bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of nitric oxide in the regulation of nephron transport
Authors: Ortiz Pablo A. , Garvin Jeffrey L.
Published: March 2015

Nitric oxide (NO) plays an important role in various physiological processes in the kidney. In vivo experiments first suggested that the natriuretic and diuretic effects caused by NO may be due to decreased NaCl and fluid absorption by the nephron. In the last 10 years, several reports have directly demonstrated a role for NO in modulating transport in different tubule segments. The effects of NO on proximal tubule transport are still controversial. Both stimulation and inhibition of net fluid and bicarbonate have been reported in this segment, whereas only inhibitory effects of NO have been found in Na/H exchanger and Na/K-ATPase activity. The effects of NO in the thick ascending limb are more homogeneous than in the proximal tubule. In this segment, NO decreases net Cl and bicarbonate absorption. A direct inhibitory effect of NO on the Na-K-2Cl cotransporter and the Na/H exchanger has been reported, while NO was found to stimulate apical K channels in this segment. In the collecting duct, NO inhibits Na absorption and vasopressin-stimulated osmotic water permeability. An inhibitory effect of NO on H-ATPase has also been reported in intercalated cells of the collecting duct. Overall, the reported effects of NO in the different nephron segments mostly agree with the natriuretic and diuretic effects observed in vivo. However, the net effect of NO on transport is still controversial in some segments, and in cases like the distal tubule, it has not been studied.
Existence of a regulatory loop between MCP-1 and TGF-β in glomerular immune injury
Authors: Wolf Gunter , Jocks Thomas , Zahner Gunther , Panzer Ulf , Stahl Rolf A. K.
Published: March 2015

Glomerular upregulation of monocyte chemotactic protein-1 (MCP-1), followed by an influx of monocytes resulting eventually in extracellular matrix deposition is a common sequel of many types of glomerulonephritis. However, it is not entirely clear how early expression of MCP-1 is linked to the later development of glomerulosclerosis. Because transforming growth factor-β (TGF-β) is a key regulator of extracellular matrix proteins, we hypothesized that there might be a regulatory loop between early glomerular MCP-1 induction and subsequent TGF-β expression. To avoid interference with other cytokines that may be released from infiltrating monocytes, isolated rat kidneys were perfused with a polyclonal anti-thymocyte-1 antiserum (ATS) and rat serum (RS) as a complement source to induce glomerular injury. Renal TGF-β protein and mRNA expressions were strongly stimulated after perfusion with ATS-RS. This effect was attenuated by coperfusion with a neutralizing anti-MCP-1 but was partly mimicked by perfusion with recombinant MCP-1 protein. On the other hand, renal MCP-1 expression and production were stimulated by administration of ATS-RS. Additional perfusion with an anti-TGF-β antibody further aggravated this increase, whereas application of recombinant TGF-β protein reduced MCP-1 formation. Our data demonstrate an intrinsic regulatory loop in which increased MCP-1 levels stimulate TGF-β formation in resident glomerular cells in the absence of infiltrating immune competent cells.
Renal expression of novel Na+/H+exchanger isoform NHE8
Authors: Goyal Sunita , Vanden Heuvel Gregory , Aronson Peter S.
Published: March 2015

Although Na+/H+exchanger isoform 3 (NHE3) mediates most Na+/H+exchange in the proximal tubule, studies of NHE3/NHE2 null mice suggest residual Na+-dependent proton secretion (Choi JY, Shah M, Lee MG, Schultheis PJ, Shull GE, Muallem S, and Baum M. J Clin Invest 105: 1141–1146, 2000). To characterize additional NHE isoforms that might be expressed in the kidney, we identified the partial sequence of a novel NHE. PCR was used to define the 5′- and 3′-ends, and a cDNA encoding the complete open reading frame was amplified from mouse kidney. The predicted protein of 576 amino acids, which we have named NHE8, has 30–35% amino acid identity to known mammalian isoforms (NHE1–7) but has >50% identity to Drosophila melanogaster “NHE1,” suggesting it is the mammalian ortholog of this ancient invertebrate isoform. Northern blot of mouse tissues revealed ubiquitous expression. Western blot using anti-NHE8 antibodies demonstrated protein expression in apical membranes purified from rat renal cortex by divalent cation precipitation. In situ hybridization revealed that NHE8 message was present in both cortex and medulla. In the cortex, NHE8 was present in the majority of cortical tubules, consistent with proximal tubule (S1 and S2) localization. In the medulla, NHE8 message was most highly expressed in the proximal tubules (S3) of the outer stripe of the outer medulla. Thus NHE8 is expressed in the proximal tubule, where it may contribute to apical membrane ion transport.
Endogenous vasopressin regulates Na-K-ATPase and Na+-K+-Cl−cotransporterrbsc-1in rat outer medulla
Authors: Bertuccio Claudia A. , Ibarra Fernando R. , Toledo Jorge E. , Arrizurieta Elvira E. , Martin Rodolfo S.
Published: March 2015

