrane, whereas extracellular nucleotides stimulate [Formula: see text]through interactions with P2X and P2Y purinoceptors expressed on the apical plasma membrane.
Vasopressin stimulates sodium transport in A6 cells via a phosphatidylinositide 3-kinase-dependent pathway
Authors: Edinger R. S. , Rokaw M. D. , Johnson J. P.
Published: December 2017

The enzyme phosphatidylinositide 3-kinase (PI3K) phosphorylates the D-3 position of the inositol ring of inositol phospholipids and produces 3-phosphorylated inositides. These novel second messengers are thought to mediate diverse cellular signaling functions. The fungal metabolite wortmannin covalently binds to PI3K and selectively inhibits its activity. The role of PI3K in basal and hormone-stimulated transepithelial sodium transport was examined using this specific inhibitor. Wortmannin, 50 nM, did not affect basal, aldosterone-stimulated, or insulin-stimulated transport in A6 cells. Wortmannin completely inhibits vasopressin stimulation of transport in these cells. Vasopressin stimulates PI3K activity in A6 cells. Vasopressin stimulation of transport is also blocked by 5 μM LY-294002, a second inhibitor of PI3K. One-hour preincubation with wortmannin blocked vasopressin stimulation of protein kinase A activity in the cells. Sodium transport responses to exogenous cAMP and forskolin, which directly activates adenylate cyclase, were not affected by wortmannin. These results indicate that wortmannin inhibits vasopressin stimulation of Na+transport at a site proximal to activation of adenylate cyclase. The results suggest that PI3K may be involved in receptor activation by vasopressin.
Regulation of the renal Na-HCO3cotransporter. XI. Signal transduction underlying CO2stimulation
Authors: Ruiz Ofelia S. , Robey R. Brooks , Qiu Yi-Yong , Wang Long Jiang , Li Cheng Jin , Ma Jianfei , Arruda Jose A. L.
Published: December 2017

We have previously shown that CO2stimulation of the renal Na-HCO3cotransporter (NBC) activity is abrogated by general inhibitors of protein tyrosine kinases. The more selective inhibitor herbimycin also blocked this effect at concentrations known to preferentially inhibit Src family kinases (SFKs). We therefore examined a role for SFKs in CO2-stimulated NBC activity. To this end, we engineered OK cells to express the COOH-terminal Src kinase (Csk), a negative regulator of SFKs. CO2stimulated NBC activity normally in β-galactosidase-expressing and untransfected control cells. In contrast, Csk-expressing cells had normal baseline NBC activity that was not stimulated by CO2. CO2stimulation increased both total SFK activity and specific tyrosine phosphorylation of Src. The specific MEK1/2 inhibitor PD-98059 completely inhibited the CO2stimulation of NBC activity as well as the accompanying phosphorylation and activation of ERK1/2. Our data suggest the involvement of both SFKs, probably Src, and the “classic” MAPK pathway in mediating CO2-stimulated NBC activity in renal epithelial cells.
Ksp-cadherin gene promoter. I. Characterization and renal epithelial cell-specific activity
Authors: Whyte Dilys A. , Li Congyi , Thomson R. Brent , Nix Stacey L. , Zanjani Reza , Karp Sharon L. , Aronson Peter S. , Igarashi Peter
Published: December 2017

