| 1. |
- Patinha, Daniela, et al.
(författare)
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Angiotensin II contributes to glomerular hyperfiltration in diabetic rats independently of adenosine type I receptors
- 2013
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Ingår i: AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY. - : American Physiological Society. - 1931-857X .- 1522-1466 .- 0363-6127. ; 304:5, s. F614-F622
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Tidskriftsartikel (refereegranskat)abstract
- Increased angiotensin II (ANG II) or adenosine can potentiate each other in the regulation of renal hemodynamics and tubular function. Diabetes is characterized by hyperfiltration, yet the roles of ANG II and adenosine receptors for controlling baseline renal blood flow (RBF) or tubular Na+ handling in diabetes is presently unknown. Accordingly, the changes in their functions were investigated in control and 2-wk streptozotocin-diabetic rats after intrarenal infusion of the ANG II AT(1) receptor antagonist candesartan, the adenosine A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), or their combination. Compared with controls, the baseline blood pressure, RBF, and renal vascular resistance (RVR) were similar in diabetics, whereas the glomerular filtration rate (GFR) and filtration fraction (FF) were increased. Candesartan, DPCPX, or the combination increased RBF and decreased RVR similarly in all groups. In controls, the GFR was increased by DPCPX, but in diabetics, it was decreased by candesartan. The FF was decreased by candesartan and DPCPX, independently. DPCPX caused the most pronounced increase in fractional Na+ excretion in both controls and diabetics, whereas candesartan or the combination only affected fractional Li+ excretion in diabetics. These results suggest that RBF, via a unifying mechanism, and tubular function are under strict tonic control of both ANG II and adenosine in both control and diabetic kidneys. Furthermore, increased vascular AT(1) receptor activity is a contribution to diabetes-induced hyperfiltration independent of any effect of adenosine A(1) receptors.
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| 2. |
- Andersson, Maria, 1976, et al.
(författare)
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Mild renal ischemia-reperfusion reduces charge and size selectivity of the glomerular barrier
- 2007
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Ingår i: American Journal of Physiology Renal Physiology. - : American Physiological Society. - 0363-6127 .- 1931-857X .- 1522-1466. ; 292:6
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Tidskriftsartikel (refereegranskat)abstract
- Despite recent discoveries of molecules in podocytes, the mechanisms behind most conditions of proteinuria are still poorly understood. To understand more about this delicate barrier, we studied the functional and morphological effects of mild (15 min) renal ischemia-reperfusion injury (IRI). Renal function was studied in rats in vivo, followed by a more detailed analysis of the glomerular barrier in cooled (8 degrees C) isolated perfused kidneys (cIPK). Renal blood flow was quickly restored, whereas the glomerular filtration rate remained halved 30 min after IRI. Tubular cell activity was intact as judged from the unaffected Cr-EDTA U/P concentration ratio. In vivo, the fractional clearance (theta) for albumin increased 16 times. In rats subjected to cIPK starting 30 min after in vivo IRI, theta(albumin) was 15 times and theta(Ficoll_36angstroms) 1.8 times higher than in control cIPKs. According to the heterogeneous charged fiber model, IRI reduced the fiber charge density to 38% of control (P < 0.01, n = 7). Morphometric analysis with electron microscopy did not reveal any changes in the podocytes or the glomerular basement membrane (GBM) after IRI, suggesting more subtle changes of the GBM and/or the endothelial glycocalyx. We conclude that mild renal IRI induces formation of reactive oxygen species, massive proteinuria, and loss of charged fibers with no apparent change in morphology. These novel findings stress the importance of other components of the barrier, such as proteoglycans produced by the glomerular cells, and provide a tentative explanation for the mechanisms behind proteinuria in glomerulonephritis, for example.
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| 3. |
- Asgeirsson, Daniel, et al.
(författare)
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Increased glomerular permeability to negatively charged Ficoll relative to neutral Ficoll in rats.