Previous reports have shown a stimulatory effect of vasopressin (VP) on Na-K-ATPase and rBSC-1 expression and activity. Whether these VP-dependent mechanisms are operating in vivo in physiological conditions as well as in chronic renal failure (CRF) has been less well studied. We measured ATPase expression and activity and rBSC-1 expression in the outer medulla of controls and moderate CRF rats both before and under in vivo inhibition of VP by OPC-31260, a selective V2-receptor antagonist. OPC-31260 decreased Na-K-ATPase activity from 11.2 ± 1.5 to 3.7 ± 0.8 in controls ( P < 0.05) and from 19.0 ± 0.8 to 2.9 ± 0.5 μmol Pi· mg protein−1· h−1in moderate CRF rats ( P < 0.05). CRF was associated with a significant increase in Na-K-ATPase activity ( P < 0.05). Similarly, CRF was also associated with a significant increase in Na-K-ATPase expression to 164.4 ± 21.5% compared with controls ( P < 0.05), and OPC-31260 decreased Na-K-ATPase expression in both controls and CRF rats to 57.6 ± 9.5 and 105.3 ± 10.9%, respectively ( P < 0.05). On the other hand, OPC-31260 decreased rBSC-I expression in both controls and CRF rats to 60.8 ± 6.5 and 30.0 ± 6.9%, respectively ( P < 0.05), and was not influenced by CRF (95.7 ± 5.2%). We conclude that 1) endogenous VP modulated Na-K-ATPase and rBSC-1 in both controls and CRF; and 2) CRF was associated with increased activity and expression of the Na-K-ATPase in the outer medulla, in contrast to the unaltered expression of the rBSC-1. The data suggest that endogenous VP could participate in the regulation of electrolyte transport at the level of the outer medulla.
Disruption of bladder epithelium barrier function after spinal cord injury
Authors: Apodaca Gerard , Kiss Susanna , Ruiz Wily , Meyers Susan , Zeidel Mark , Birder Lori
Published: March 2015

Neural-epithelial interactions are hypothesized to play an important role in bladder function. We determined whether spinal cord injury (SCI) altered several indicators of urinary bladder epithelium barrier function, including continuity of the surface umbrella cell layer, transepithelial resistance (TER), and urea and water permeability. Within 2 h of SCI, significant changes in uroepithelium were noted, including disruption of the surface umbrella cells and an ∼50% decrease in TER. By 24 h, TER reached a minimum and was accompanied by significant increases in water and urea permeability. Regeneration of the surface uroepithelium was accomplished by 14 days after SCI and was accompanied by a return to normal TER and urea and water permeabilities. This early disruption of the uroepithelial permeability and accompanying changes in uroepithelial morphology were prevented by pretreatment with hexamethonium (a blocker of ganglion transmission), indicating involvement of sympathetic or parasympathetic input to the urinary bladder. In addition, prior treatment with capsaicin worsened the effect of SCI on uroepithelial permeability, suggesting that capsaicin-sensitive afferents may play a protective role in the process. These results demonstrate that SCI results in a significant disruption of the urinary bladder uroepithelium and that these changes may be mediated in part by an interaction with bladder nerves.
Decreased renal heme oxygenase-1 expression contributes to decreased renal function during cirrhosis
Authors: Miyazono Motoaki , Garat Chrystelle , Morris Kenneth G. , Carter Ethan P.
Published: March 2015

Heme oxygenase (HO) is the rate-limiting enzyme in the degradation of heme, catalyzing the oxidative cleavage of heme molecules to biliverdin, carbon monoxide, and iron. The present study was designed to investigate the role of HO-1 in the pathogenesis of renal dysfunction during cirrhosis. Biliary cirrhosis was induced in rats by common bile duct ligation (CBDL). Animals were studied 2 and 5 wk after surgery. In kidney from CBDL rats, HO-1 protein expression increased slightly at 2 wk but was abolished at 5 wk. In addition, we confirmed histologically that HO-1 expression was suppressed in renal tubules and interlobular arterioles in 5-wk-old CBDL rats. Conversely, HO-1 expression in liver was strongly increased. Consistent with the development of cirrhosis and renal dysfunction mean arterial pressure (MAP), glomerular filtration rate (GFR), and renal blood flow (RBF) were decreased in CBDL rats compared with sham-operated controls. In sham rats, treatment with the selective HO inhibitor zinc protoporphyrin markedly decreased GFR and RBF to values similar to those measured in CBDL rats without decreasing MAP. In conclusion, decreased renal HO-1 expression contributes to deteriorated renal function and hemodynamics during cirrhosis. This finding provides a novel mechanism for the pathophysiology of renal dysfunction during cirrhosis.
Molecular cloning of rabbit organic cation transporter rbOCT2 and functional comparisons with rbOCT1
Authors: Zhang Xiaohong , Evans Kristen K. , Wright Stephen H.
Published: March 2015

Multiple organic cation transporters (OCTs) are present in rabbit kidney and may play different functional roles. We cloned rabbit OCT2 (rbOCT2) and compared its function with that of rabbit OCT1 (rbOCT1). In transiently transfected COS-7 cells, rbOCT1 and rbOCT2 mediated uptake of [3H]tetraethylammonium (TEA) with Ktvalues of 188 and 125 μM, respectively. n-Tetraalkylammonium compounds showed similar affinities for the two homologs, with IC50values for inhibition of OCT1- and OCT2-mediated [3H]TEA transport, respectively, of 4,538 and 1,395 μM for tetramethylammonium, 88.5 and 3.9 μM for tetrapropylammonium, 13.9 and 5.3 μM for tetrabutylammonium, and 8.8 and 7.6 μM for tetrapentylammonium. However, the transporters had very different affinities for cimetidine (CIM): IC50of 916 and 5.7 μM for rbOCT1 and rbOCT2, respectively. CIM inhibition of TEA uptake into single S2 segments of rabbit proximal tubule was used to estimate the contributions of OCT1 and OCT2 to basolateral organic cation uptake. The median IC50for CIM inhibition of TEA uptake was 12.3 μM, suggesting that OCT2 is the major contributor to basolateral organic cation transport in the S2 segment of proximal tubule in rabbit kidney.
Renal expression of sodium transporters and aquaporin-2 in hypothyroid rats
Authors: Schmitt Roland , Klussmann Enno , Kahl Thomas , Ellison David H. , Bachmann Sebastian
Published: March 2015