Kidney-specific cadherin (Ksp-cadherin, cadherin 16) is a novel, kidney-specific member of the cadherin superfamily that is expressed exclusively in the basolateral membrane of renal tubular epithelial cells. To characterize the Ksp-cadherin gene promoter, a λ bacteriophage clone containing 3.7 kb of the proximal 5′ flanking region of the mouse Ksp-cadherin gene was isolated. The transcription initiation site was mapped by RNase protection assays and 5′ rapid amplification of cDNA ends, and a 709-bp intron was identified within the 5′ untranslated region. The proximal 5′ flanking region was “TATA-less” but contained other consensus promoter elements including an initiator (Inr), GC boxes, and a CAAT box. Potential binding sites were identified for transcription factors that are involved in tissue-specific gene expression including activator protein-2 (AP-2), hepatocyte nuclear factor-3 (HNF-3), basic helix-loop-helix (bHLH) proteins, CCAAT/enhancer-binding protein (C/EBP), and GATA factors. Transfection of luciferase reporter plasmids containing 2.6 kb of the 5′ flanking region markedly increased luciferase activity in renal epithelial cells (MDCK and mIMCD-3) but not in mesenchymal cells (NIH 3T3 and MMR1). Deletion analysis identified an 82-bp region from −31 to −113 that was essential for promoter activity in transfected renal epithelial cells. Electrophoretic mobility-shift assays showed that mIMCD-3 cells contain nuclear proteins that bind to this region of the promoter. Mutational analysis showed that sequences within the HNF-3 consensus site and CAAT box were involved in protein binding and promoter activity. We conclude that the proximal 5′ flanking region of the mouse Ksp-cadherin gene contains an orientation-dependent promoter that is kidney epithelial cell specific. The region of the promoter from −113 to −31 is required for transcriptional activity and contains binding sites for nuclear proteins that are specifically expressed in renal epithelial cells.
JG cell expression and partial regulation of a human renin genomic transgene driven by a minimal renin promoter
Authors: Sinn Patrick L. , Zhang Xiaoji , Sigmund Curt D.
Published: December 2017

In the kidney, renin gene expression is exquisitely localized to the juxtaglomerular (JG) cells lining the afferent arteriole, having the capacity to regulate renin synthesis in response to a variety of physiological cues. We investigated human renin gene expression in transgenic mice containing a genomic construct driven by 149 bp of its proximal promoter to elucidate whether this was sufficient to confer JG-specific expression. Whereas human renin mRNA was permissively expressed in most tissues, the transgene was expressed mainly in JG cells in the kidney. Active human renin and human prorenin were found in the systemic circulation at levels consistent with previous transgenic models. Remarkably, two lines displayed an appropriate upregulation of transgene mRNA in response to angiotensin-converting enzyme inhibition, and two lines exhibited a downregulation of transgene mRNA in response to subpressor and pressor doses of ANG II. Our results suggest that 149 bp of the human renin proximal promoter, in a context of a genomic construct, are sufficient to confer human renin expression in renal JG cells and at least some aspects of appropriate regulation.
Inhibition of macula densa-stimulated renin secretion by pharmacological blockade of cyclooxygenase-2
Authors: Traynor Timothy R. , Smart Ann , Briggs Josephine P. , Schnermann Jurgen
Published: December 2017

Previous results from our laboratory have shown that in the isolated perfused juxtaglomerular apparatus, nonselective inhibitors of cyclooxygenase (COX) activity prevent the stimulation of renin secretion by a reduction in luminal NaCl concentration at the macula densa. The present studies were performed to examine which COX isoform is involved in NaCl-dependent renin secretion. In the absence of COX inhibitors, a reduction in luminal NaCl (from Na 141/Cl 120 mM to Na 26/Cl 7 mM) caused an increase in renin secretion rate from 4.5 ± 1.8 to 26.1 ± 7.4 nGU/min ( P < 0.01, n = 19). The presence of the COX-1 inhibitor valerylsalicylate (500 μM) in lumen and bath did not affect the stimulation of renin secretion by a reduction in luminal NaCl concentration (5 ± 1.8 nGU/min at high NaCl, and 30.5 ± 9.4 nGU/min at low NaCl; P < 0.01, n = 8). In contrast, the specific COX-2 inhibitor NS-398 (50 μM) in lumen and bath abolished the stimulating effect of low luminal NaCl (12.8 ± 3.9 nGU/min at high NaCl, and 10.7 ± 3.1 nGU/min at low NaCl; NS, n = 15). The finding that COX-2 is critically involved in macula densa control of renin secretion indicates that the COX-2-expressing epithelial cells in the tubuloglomerular contact area are a likely source of prostaglandins participating in the signaling pathway between the macula densa and renin-producing granular cells.
Functional analysis of aquaporin-2 mutants associated with nephrogenic diabetes insipidus by yeast expression
Authors: Shinbo Itsuki , Fushimi Kiyohide , Kasahara Michihiro , Yamauchi Kazushi , Sasaki Sei , Marumo Fumiaki
Published: December 2017