- 2006
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Ingår i: American Journal of Physiology: Renal, Fluid and Electrolyte Physiology. - : American Physiological Society. - 0363-6127. ; 291:5, s. 1083-1089
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Tidskriftsartikel (refereegranskat)abstract
- It is established that the glomerular filter sieves macromolecules based on their size, shape, and charge. Anionic proteins are thus retarded compared with their neutral or cationic counterparts. However, recent studies have indicated that charge effects are small, or even "anomalous," for polysaccharides. We therefore investigated the impact of charge on the glomerular permeability to polysaccharides by comparing sieving coefficients ({theta}; primary urine-to-plasma concentration ratio) for negatively charged, carboxymethylated (CM) FITC-Ficoll and FITC-dextran with their neutral counterparts. For these probes, {theta} were determined in anesthetized Wistar rats [269 ± 2.7 g (±SE; n = 36)], whose ureters were cannulated for urine sampling. The glomerular filtration rate was assessed using FITC-inulin. Polysaccharides were constantly infused, and after equilibration, urine was collected and a midpoint plasma sample was taken. Size and concentration determinations of the FITC-labeled polysaccharides were achieved by size-exclusion HPLC (HPSEC). For CM-Ficoll, {theta} was significantly increased (32 times at 55 Å) compared with that of uncharged Ficoll. A small increase in {theta} for CM-dextran compared with neutral dextran was also observed (1.8 times at 55 Å). In conclusion, negatively charged Ficoll relative to neutral Ficoll was found to be markedly hyperpermeable across the glomerular filter. Furthermore, negatively charged Ficoll was observed to be larger on HPSEC compared with its neutral counterpart of the same molecular weight. It is proposed that the introduction of negative charges in the "dendrimeric," cross-linked Ficoll molecule may alter its configuration, so as to make it more extended, and conceivably, more flexible, thereby increasing its glomerular permeability. charge barrier; capillary permeability; macromolecules; fractional clearance; reflection coefficients IT IS GENERALLY ACCEPTED THAT the glomerular filter discriminates among macromolecules based on their size, shape, and net charge (6, 8). With respect to charge, the permeability of anionic dextran sulfate was found to be reduced and that of cationic, diethylaminoethyl (DEAE) dextran to be increased compared with that of neutral dextran (6). However, more recent studies have indicated that sulfated dextran may be processed in the kidney (28) and desulfated during its renal passage (10), and furthermore, that it may bind to plasma proteins (17), and to membrane phospholipids (25), causing an artifactual reduction in the sieving coefficients ({theta}; i.e., the primary urine-to-plasma concentration ratios) of dextran sulfate. In addition, isolated glomerular basement membranes (GBM) have generally failed to show charge selectivity when probed with neutral and negatively charged Ficoll (7) or native (anionic) or cationized albumin (4). In line with these findings, Schaeffer et al. (26) were unable to find (in rats in vivo) any difference between glomerular {theta} to carboxymethylated (non-sulfated) dextran or to hydroxymethyl starch (HES), both negatively charged, and their neutral counterparts. Furthermore, the HES molecules showed lower {theta} for any given Stokes-Einstein (SE) radius (cf. Ficoll) than did dextran. It was concluded that the glomerular filtration barrier restricts the transport of polysaccharide macromolecules as a function of size and configuration whereas the presence or absence of negative charge does not play any role. Further supporting these results, Guimarães et al. (18) did not find a decrease in glomerular permeability to negatively charged, carboxymethylated (CM) Ficoll compared with uncharged Ficoll, confirming a previous observation by Greive et al. (16). Instead, they found a markedly increased glomerular permeability to CM-Ficoll. In contrast to the apparent inability of the glomerular filter to discriminate between polysaccharides of different charge, there is ample evidence that, indeed, the glomerular filter selects globular proteins based on their charge. Thus anionic proteins are retarded compared with neutral and cationic proteins, as extensively reviewed by Comper and Glasgow (9) and Venturoli and Rippe (29). The reason the glomerular capillary wall exhibits low discrimination ability with respect to differently charged polysaccharides, while being able to separate proteins of different molecular charge, is obscure. However, one clue to this enigma could be the fact that carbohydrates exhibit an extended molecular configuration, with a larger SE radius, compared with that for globular proteins, for any given molecular mass (19, 29). Such an extended configuration, conceivably, generates a more flexible (compressible) structure and hence increases the molecule's permeability through the glomerular filtration barrier (29). Charge modification of a polysaccharide may lead to a further increase in molecular extension, favoring an increased flexibility and, thereby, an increased solute permeability. Could the process of charge modification of the highly cross linked and "ellipsoid" molecules of Ficoll (19) lead to conformational alterations, with increased molecular extension, increasing their permeability compared with their uncharged counterparts? If so, would the linear, "random coil," structure of dextran make it less affected by conformational changes, and thereby less hyperpermeable, when negatively charged? The present study was performed to test this hypothesis by comparing glomerular sieving coefficients to negatively charged, CM-Ficoll and -dextran vs. their uncharged molecular equivalents.
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| 4. |
- Axelsson, Josefin, et al.
(författare)
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Acute hyperglycemia induces rapid, reversible increases of glomerular permeability in non-diabetic rats.