Hypothyroidism is associated with significant abnormalities in the renal handling of salt and water. To address the involvement of tubular transport proteins in these abnormalities, rats were rendered pharmacologically hypothyroid and the abundance of major tubular transport proteins was assessed by immunoblot and immunohistochemistry. Hypothyroidism resulted in a marked reduction in kidney size and creatinine clearance along with decreased or unchanged total kidney abundance of the transport proteins. Whereas the proximal tubular type 3 Na/H exchanger (NHE3) and type 2 Na-phosphate cotransporter (NaPi2) stood out by their disproportionately reduced abundance, the bumetanide-sensitive type 2 Na-K-2Cl cotransporter (NKCC2) and aquaporin-2 (AQP2) were unaltered in their total kidney abundance despite a markedly lower kidney mass. The latter proteins in fact showed enhanced immunostaining. Decreased NHE3 and NaPi2 expression was most likely due to a combination of triiodo-l-thyronine (T3) deficiency along with a reduced glomerular filtration rate. The increased abundance of NKCC2 and AQP2 may have been caused by an increased action of vasopressin since urinary excretion of this hormone was elevated. On the other hand, the thiazide-sensitive Na-Cl cotransporter; the α-, β-, and γ-subunits of the amiloride-sensitive epithelial Na channel; and the α1-subunit of Na-K-ATPase showed a moderate decrease in total kidney abundance that was largely proportional to the smaller kidney mass. Although the observed expression of transporters was associated with a balanced renal sodium handling, altered transporter abundance may become functionally relevant if the hypothyroid kidney is challenged by an additional destabilization of the milieu interieur that has previously been shown to result in an inadequate natriuresis and clinical symptoms.
The ins and outs of aquaporin-2 trafficking
Authors: Brown Dennis
Published: March 2015

This review outlines recent advances related to the molecular mechanisms and pathways of aquaporin-2 (AQP2) water channel trafficking. AQP2 is a fascinating protein, whose sorting signals can be interpreted by different cell types to achieve apical or basolateral membrane insertion, in both regulated and constitutive trafficking pathways. In addition to the well-known cAMP-mediated, stimulatory effect of vasopressin on AQP2 membrane insertion, other signaling and trafficking events can also lead to AQP2 membrane accumulation via cAMP-independent mechanisms. These include 1) elevation of cGMP, mediated by sodium nitroprusside (a nitric oxide donor), atrial natriuretic factor, andl-arginine (via nitric oxide synthase); 2) disruption of the actin cytoskeleton; and 3) inhibition of the clathrin-mediated endocytotic arm of the AQP2 recycling pathway by dominant-negative dynamin expression and by membrane cholesterol depletion. Recent data also indicate that AQP2 recycles constitutively in epithelial cells, it can be inserted into different membrane domains in different cell types both in vitro and in vivo, and these pathways can be modulated by factors including hypertonicity. The roles of accessory proteins, including small GTPases and soluble N-ethylmaleimide-sensitive factor attachment protein receptor proteins in AQP2 membrane insertion, are also being uncovered. Understanding cAMP-independent mechanisms for membrane insertion of AQP2 is especially relevant to the therapeutic bypassing of the mutated, dysfunctional vasopressin receptor in patients with X-linked nephrogenic diabetes insipidus.
Oxidative stress in the pathogenesis of experimental mesangial proliferative glomerulonephritis
Authors: Budisavljevic Milos N. , Hodge LeAnn , Barber Kelli , Fulmer John R. , Durazo-Arvizu Ramon A. , Self Sally E. , Kuhlmann Martin , Raymond John R. , Greene Eddie L.
Published: March 2015

Reactive oxygen species (ROS) are increasingly believed to be important intracellular signaling molecules in mitogenic pathways involved in the pathogenesis of glomerulonephritis (GN). We explored the effects of the antioxidants α-lipoic acid and N-acetyl-l-cysteine on ERK activation in cultured mesangial cells and the role of ERK activation in the severity of glomerular injury in a rat model of anti-Thy 1 GN. In cultured mesangial cells, growth factors stimulated ERK phosphorylation by 150–450%. Antioxidants reduced this increase by 50–60%. Induction of anti-Thy 1 nephritis in rats led to a 210% increase in glomerular ERK phosphorylation. This increase in phosphorylated ERK was reduced by 50% in animals treated with α-lipoic acid. Treatment with α-lipoic acid resulted in significant improvement of glomerular injury. Cellular proliferation was reduced by 100%, and the number of proliferating cell nuclear antigen-positive cells was reduced by 64%. The increased expression of glomerular transforming growth factor-β1protein and mRNA in rats with anti-Thy 1 nephritis was significantly attenuated and mesangial cell transformation into myofibroblasts was completely prevented by treatment with α-lipoic acid. The effects of α-lipoic acid were at least partially due to inhibition of oxidative stress. In rats with anti-Thy 1 nephritis, ROS production was increased 400–500%, and this increase was inhibited by 55% by treatment with α-lipoic acid. We suggest that ROS may mediate glomerular injury by inducing ERK phosphorylation. α-Lipoic acid should be considered a potential therapeutic agent in certain types of human GN.
Hydrostatic pressure-regulated ion transport in bladder uroepithelium
Authors: Wang Edward C. Y. , Lee Jey-Myung , Johnson John P. , Kleyman Thomas R. , Bridges Robert , Apodaca Gerard
Published: March 2015

The effect of hydrostatic pressure on ion transport in the bladder uroepithelium was investigated. Isolated rabbit uroepithelium was mounted in modified Ussing chambers and mechanically stimulated by applying hydrostatic pressure across the mucosa. Increased hydrostatic pressure led to increased mucosal-to-serosal Na+absorption across the uroepithelium via the amiloride-sensitive epithelial Na+channel. In addition to this previously characterized pathway for Na+absorption, hydrostatic pressure also induced the secretion of Cl–and K+into the mucosal bathing solution under short-circuit conditions, which was confirmed by a net serosal-to-mucosal flux of36Cl–and86Rb+. K+secretion was likely via a stretch-activated nonselective cation channel sensitive to 100 μM amiloride, 10 mM tetraethylammonium, 3 mM Ba2+, and 1 mM Gd3+. Hydrostatic pressure-induced ion transport in the uroepithelium may play important roles in electrolyte homeostasis, volume regulation, and mechanosensory transduction.
Reduced expression of Na-K-2Cl cotransporter in medullary TAL in vitamin D-induced hypercalcemia in rats
Authors: Wang Weidong , Kwon Tae-Hwan , Li Chunling , Frøkiær Jørgen , Knepper Mark A. , Nielsen Søren
Published: March 2015