Mutations of aquaporin-2 (AQP2) vasopressin water channel cause nephrogenic diabetes insipidus (NDI). It has been suggested that impaired routing of AQP2 mutants to the plasma membrane causes the disease; however, no determinations have been made of mutation-induced alterations of AQP2 channel water permeability. To address this issue, a series of AQP2 mutants were expressed in yeast, and the osmotic water permeability ( Pf) of the isolated vesicles was measured. Wild-type and mutant AQP2 were expressed equally well in vesicles. Pfof the vesicles containing wild-type AQP2 was 22 times greater than that of the control, which was sensitive to mercury and weakly dependent on the temperature. Pfmeasurements and mercury inhibition examinations suggested that mutants L22V and P262L are fully functional, whereas mutants N68S, R187C, and S216P are partially functional. In contrast, mutants N123D, T125M, T126M, A147T, and C181W had very low water permeability. Our results suggest that the structure between the third and fifth hydrophilic loops is critical for the functional integrity of the AQP2 water channel and that disruption of AQP2 water permeability by mutations may cause NDI.
Regulation by PKC isoforms of Na+/H+exchanger in luminal membrane vesicles isolated from cortical tubules
Authors: Karim Z. G. , Chambrey R. , Chalumeau C. , Defontaine N. , Warnock D. G. , Paillard M. , Poggioli J.
Published: December 2017

The present study was designed to determine the Na/H exchanger isoforms present in luminal membrane vesicles (LMV) isolated from rat kidney cortical tubule suspensions, as well as the effects of acute phorbol ester (phorbol myristate acetate, PMA) and angiotensin II (ANG II) pretreatment of suspensions on NHE activity and protein kinase C (PKC) isoform abundance. In LMV, both NHE3 and NHE2 proteins were found by Western blot analysis, but only ethylisopropylamiloride-sensitive and almost completely Hoe-694-resistant Na/H exchange activity was observed from22Na uptake and thus attributed to NHE3. PMA pretreatment increased Na/H exchange activity and PKC isoforms α, δ, and ε abundance in LMV, and these effects were prevented by PKC inhibition. Low-dose ANG II (10−11M) pretreatment increased Na/H exchange activity and only PKC-ζ abundance in LMV, and these effects were also prevented by PKC inhibition. After high-dose ANG II (10−7M), Na/H exchange activity was decreased in LMV. PKC inhibition did not prevent this effect. In conclusion, the stimulating effects of PMA and low-dose ANG II are explained by the translocation of different isoforms of PKC in LMV, whereas the inhibitory effect of high-dose ANG II is not PKC dependent.
Potassium secretion and the regulation of distal nephron K channels
Authors: Palmer Lawrence G.
Published: December 2017

K-selective channels in the luminal membranes of distal nephron segments form a key pathway for the secretion of K ions into the urine. This process is important to the control of K balance, particularly under conditions of normal or high K intake. This brief review will cover three issues: 1) the identification of apical K channels, 2) the role of these channels in the maintenance of K homeostasis, and 3) the role of aldosterone in this regulatory process. The large amount of literature on renal K transport has been elegantly summarized in a recent review in this journal [G. Giebisch. Am. J. Physiol.274 ( Renal Physiol. 43): F817–F833, 1998]. Here I will focus on a few prominent unsolved problems.
Regulation of the ROMK channel: interaction of the ROMK with associate proteins
Authors: Wang Wenhui
Published: December 2017