- 2010
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Ingår i: American Journal of Physiology-Renal Physiology. - : American Physiological Society. - 1522-1466 .- 1931-857X. ; 298:6, s. 1306-1312
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Tidskriftsartikel (refereegranskat)abstract
- This study was performed to investigate the impact of acute hyperglycemia (HG) on the permeability of the normal glomerular filtration barrier in vivo. In anaesthetized Wistar rats (250-280g), the left ureter was catheterized for urine collection, while simultaneously blood access was achieved. Rats received an intravenous (i.v.) infusion of either 1) hypertonic glucose to maintain blood glucose at 20-25 mM (G; n=8); 2) hypertonic glucose as in 1) and a Rho-A-kinase inhibitor (Y-27632; Rho-G; n=8); 3) 20% mannitol (MANN; n=7), or 4) hypertonic (12%) NaCl to maintain plasma crystalloid osmotic pressure (picry) at ~320-325 mOsm/l (NaCl; n=8); 5) physiologic saline (SHAM; n=8). Fluorescein isothiocyanate (FITC)-Ficoll 70/400 was infused i.v. for at least 20 min before terminating the experiments, and plasma and urine collected to determine the glomerular sieving coefficients () for polydisperse Ficoll (mol. radius 15-80A) by high performance size exclusion chromatography. In G there was a marked increase in for Ficoll55-80A at 20 min, which was completely reversible within 60 min and abrogated by a Rho-kinase (ROCK) inhibitor, while glomerular permeability remained unchanged in MANN and NaCl. In conclusion, acute HG caused rapid, reversible increases in for large Ficolls, not related to the concomitant hyperosmolarity, but sensitive to ROCK inhibition. The changes observed were consistent with the formation of an increased number of large pores in the glomerular filter. The sensitivity of the permeability changes to ROCK inhibition strongly indicates that the cytoskeleton of the cells in the glomerular barrier be involved in these alterations. Key words: microalbuminuria, Rho-A-kinase, podocytes, endothelium.
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| 5. |
- Axelsson, Josefin, et al.
(författare)
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Effects of early endotoxemia and dextran-induced anaphylaxis on the size-selectivity of the glomerular filtration barrier in rats.
- 2009
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Ingår i: American Journal of Physiology: Renal, Fluid and Electrolyte Physiology. - : American Physiological Society. - 0363-6127. ; 296:2, s. 242-248
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Tidskriftsartikel (refereegranskat)abstract
- This study was performed to investigate the glomerular permeability alterations responsible for the microalbuminuria occurring in endotoxemia and during anaphylactic shock. In anaesthetized Wistar rats, the left ureter was catheterized for urine collection, while simultaneously, blood access was achieved. Endotoxemia was induced by Lipopolysaccharide (LPS) from E. Coli, and glomerular permeability assessed at 60, 90 (ENDO-(60)/90; n=7) and 120 min (ENDO-120; n=7). Anaphylaxis was induced by a bolus dose of Dextran-70, and glomerular permeability assessed at 5 min (ANA-5; n=8) and 40 min (ANA-40; n=9). Sham animals, were followed for either 5 or 120 min. The glomerular sieving coefficients () to FITC-Ficoll (70/400) were determined from plasma and urine samples and assessed using size-exclusion chromatography (HPLC). 2 h after start of the LPS infusion, but not at 60 or 90 min, for Ficoll70A had increased markedly (from 2.91 x 10(-5) +/- 6.33 x 10(-6) to 7.78 x 10(-5) +/- 6.21 x 10(-6) (P<0.001)). In anaphylaxis there was a large increase in for Ficolls >60 A in mol. radius already at 5 min, but the glomerular permeability was completely restored at 40 min. In conclusion, there was a transient, immediate increment of glomerular permeability in dextran-induced anaphylaxis, which was completely reversible within 40 min. By contrast, endotoxemia caused an increase in glomerular permeability that was manifest first after 2 h. In both cases to large Ficoll molecules were markedly increased, reflecting an increase in the number of large pores in the glomerular filter. Key words: capillary permeability, Ficoll, sieving coefficient, albumin.
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| 6. |
- Axelsson, Josefin, et al.
(författare)
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Loss of size-selectivity of the glomerular filtration barrier in rats following laparotomy and muscle trauma.