Chronic hypercalcemia (HC) is accompanied by urinary concentration defects, and functional studies indicate defects in the thick ascending limb (TAL). We hypothesize that dysregulation of renal sodium transporters may play an important role in this. Vitamin D-induced HC in rats resulted in polyuria, natriuresis, and phosphaturia. Immunoblotting revealed a marked reduction in the abundance of rat type 1 bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1) in inner stripe of the outer medullary (ISOM; 36 ± 5%) and whole kidney (51 ± 11%) in HC. Consistent with this finding, immunocytochemistry and immunoelectron microscopy demonstrated reduced BSC-1 labeling of the apical plasma membrane. Immunoblotting and immunohistochemical labeling of the K channel Kir 1.1 (ROMK) was also reduced in HC. In contrast, there were no reductions in the expression of Na/H exchanger (NHE)3 and Na,K-ATPase in ISOM. The abundance of the proximal tubule type II Na-Picotransporter (NaPi-2) (but not Na,K-ATPase and NHE3) was significantly reduced (25 ± 4%), consistent with a dramatic increase in urinary phosphate excretion. In conclusion, 1) the reduced abundance of BSC-1 and ROMK in TAL is likely to play a major role in the urinary concentration defects associated with HC and 2) the reduced abundance of NaPi-2 is likely to play a role in the increased urinary phosphate excretion.
α2B-Adrenergic receptors activate MAPK and modulate proliferation of primary cultured proximal tubule cells
Authors: Cussac Daniel , Schaak Stéphane , Gales Céline , Flordellis Christodoulos , Denis Colette , Paris Hervé
Published: March 2015

In the rat proximal tubule, the α2B-adrenergic receptor (α2B-AR) enhances Na+reabsorption by increasing the activity of Na+/H+exchanger isoform NHE3. The mechanisms involved are unclear, and inhibition of cAMP production remains controversial. In this study, we reinvestigated α2B-AR signaling pathways using rat proximal tubule cells (PTC) in primary culture and LLC-PK1cells permanently transfected with the RNG gene (rat nonglycosylated α2-AR). Binding experiments indicated that PTC express substantial amounts of α2B-AR (130 fmol/mg protein), and only RNG transcripts were detected. In both cell types, the α2B-AR is coupled to G protein, and its stimulation by dexmedetomidine, but not by UK-14304, provoked a significant inhibition of the accumulation of cAMP induced by forskolin or parathyroid hormone. Exposure to α2-agonists increased arachidonic acid release and caused extracellular signal-regulated kinase (ERK)1/2 phosphorylation, which correlated with enhanced mitogen-activated protein kinse (MAPK) activity and nuclear translocation. MAPK phosphorylation was blunted by pertussis toxin but not by protein kinase C desensitization, and it coincided with transient phosphorylation of Shc. Finally, treatment with UK-14304 accelerated cell growth. Further studies will be necessary to clarify the precise mechanism of MAPK activation, but the present data suggest that α2B-AR may play a positive role during tubular regeneration.
Mechanism of heme oxygenase-1 gene induction by curcumin in human renal proximal tubule cells
Authors: Hill-Kapturczak Nathalie , Thamilselvan Vijayalaksmi , Liu Feiyan , Nick Harry S. , Agarwal Anupam
Published: March 2015

First published August 9, 2001; 10.1152/ajprenal.00140.2001.—Heme oxygenase-1 (HO-1) catalyzes the rate-limiting step in heme degradation, releasing iron, carbon monoxide, and biliverdin. Induction of HO-1 occurs as an adaptive and protective response to several inflammatory stimuli. The transcription factor activator protein-1 (AP-1) has been implicated in the activation of the HO-1 gene. To elucidate the molecular mechanism of HO-1 induction, we examined the effects of diferuloylmethane (curcumin), an inhibitor of the transcription factor AP-1. Surprisingly, curcumin by itself was a very potent inducer of HO-1. Curcumin has anti-inflammatory, antioxidant, and renoprotective effects. To evaluate the mechanism of curcumin-mediated induction of HO-1, confluent human renal proximal tubule cells were exposed to curcumin (1–8 μM). We observed a time- and dose-dependent induction of HO-1 mRNA that was associated with increased HO-1 protein. Coincubation of curcumin with actinomycin D completely blocked the upregulation of HO-1 mRNA. Blockade of nuclear factor-κB (NF-κB) with an IκBα phosphorylation inhibitor attenuated curcumin-mediated induction of HO-1 mRNA and protein. These data demonstrate that curcumin induces HO-1 mRNA and protein in renal proximal tubule cells. HO-1 induction by curcumin is mediated, at least in part, via transcriptional mechanisms and involves the NF-κB pathway.
Dietary salt supplementation selectively downregulates NPR-C receptor expression in kidney independently of ANP
Authors: Sun Ju-Zhong , Chen Shi-Juan , Majid-Hasan Erum , Oparil Suzanne , Chen Yiu-Fai
Published: March 2015