The ROMK channel plays an important role in K recycling in the thick ascending limb (TAL) and K secretion in the cortical collecting duct (CCD). A large body of evidence indicates that the ROMK channel is a key component of the native K secretory channel identified in the apical membrane of the TAL and the CCD. Although the ROMK channel shares several key regulatory mechanisms with the native K secretory channel in a variety of respects, differences in the channel modulatory mechanism are clearly present between the ROMK channel and the native K secretory channel. Therefore, it is possible that additional associate proteins are required to interact with the ROMK channel to assemble the native K secretory channel. This notion is supported by recent reports showing that cystic fibrosis transmembrane conductance regulator (CFTR) and A kinase anchoring proteins (AKAP) interact with the ROMK channels to restore the response to ATP sensitivity and protein kinase A stimulation. This review is an attempt to summarize the up-to-date progress regarding the interaction between the ROMK channel and the associate proteins in forming the native K secretory channel.
Expression of rat kidney anion exchanger 1 in type A intercalated cells in metabolic acidosis and alkalosis
Authors: Huber Saskia , Asan Esther , Jöns Thomas , Kerscher Christiane , Püschel Bernd , Drenckhahn Detlev
Published: December 2017

By enzyme-linked in situ hybridization (ISH), direct evidence is provided that acid-secreting intercalated cells (type A IC) of both the cortical and medullary collecting ducts of the rat kidney selectively express the mRNA of the kidney splice variant of anion exchanger 1 (kAE1) and no detectable levels of the erythrocyte AE1 (eAE1) mRNA. Using single-cell quantification by microphotometry of ISH enzyme reaction, medullary type A IC were found to contain twofold higher kAE1 mRNA levels compared with cortical type A IC. These differences correspond to the higher intensity of immunostaining in medullary versus cortical type A IC. Chronic changes of acid-base status induced by addition of NH4Cl (acidosis) or NaHCO3(alkalosis) to the drinking water resulted in up to 35% changes of kAE1 mRNA levels in both cortical and medullary type A IC. These experiments provide direct evidence at the cellular level of kAE1 expression in type A IC and show moderate capacity of type A IC to respond to changes of acid-base status by modulation of kAE1 mRNA levels.
Hormone-stimulated Ca2+transport in rabbit kidney: multiple sites of inhibition by exogenous ATP
Authors: van Baal Jürgen , Hoenderop Joost G. J. , Groenendijk Maarten , van Os Carel H. , Bindels René J. M. , Willems Peter H. G. M.
Published: December 2017

Exogenous ATP markedly reduced 1-desamino-8-d-arginine vasopressin (dDAVP)-stimulated Ca2+transport and cAMP accumulation in primary cultures of rabbit connecting tubule and cortical collecting duct cells. Similarly, ATP inhibited the stimulatory effect of 8-bromo-cAMP. At first sight, this is in agreement with the “classic” concept that dDAVP exerts its stimulatory effect via cAMP. However, dDAVP-stimulated Ca2+transport was markedly reduced by the protein kinase C (PKC) inhibitor chelerythrine, reported previously to inhibit the cAMP-independent pathway responsible for parathyroid hormone-, [Arg8]vasopressin-, PGE2-, and adenosine-stimulated Ca2+transport. Chelerythrine also inhibited the increase in Ca2+transport evoked by the cAMP-independent A1receptor agonist N6-cyclopentyladenosine (CPA). Downregulation of phorbol ester-sensitive PKC isoforms by chronic phorbol ester treatment has been shown before to be without effect on hormone-stimulated Ca2+transport, indicating that the chelerythrine-inhibitable pathway consists of a phorbol ester-insensitive PKC isoform. Here, this maneuver did not affect ATP inhibition of dDAVP-stimulated Ca2+transport and cAMP formation, while abolishing ATP inhibition of CPA-stimulated Ca2+transport. These findings show that ATP acts via 1) a phorbol ester-sensitive PKC isoform to inhibit hormonal stimulation of Ca2+transport at the level of the chelerythrine-inhibitable pathway involving a phorbol ester-insensitive PKC isoform and 2) a phorbol ester-insensitive mechanism to inhibit V2receptor-mediated concomitant activation of this pathway and adenylyl cyclase.
Role of membrane-type matrix metalloproteinase 1 (MT-1-MMP), MMP-2, and its inhibitor in nephrogenesis
Authors: Kanwar Yashpal S. , Ota Kosuke , Yang Qiwei , Wada Jun , Kashihara Naoki , Tian Yufeng , Wallner Elisabeth I.
Published: December 2017

Extracellular matrix (ECM) proteins, their integrin receptors, and matrix metalloproteinases (MMPs), the ECM-degrading enzymes, are believed to be involved in various biological processes, including embryogenesis. In the present study, we investigated the role of membrane type MMP, MT-1-MMP, an activator pro-MMP-2, in metanephric development. Also, its relationship with MMP-2 and its inhibitor, TIMP-2, was studied. Since mRNAs of MT-1-MMP and MMP-2 are respectively expressed in the ureteric bud epithelia and mesenchyme, they are ideally suited for juxtacrine/paracrine interactions during renal development. Northern blot analyses revealed a single ∼4.5-kb mRNA transcript of MT-1-MMP, and its expression was developmentally regulated. Inclusion of MT-1-MMP antisense oligodeoxynucleotide (ODN) in the culture media induced dysmorphogenetic changes in the embryonic metanephros. MMP-2 antisense ODN also induced similar changes, but they were relatively less; on the other hand TIMP-2 antisense ODN induced a mild increase in the size of explants. Concomitant exposure of MT-1-MMP and MMP-2 antisense ODNs induced profound alterations in the metanephroi. Treatment of TIMP-2 antisense ODN to metanephroi exposed to MT-1-MMP/MMP-2 antisense notably restored the morphology of the explants. Specificity of the MT-1-MMP antisense ODN was reflected in the selective decrease in its mRNA and protein expression. The MT-1-MMP antisense ODN also resulted in a failure in the activation of pro-MMP-2 to MMP-2. These findings suggest that the trimacromolecular complex of MT-1-MMP:MMP-2:TIMP-2 modulates the organogenesis of the metanephros, conceivably by mediating paracrine/juxtacrine epithelial:mesenchymal interactions.
Cellular and subcellular immunolocalization of ClC-5 channel in mouse kidney: colocalization with H+-ATPase
Authors: Sakamoto Hisato , Sado Yoshikazu , Naito Ichiro , Kwon Tae-Hwan , Inoue Shinichi , Endo Kenichi , Kawasaki Masanobu , Uchida Shinichi , Nielsen Søren , Sasaki Sei , Marumo Fumiaki
Published: December 2017

To determine the immunolocalization of ClC-5 in the mouse kidney, we developed a ClC-5-specific rat monoclonal antibody. Immunoblotting demonstrated an 85-kDa band of ClC-5 in the kidney and ClC-5 transfected cells. Immunocytochemistry revealed significant labeling of ClC-5 in brush-border membrane and subapical intracellular vesicles of the proximal tubule. In addition, apical and cytoplasmic staining was observed in the type A intercalated cells in the cortical collecting duct. In contrast, the staining was minimal in the outer and inner medullary collecting ducts and the thick ascending limb. Western blotting of vesicles immunoisolated by the ClC-5 antibody showed the presence of H+-ATPase, strongly indicating that these two proteins were present in the same membranes. Double labeling with antibodies against ClC-5 and H+-ATPase and analysis by confocal images showed that ClC-5 and H+-ATPase colocalized in these ClC-5-positive cells. These findings suggest that ClC-5 might be involved in the endocytosis and/or the H+secretion in the proximal tubule cells and the cortical collecting duct type A intercalated cells in mouse kidney.
NBC3 expression in rabbit collecting duct: colocalization with vacuolar H+-ATPase
Authors: Pushkin Alexander , Yip Kay-Pong , Clark Imran , Abuladze Natalia , Kwon Tae-Hwan , Tsuruoka Shuichi , Schwartz George J. , Nielsen Søren , Kurtz Ira
Published: December 2017