Atrial natriuretic peptide (ANP) has negative modulatory effects on a variety of pathophysiological mechanisms; i.e., it inhibits hypoxia-induced pulmonary vasoconstriction and vascular remodeling and facilitates natriuresis and vasorelaxation in NaCl-supplemented subjects. We have previously demonstrated organ-selective potentiation of ANP in the pulmonary circulation of hypoxia-adapted animals by local downregulation of its clearance receptor (NPR-C; Li H, Oparil S, Meng QC, Elton T, and Chen Y-F. Am J Physiol Lung Cell Mol Physiol 268: L328–L335, 1995). The present study tested the hypothesis that NPR-C expression is attenuated selectively in kidneys of NaCl-supplemented subjects. Adult male wild-type (ANP+/+) and homozygous mutant (ANP−/−) mice were studied after 5 wk of normal or high-salt diets. Mean arterial pressure (MAP) and left (LV) and right ventricular (RV) mass were greater in ANP−/− mice than in ANP+/+ mice fed the normal-salt diet; salt supplementation induced increases in plasma ANP in ANP+/+ mice and in MAP and LV, RV, and renal mass in ANP−/− mice but not in ANP+/+ mice. NPR-C mRNA levels were selectively and significantly reduced (>60%) in kidney, but not in lung, brain, LV, or RV, by dietary salt supplementation in both genotypes. NPR-A mRNA levels did not differ among diet-genotype groups in any organ studied. cGMP content was significantly increased in kidney, but not in lung or brain, by dietary salt supplementation in both genotypes. These findings suggest that selective downregulation of NPR-C in the kidney in response to dietary salt supplementation may contribute to local elevation in ANP levels and may be functionally significant in attenuating the development of salt-sensitive hypertension.
Effect of platelet-derived growth factor isoforms in rat metanephric mesenchymal cells
Authors: Ricono Jill M. , Arar Mazen , Choudhury Goutam Ghosh , Abboud Hanna E.
Published: March 2015

Platelet-derived growth factor (PDGF) B-chain or PDGF β-receptor-deficient mice lack mesangial cells. To explore potential mechanisms for failure of PDGF A-chain to rescue mesangial cell phenotype, we investigated the biological effects and signaling pathways of PDGF AA and PDGF BB in metanephric mesenchymal (MM) cells isolated from rat kidney. PDGF AA caused modest cell migration but had no effect on DNA synthesis, unlike PDGF BB, which potently stimulated migration and DNA synthesis. PDGF AA and PDGF BB significantly increased the activities of phosphatidylinositol 3-kinase (PI 3-K) and mitogen-activated protein kinase (MAPK). PDGF BB was more potent than PDGF AA in activating PI 3-K or MAPK in these cells. Pretreatment of MM cells with the MAPK kinase (MEK) inhibitor PD-098059 abrogated PDGF BB-induced DNA synthesis, whereas the PI 3-K inhibitor wortmannin had a very modest inhibitory effect on DNA synthesis (approximately Δ20%). On the other hand, wortmannin completely blocked PDGF AA- and PDGF BB-induced migration, whereas PD-098059 had a modest inhibitory effect on cell migration. These data demonstrate that activation of MAPK is necessary for the mitogenic effect of PDGF BB, whereas PI 3-K is required for the chemotactic effect of PDGF AA and PDGF BB. Although PDGF AA stimulates PI 3-K and MAPK activity, it is not mitogenic and only modestly chemotactic. Collectively, the data may have implications related to the failure of PDGF AA to rescue mesangial cell phenotype in PDGF B-chain or PDGF-β-receptor deficiency.
Intrarenal AT1receptor and ACE binding in ANG II-induced hypertensive rats
Authors: Harrison-Bernard Lisa M. , Zhuo Jialong , Kobori Hiroyuki , Ohishi Mitsuru , Navar L. Gabriel
Published: March 2015

The intrarenal expression of angiotensin II (ANG II) type 1 (AT1) receptors and angiotensin-converting enzyme (ACE) was determined in ANG II-induced hypertensive rats (80 ng/min; 2 wk). Systolic blood pressure averaged 184 ± 3 and 125 ± 1 mmHg in ANG II-infused compared with Sham rats on day 12. Total kidney AT1receptor protein levels were not altered significantly. AT1receptor binding mapped by quantitative in vitro autoradiography was significantly decreased in glomeruli (172 ± 25 vs. 275 ± 34 disintegrations · min−1· mm−2) and the inner stripe of the outer medulla (121 ± 17 vs. 178 ± 19 disintegrations · min−1· mm−2), but not proximal convoluted tubules (48 ± 9 vs. 58 ± 6 disintegrations · min−1· mm−2) of ANG II-infused compared with Sham rats. Proximal tubule ACE binding was significantly augmented (132 ± 4 vs. 97 ± 3 disintegrations · min−1· mm−2) in ANG II-infused rats. In summary, during ANG II-induced hypertension, glomeruli and inner stripe of the outer medulla have reduced AT1receptor binding. Proximal convoluted tubules exhibit maintained AT1receptor density and increased ACE binding, which together with the elevated ANG II levels suggest that ANG II exerts a sustained influence on tubular reabsorption and consequently contributes to the development and maintenance of ANG II-dependent hypertension.
Metabolic, but not respiratory, acidosis increases bone PGE2levels and calcium release
Authors: Bushinsky David A. , Parker Walter R. , Alexander Kristen M. , Krieger Nancy S.
Published: March 2015

First published July 12, 2001; 10.1152/ajprenal.00355.2001.— A decrease in blood pH may be due to either a reduction in bicarbonate concentration ([HCO[Formula: see text]]; metabolic acidosis) or to an increase in Pco2(respiratory acidosis). In mammals, metabolic, but not respiratory, acidosis increases urine calcium excretion without altering intestinal calcium absorption, indicating that the additional urinary calcium is derived from bone. In cultured bone, chronic metabolic, but not respiratory, acidosis increases net calcium efflux ( JCa), decreases osteoblastic collagen synthesis, and increases osteoclastic bone resorption. Metabolic acidosis increases bone PGE2production, which is correlated with JCa, and inhibition of PGE2production inhibits this acid-induced JCa. Given the marked differences in the osseous response to metabolic and respiratory acidosis, we hypothesized that incubation of neonatal mouse calvariae in medium simulating respiratory acidosis would not increase medium PGE2levels, as observed during metabolic acidosis. To test this hypothesis, we determined medium PGE2levels and JCafrom calvariae incubated at pH ∼7.1 to model either metabolic (Met; [HCO[Formula: see text]] ∼11 mM) or respiratory (Resp; Pco2∼83 Torr) acidosis, or at pH ∼7.5 as a control (Ntl). We found that after 24–48 and 48–51 h in culture, periods when cell-mediated JCapredominates, medium PGE2levels and JCawere increased with Met, but not Resp, compared with Ntl, and there was a direct correlation between medium PGE2levels and JCa. Thus metabolic, but not respiratory, acidosis induces the release of bone PGE2, which mediates JCafrom bone.
M1/70 attenuates blood-borne neutrophil oxidants, activation, and myofiber damage following stretch injury
Authors: Brickson S. , Ji L. L. , Schell K. , Olabisi R. , St. Pierre Schneider B. , Best T. M.
Published: March 2015

The purpose of this study was to determine the role of the CD11b-dependent respiratory burst in neutrophil oxidant generation and activation, interleukin-8 (IL-8) production, and myofiber damage after muscle stretch injury by using the monoclonal antibody M1/70 to block this pathway. Twelve male New Zealand White rabbits were randomly assigned to a treatment group: M1/70 ( n = 6), IgG isotype control ( n = 3), or saline control ( n = 3). After intravenous injection of the assigned agent under gas anesthesia, a standardized single-stretch injury was created in the right tibialis anterior, whereas the left tibialis anterior underwent a sham surgery. Blood-borne neutrophil oxidant generation and CD11b receptor density and plasma IL-8 levels were measured pre- and 24 h postinjury. Damage was assessed histologically at the hematoma site by counting torn myofibers. M1/70 group demonstrated decreased blood-borne neutrophil oxidant generation ( P < 0.05) and CD11b receptor density ( P < 0.05), an increase in plasma IL-8 concentration ( P < 0.01), and less torn myofibers ( P < 0.01) compared with IgG isotype or saline control groups. These data indicate that 1) CD11b-dependent respiratory burst is a major source of oxidants produced by the neutrophil, and that treatment with M1/70 2) attenuates neutrophil activation status, 3) increases plasma IL-8 concentration, and 4) minimizes myofiber damage 24 h postmuscle stretch injury.
Acute molecular responses of skeletal muscle to resistance exercise in able-bodied and spinal cord-injured subjects
Authors: Bickel C. Scott , Slade Jill M. , Haddad Fadia , Adams Gregory R. , Dudley Gary A.
Published: March 2015

Spinal cord injury (SCI) results in muscle atrophy, which contributes to a number of health problems, such as cardiovascular deconditioning, metabolic derangement, and osteoporosis. Electromyostimulation (EMS) holds the promise of ameliorating SCI-related muscle atrophy and, therefore, improving general health. To date, EMS training of long-term SCI subjects has resulted in some muscle hypertrophy but has fallen short of normalizing muscle mass. The aim of this study was to compare the molecular responses of vastus lateralis muscles from able-bodied (AB) and SCI subjects after acute bouts of EMS-induced resistance exercise to determine whether SCI muscles displayed some impairment in response. Analysis included mRNA markers known to be responsive to increased loading in rodent muscles. Muscles of AB and SCI subjects were subjected to EMS-stimulated exercise in two 30-min bouts, separated by a 48-h rest. Needle biopsy samples were obtained 24 h after the second exercise bout. In both the AB and SCI muscles, significant changes were seen in insulin-like growth factor binding proteins 4 and 5, cyclin-dependent kinase inhibitor p21, and myogenin mRNA levels. In AB subjects, the mRNA for mechano-growth factor was also increased. Before exercise, the total RNA concentration of the SCI muscles was less than that of the AB subjects but not different postexercise. The results of this study indicate that acute bouts of resistance exercise stimulate molecular responses in the skeletal muscles of both AB and SCI subjects. The responses seen in the SCI muscles indicate that the systems that regulate these molecular responses are intact, even after extended periods of muscle unloading.
Vasopressin vs. norepinephrine in endotoxic shock: systemic, renal, and splanchnic hemodynamic and oxygen transport effects
Authors: Guzman Jorge A. , Rosado Ariosto E. , Kruse James A.
Published: March 2015

The effects of intravenous norepinephrine (NE, group 1) and vasopressin (AVP, group 2) infusions on systemic, splanchnic, and renal circulations were studied in anesthetized dogs under basal conditions and during endotoxic shock. Under basal conditions, AVP infusion induced a 12 ± 7% drop in left ventricular stroke work, a 45 ± 5% fall in portal venous blood flow, and a 31 ± 13% decrease in intestinal mucosal blood flow ( P < 0.05). AVP also decreased splanchnic oxygen delivery (Do2) and increased splanchnic and renal oxygen extraction significantly during basal conditions. Except for more pronounced brady-cardia among animals in group 2, the systemic and splanchnic changes were comparable between study groups during endotoxic shock. AVP infusion restored renal blood flow and Do2 in endotoxic shock compared with animals resuscitated with NE, which had persistently low renal blood flow and Do2. Our data demonstrate that, in contrast to NE, administration of AVP effectively restores renal blood flow and Do2 with comparable systemic and splanchnic hemodynamic and metabolic effects in endotoxin-induced circulatory shock.
Invited Review: Lung edema clearance: role of Na+-K+-ATPase
Authors: Sznajder J. I. , Factor P. , Ingbar D. H.
Published: March 2015