We have recently cloned and characterized a unique sodium bicarbonate cotransporter, NBC3, which unlike other members of the NBC family, is ethylisopropylamiloride (EIPA) inhibitable, DIDS insensitive, and electroneutral (A. Pushkin, N. Abuladze, I. Lee, D. Newman, J. Hwang, and I. Kurtz. J. Biol. Chem.274: 16569–16575, 1999). In the present study, a specific polyclonal antipeptide COOH-terminal antibody, NBC3-C1, was generated and used to determine the pattern of NBC3 protein expression in rabbit kidney. A major band of ∼200 kDa was detected on immunoblots of rabbit kidney. Immunocytochemistry of rabbit kidney frozen sections revealed specific staining of the apical membrane of intercalated cells in both the cortical and outer medullary collecting ducts. The pattern of NBC3 protein expression in the collecting duct was nearly identical to the same sections stained with an antibody against the vacuolar H+-ATPase 31-kDa subunit. In addition, the NBC3-C1 antibody coimmunoprecipitated the vacuolar H+-ATPase 31-kDa subunit. Functional studies in outer medullary collecting ducts (inner stripe) showed that type A intercalated cells have an apical Na+-dependent base transporter that is EIPA inhibitable and DIDS insensitive. The data suggest that NBC3 participates in H+/base transport in the collecting duct. The close association of NBC3 and the vacuolar H+-ATPase in type A intercalated cells suggests a potential structural/functional interaction between the two transporters.
Internalization of proximal tubular type II Na-Pi cotransporter by PTH: immunogold electron microscopy
Authors: Traebert M. , Roth J. , Biber J. , Murer H. , Kaissling B.
Published: December 2017

Physiological/pathophysiological alterations in proximal tubular Pireabsorption are associated with an altered brush-border membrane (BBM) expression of type II Na-Pi cotransporter molecules. Reduction is achieved by an internalization and lysosomal degradation and an increase in Pi reabsorption by new synthesis and BBM insertion of type II Na-Pi cotransporters. In the present study, we investigated by immunohistochemistry and immunogold electron microscopy the routing of internalized rat type II Na-Picotransporters (NaPi-2). In kidney of rats on a chronic low-Pi diet, NaPi-2 is mainly localized in the BBM, in cisterns of the Golgi apparatus and sparsely also in large endocytotic vacuoles and lysosomes. Fifteen minutes after the injection of the 1–34 analog of parathyroid hormone (PTH), the amount of NaPi-2 was decreased in the BBM and increased in endocytotic vesicles. NaPi-2 molecules colocalized with horseradish peroxidase injected prior to the injection of PTH. Vesicles labeled for NaPi-2 were occasionally also labeled for clathrin or the adaptor protein AP2. We conclude that NaPi-2 molecules enter the subapical compartment from where NaPi-2-containing vesicles are segregated off and directed to the lysosomes. A clathrin-mediated pathway may contribute to the PTH-induced internalization of NaPi-2.
Cellular localization of P2Y2 purinoceptor in rat renal inner medulla and lung
Authors: Kishore Bellamkonda K. , Ginns Seth M. , Krane Carissa M. , Nielsen Søren , Knepper Mark A.
Published: December 2017

Physiological and pharmacological studies have demonstrated that extracellular ATP, acting through P2Y2 purinoceptor, modulates water permeability of renal medullary collecting duct cells and the secretion of ions, mucin, and surfactant phospholipids by respiratory epithelia. Here we provide direct molecular evidence for the expression of P2Y2 purinoceptor in these cells. RT-PCR confirmed P2Y2 purinoceptor mRNA expression in rat lung and kidney and demonstrated expression in renal collecting ducts. Northern analysis showed that both lung and kidney express one 3.6-kb P2Y2 purinoceptor mRNA transcript. Immunoblots using peptide-derived polyclonal antibody to P2Y2 purinoceptor showed that inner medullary collecting ducts (IMCD) express two distinct and specific products (47 and 105 kDa) and account for the majority of the receptor expression in inner medulla, whereas the 105-kDa form is predominant in lung. Immunoperoxidase labeling on cryosections showed localization of receptor protein in the apical and basolateral domains of IMCD principal cells and in the secretory cells (Clara cells and goblet cells) of the terminal respiratory bronchioles.
Effects of chloride channel inhibitors on H2O2-induced renal epithelial cell injury
Authors: Meng Xianmin , Reeves W. Brian
Published: December 2017