Acute hypoxemic respiratory failure is a consequence of edema accumulation due to elevation of pulmonary capillary pressures and/or increases in permeability of the alveolocapillary barrier. It has been recognized that lung edema clearance is distinct from edema accumulation and is largely effected by active Na+transport out of the alveoli rather than reversal of the Starling forces, which control liquid flux from the pulmonary circulation into the alveolus. The alveolar epithelial Na+-K+-ATPase has an important role in regulating cell integrity and homeostasis. In the last 15 yr, Na+-K+-ATPase has been localized to the alveolar epithelium and its contribution to lung edema clearance has been appreciated. The importance of the alveolar epithelial Na+-K+-ATPase function is reflected in the changes in the lung's ability to clear edema when the Na+-K+-ATPase is inhibited or increased. An important focus of the ongoing research is the study of the mechanisms of Na+-K+-ATPase regulation in the alveolar epithelium during lung injury and how to accelerate lung edema clearance by modulating Na+-K+-ATPase activity.
Phenotypic adaptations in human muscle fibers 6 and 24 wk after spinal cord injury
Authors: Talmadge R. J. , Castro M. J. , Apple D. F. , Dudley G. A.
Published: March 2015

10.1152/japplphysiol.000247.2001.—The effects of spinal cord injury (SCI) on the profile of sarco(endo) plasmic reticulum calcium-ATPase (SERCA) and myosin heavy chain (MHC) isoforms in individual vastus lateralis (VL) muscle fibers were determined. Biopsies from the VL were obtained from SCI subjects 6 and 24 wk postinjury ( n = 6). Biopsies from nondisabled (ND) subjects were obtained at two time points 18 wk apart ( n = 4). In ND subjects, the proportions of VL fibers containing MHC I, MHC IIa, and MHC IIx were 46 ± 3, 53 ± 3, and 1 ± 1%, respectively. Most MHC I fibers contained SERCA2. Most MHC IIa fibers contained SERCA1. All MHC IIx fibers contained SERCA1 exclusively. SCI resulted in significant increases in fibers with MHC IIx (14 ± 4% at 6 wk and 16 ± 2% at 24 wk). In addition, SCI resulted in high proportions of MHC I and MHC IIa fibers with both SERCA isoforms (29% at 6 wk and 54% at 24 wk for MHC I fibers and 16% at 6 wk and 38% at 24 wk for MHC IIa fibers). Thus high proportions of VL fibers were mismatched for SERCA and MHC isoforms after SCI (19 ± 3% at 6 wk and 36 ± 9% at 24 wk) compared with only ∼5% in ND subjects. These data suggest that, in the early time period following SCI, fast fiber isoforms of both SERCA and MHC are elevated disproportionately, resulting in fibers that are mismatched for SERCA and MHC isoforms. Thus the adaptations in SERCA and MHC isoforms appear to occur independently.
Hormonal, renal, hemodynamic responses to acute neutral endopeptidase inhibition in heart transplant patients
Authors: Piquard François , Richard Ruddy , Charloux Anne , Doutreleau Stephane , Hannedouche Thierry , Brandenberger Gabrielle , Geny Bernard
Published: March 2015

We investigated the hemodynamic, renal, and hormonal responses to neutral endopeptidase (NEP) inhibition during a 6-h, double-blind, randomized, placebo-controlled study in seven chronic, stable heart transplant patients. Baseline characteristics were similar during both experiments, and no significant changes were observed after placebo. NEP inhibition increased circulating endothelin-1 (from 2.01 ± 0.1 to 2.90 ± 0.2 pmol/l; P < 0.01), atrial natriuretic peptide (ANP; from 21.5 ± 2.7 to 29.6 ± 3.7 pmol/l; P < 0.01), and the ANP second messenger cGMP. Noteworthy, systemic blood pressure did not increase. Renal plasma flow and glomerular filtration rate remained unmodified after NEP inhibition. Filtration fraction (33 ± 13%), diuresis (196 ± 62%), and natriuresis (315 ± 105%) increased significantly in relation to ANP and cGMP. A strong inverse relationship was observed between excreted cGMP and sodium reabsorption ( r = −0.71, P < 0.0001). Thus, despite significantly increasing endothelin-1, NEP inhibition did not adversely influence systemic or renal hemodynamics in transplant patients. ANP, possibly through a tubular action, enhances the natriuresis observed after NEP inhibition.
Invited Review: Effect of acute exercise on insulin signaling and action in humans
Authors: Wojtaszewski Jørgen F. P. , Nielsen Jakob N. , Richter Erik A.
Published: March 2015

After a single bout of exercise, insulin action is increased in the muscles that were active during exercise. The increased insulin action has been shown to involve glucose transport, glycogen synthesis, and glycogen synthase (GS) activation as well as amino acid transport. A major mechanism involved in increased insulin stimulation of glucose uptake after exercise seems to be the exercise-associated decrease in muscle glycogen content. Muscle glycogen content also plays a pivotal role for the activity of GS and for the ability of insulin to increase GS activity. Insulin signaling in human skeletal muscle is activated by physiological insulin concentrations, but the increase in insulin action after exercise does not seem to be related to increased insulin signaling [insulin receptor tyrosine kinase activity, insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation (RS1), IRS-1-associated phosphatidylinositol 3-kinase activity, Akt phosphorylation (Ser473), glycogen synthase kinase 3 (GSK3) phosphorylation (Ser21), and GSK3α activity], as measured in muscle lysates. Furthermore, insulin signaling is also largely unaffected by exercise itself. This, however, does not preclude that exercise influences insulin signaling through changes in the spatial arrangement of the signaling compounds or by affecting unidentified signaling intermediates. Finally, 5′-AMP-activated protein kinase has recently entered the stage as a promising player in explaining at least a part of the mechanism by which exercise enhances insulin action.
Upper airway muscle paralysis reduces reflex upper airway motor response to negative transmural pressure in rat
Authors: Ryan Stephen , McNicholas Walter T. , O'Regan Ronan G. , Nolan Philip
Published: March 2015

The reflex upper airway (UA) motor response to UA negative pressure (UANP) is attenuated by neuromuscular blockade. We hypothesized that this is due to a reduction in the sensitivity of laryngeal mechanoreceptors to changes in UA pressure. We examined the effect of neuromuscular blockade on hypoglossal motor responses to UANP and to asphyxia in 15 anesthetized, thoracotomized, artificially ventilated rats. The activity of laryngeal mechanoreceptors is influenced by contractions of laryngeal and tongue muscles, so we studied the effect of selective denervation of these muscle groups on the UA motor response to UANP and to asphyxia, recording from the pharyngeal branch of the glossopharyngeal nerve ( n = 11). We also examined the effect of tongue and laryngeal muscle denervation on superior laryngeal nerve (SLN) afferent activity at different airway transmural pressures ( n = 6). Neuromuscular blockade and denervation of laryngeal and tongue muscles significantly reduced baseline UA motor nerve activity ( P < 0.05), caused a small but significant attenuation of the motor response to asphyxia, and markedly attenuated the response to UANP. Motor denervation of tongue and laryngeal muscles significantly decreased SLN afferent activity and altered the response to UANP. We conclude that skeletal muscle relaxation reduces the reflex UA motor response to UANP, and this may be due to a reduction in the excitability of UA motor systems as well as a decrease of the response of SLN afferents to UANP.
Effects of body position on intracranial and cerebral perfusion pressures in isoflurane-anesthetized horses
Authors: Brosnan Robert J. , Steffey Eugene P. , LeCouteur Richard A. , Imai Ayako , Farver Thomas B. , Kortz Gregg D.
Published: March 2015

Inhalant anesthetics may interfere with normal cerebrovascular autoregulation. It was, therefore, hypothesized that intracranial pressure (ICP) and cerebral perfusion pressure (CPP) in isoflurane-anesthetized horses would be especially sensitive to body and head position because of the potential for large hydrostatic gradients between the brain and heart in this species. Anesthesia was induced and maintained in six clinically healthy, unmedicated geldings with 1.57% isoflurane in O2; mechanical ventilation was used to maintain normocapnia. ICP was measured by using a subarachnoid strain-gauge transducer. Blood gases and carotid arterial, right atrial, and airway pressures were also measured. Five body positions were studied in semirandomized order: dorsal recumbency (DR) with head down (HD), DR with head level (HL), lateral recumbency (LR), sternal recumbency (SR) with HL, and SR with head up (HU). Data were analyzed by using paired t-tests. ICP and CPP values, respectively, are as follows (means ± SD): 36 ± 4 and 55 ± 18 mmHg (DR-HD); 34 ± 6 and 51 ± 32 mmHg (DR-HL); 24 ± 5 and 48 ± 4 mmHg (LR); 19 ± 11 and 87 ± 12 mmHg (SR-HL); and −14 ± 7 and 71 ± 10 mmHg (SR-HU). Significant differences were found among all positions, except for SR-HL vs. LR. Significant increases in CPP were observed only in sternal positions. In conclusion, ICP in isoflurane-anesthetized horses changes inversely with the brain-to-heart hydrostatic gradient. DR may also cause increases in ICP, irrespective of head position.
Effects of various forms of surfactant protein C on tidal volume in ventilated immature newborn rabbits
Authors: Tashiro Katsumi , Ohta Keisuke , Cui Xiaoguang , Nishizuka Kazuo , Yamamoto Ken , Konzaki Tomoharu , Kobayashi Tsutomu , Suzuki Yasuhiro
Published: March 2015

Surfactant protein (SP)-C is characterized by α-helix structure and palmitoyl groups attached to two cysteine residues. We examined the function of palmitoylation and dimerization in promotion of tidal volume in immature newborn rabbits. Reconstituted surfactants were made from a mixture of synthetic phospholipids and porcine SP-B (basic mixture) by adding various forms of SP-Cs: normal SP-C isolated from porcine lungs and monomeric or dimeric forms of SP-C. These latter two were isolated from patients with pulmonary alveolar proteinosis and were less palmitoylated. Animals were ventilated at an inspiratory pressure of 25 cmH2O. Median tidal volumes were <2 ml/kg in nontreated controls, 7.7 ml/kg in animals receiving the basic mixture without SP-C, and >18 ml/kg in animals treated with reconstituted surfactants containing 3% normal or 2% dimeric SP-C ( P < 0.05 vs. basic mixture). The physiological effect of basic mixture was not improved by monomeric SP-C. We conclude that palmitoyl groups are important for the physiological effects of SP-C and that the dimeric form also improves physiological effects.
Alveolar hypercapnia augments pulmonary C-fiber responses to chemical stimulants: role of hydrogen ion
Authors: Gu Qihai , Lee Lu-Yuan
Published: March 2015

To determine whether the excitabilities of pulmonary C fibers to chemical and mechanical stimuli are altered by CO2-induced acidosis, single-unit pulmonary C-fiber activity was recorded in anesthetized, open-chest rats. Transient alveolar hypercapnia (HPC) was induced by administering CO2-enriched gas mixture (15% CO2, balance air) via the respirator inlet for 30 s, which rapidly lowered the arterial blood pH from a baseline of 7.40 ± 0.01 to 7.17 ± 0.02. Alveolar HPC markedly increased the responses of these C-fiber afferents to several chemical stimulants. For example, the C-fiber response to right atrial injection of the same dose of capsaicin (0.25–1.0 μg/kg) was significantly increased from 3.07 ± 0.70 impulses/s at control to 8.48 ± 1.52 impulses/s during HPC ( n = 27; P < 0.05), and this enhanced response returned to control within ∼10 min after termination of HPC. Similarly, alveolar HPC also induced significant increases in the C-fiber responses to right atrial injections of phenylbiguanide (4–8 μg/kg) and adenosine (0.2 mg/kg). In contrast, HPC did not change the response of pulmonary C fibers to lung inflation. Furthermore, the peak response of these C fibers to capsaicin during HPC was greatly attenuated when the HPC-induced acidosis was buffered by infusion of bicarbonate (1.36–1.82 mmol · kg−1 · min−1 for 35 s). In conclusion, alveolar HPC augments the responses of these afferents to various chemical stimulants, and this potentiating effect of CO2 is mediated through the action of hydrogen ions on the C-fiber sensory terminals.