Oxidative stress contributes to renal epithelial cell injury in certain settings. Chloride influx has also been proposed as an important component of acute renal epithelial cell injury. The present studies examined the role of Cl−in H2O2-induced injury to LLC-PK1renal epithelial cells. Exposure of LLC-PK1cells to 1 mM H2O2resulted in the following: depletion of intracellular ATP content; DNA damage; lipid peroxidation; and a loss of membrane integrity to both small molecules, e.g., trypan blue, and macromolecules, e.g., lactate dehydrogenase (LDH), and cell death. Substitution of Cl−by isethionate or the inclusion of certain Cl−channel blockers, e.g., diphenylamine-2-carboxylate (DPC), 5-nitro-2-(3-phenylpropylamino)· benzoate (NPPB), and niflumic acid, prevented the H2O2-induced loss of membrane integrity to LDH. In addition, the H2O2-induced loss of membrane integrity was prevented by raising the osmolality of the extracellular solutions, by depletion of cell ATP, and by inhibitors of volume-sensitive Cl−channels. However, these maneuvers did not prevent the H2O2-induced permeability to small molecules or H2O2-induced ATP depletion, DNA damage, lipid peroxidation, or cell death. These results support the view that volume-sensitive Cl−channels play a role in the progressive loss of cell membrane integrity during injury.
Targeting of membrane transporters in renal epithelia: when cell biology meets physiology
Authors: Brown Dennis
Published: December 2017

Epithelial cells in the kidney have highly specialized transport mechanisms that differ among the many tubule segments, and among the different cell types that are present in some regions. The purpose of this brief review is to examine some of the major intracellular mechanisms by which the membrane proteins that participate in these differentiated cellular functions are addressed, sorted, and delivered to specific membrane domains of epithelial cells. Unraveling these processes is important not only for our understanding of normal cellular function but is also critical for the interpretation of pathophysiological dysfunction in the context of newly generated molecular and cellular information concerning hereditary and acquired transporter abnormalities. Among the topics covered are sorting signals on proteins, role of the cytoskeleton, vesicle coat proteins, the fusion machinery, and exo- and endocytosis of recycling proteins. Examples of these events in renal epithelial cells are highlighted throughout this review and are related to the physiology of the kidney.
Cell cycle delay and apoptosis are induced by high salt and urea in renal medullary cells
Authors: Michea L. , Ferguson D. R. , Peters E. M. , Andrews P. M. , Kirby M. R. , Burg M. B.
Published: December 2017

We investigated the effects of hyperosmolality on survival and proliferation of subconfluent cultures of mIMCD3 mouse renal collecting duct cells. High NaCl and/or urea (but not glycerol) reduces the number of viable cells, as measured with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT). Raising osmolality from a normal level (300 mosmol/kg) to 550–1,000 mosmol/kg by adding NaCl and/or urea greatly increases the proportion of cells in the G2M phase of the cell cycle within 8 h, as measured by flow cytometry. Up to 600 mosmol/kg the effect is only transient, and by 12 h at 550 mosmol/kg the effect reverses and most cells are in G1. Flow cytometry with 5-bromodeoxyuridine (BrdU) pulse-chase demonstrates that movement through the S phase of the cell cycle slows, depending on the concentrations of NaCl and/or urea, and that the duration of G2M increases greatly (from 2.5 h at 300 mosmol/kg to more than 16 h at the higher osmolalities). Addition of NaCl and/or urea to total osmolality of 550 mosmol/kg or more also induces apoptosis, as demonstrated by characteristic electron microscopic morphological changes, appearance of a subdiploid peak in flow cytometry, and caspase-3 activation. The number of cells with subdiploid DNA and activated caspase-3 peaks at 8–12 h. Caspase-3 activation occurs in all phases of the cell cycle, but to a disproportionate degree in G0/G1and S phases. We conclude that elevated NaCl and/or urea reduces the number of proliferating mIMCD3 cells by slowing the transit through the S phase, by cell cycle delay in the G2M and G1, and by inducing apoptotic cell death.