- 2009
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Ingår i: American Journal of Physiology: Renal, Fluid and Electrolyte Physiology. - : American Physiological Society. - 0363-6127. ; 297, s. 577-582
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Tidskriftsartikel (refereegranskat)abstract
- Post-traumatic microalbuminuria may be caused by either charge- or size-selective alterations in the glomerular filtration barrier, or both, and/or to a reduction in proximal tubular protein reabsorption (PTR). This study was performed to elucidate the pathophysiology of the increases in glomerular permeability occurring in rats exposed to laparotomy or to laparotomy and muscle trauma. In anaesthetized Wistar rats (250-280 g), the left ureter was catheterized for urine collection, while simultaneously blood access was achieved. Rats were exposed to trauma by laparotomy (L) (n=8), or by a combination of L and muscle trauma (MT), induced by topical blunt injury of the abdominal muscles bilaterally. After L muscles were crushed using a hemostatic forceps at either 2x2 sites ("small" MT; n=9), or at 2x5 sites ("large" MT; n=9). Sham groups (n=16), not exposed to laparotomy, were used as controls. The glomerular sieving coefficients () to polydisperse, fluorescein isothiocyanate (FITC)-Ficoll-70/400 (mol.radius 13-80A) were determined at 5 or 60 min after L and (L + MT), respectively, from plasma and urine samples, and analyzed by high performance size-exclusion chromatography (HPSEC). A tissue uptake technique was used to assess for (125)I-serum albumin. L, with or without MT, increased for Ficoll55-80A and albumin rapidly and markedly. -Ficoll70A thus increased approximately threefold, and for albumin significantly, for all trauma groups. According to the "two-pore model" of glomerular permeability these changes reflect an increase in the number of large pores in the glomerular filter without any primary changes in the charge-selective properties of the filter. Key words: microalbuminuria, glomerular sieving coefficients, albumin, Ficoll.
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| 7. |
- Axelsson, Josefin, et al.
(författare)
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mTOR inhibition with temsirolimus causes acute increases in glomerular permeability, but inhibits the dynamic permeability actions of puromycin aminonucleoside.
- 2015
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Ingår i: American Journal of Physiology-Renal Physiology. - : American Physiological Society. - 1522-1466 .- 1931-857X. ; 308:10, s. 1056-1064
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Tidskriftsartikel (refereegranskat)abstract
- Inhibitors of the mammalian target of rapamycin (mTORi) can produce de novo proteinuria in kidney transplant patients. On the other hand, mTORi has been shown to suppress disease progression in several animal models of kidney disease. In the present study we investigated whether glomerular permeability can be acutely altered by the mTORi, temsirolimus, and whether mTORi can affect acute purumycin aminonucleoside (PAN) or angiotensin II (AngII) induced glomerular hyperpermeability. In anaesthetized Wistar rats, the left ureter was cannulated for urine collection, while simultaneously, blood access was achieved. Temsirolimus was administered as a single dose i.v. 30 min before the start of the experiments in animals infused with PAN or AngII or in non-exposed animals. Polydispersed FITC-Ficoll-70/400 (mol.radius 10-80Å) and (51)Cr-EDTA infusion was given during the whole experiment. Measurements of Ficoll in plasma and urine were performed sequentially before the temsirolimus injection (baseline) and at 5, 15, 30, 60 and 120 min after the start of the experiments. Urine and plasma samples were analyzed by high performance size exclusion chromatography (HPSEC) to assess glomerular sieving coefficients (θ) for Ficoll10-80Å. Temsirolimus per se increased baseline glomerular permeability to Ficoll50-80Å 45 min after its administration, a ROS dependent phenomenon. PAN caused a rapid and reversible increase in glomerular permeability, peaking at 5 min, and again at 60-120 min, which could be blocked by the ROS scavenger, tempol. mTORi abrogated the second permeability peak induced by PAN. However, it had no effect on the immediate AngII or PAN induced increases in glomerular permeability.
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| 8. |
- Axelsson, Josefin, et al.
(författare)
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Rapid, dynamic changes in glomerular permeability to macromolecules during systemic Angiotensin II (AngII) infusion in rats.
- 2012
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Ingår i: American Journal of Physiology-Renal Physiology. - : American Physiological Society. - 1522-1466 .- 1931-857X. ; 303:6, s. 790-799
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Tidskriftsartikel (refereegranskat)abstract
- The actions of systemic angiotensin II (AngII) infusions on glomerular permeability were investigated in vivo. In anaesthetized Wistar rats (250-280g) the left ureter was cannulated for urine collection, while simultaneously blood access was achieved. Rats were continuously infused i.v. with either of four doses of AngII (16 ng/kg/min (Lo-AngII; n=7), 230 ng/kg/min (Lo-Int-AngII; n=8), 910 ng/kg/min (Hi-Int-AngII; n=7), or 1.82 μg/kg/min (Hi-AngII; n=8)), or with the calcium channel blocker, nimodipine, together with the Hi-Int-AngII dose (n=6), respectively, and with polydisperse fluorescein isothiocyanate (FITC)-Ficoll-70/400 (mol.radius 10-80Å) and (51)Cr-EDTA. Plasma and urine samples were taken at 5, 15, 30, 60 and 120 min and analyzed by high performance size exclusion chromatography (HPSEC) for determination of glomerular sieving coefficients (θ) to Ficoll. Mean arterial pressure (MAP) and glomerular filtration rate (GFR) were also assessed. In AngII groups there was a rapid, marked increase in glomerular permeability (θ) to Ficoll molecules >34Å, which was completely abrogated by the AngII-blocker, candesartan. The permeability increase was reversible within 15-60 min, but some increases remained even after 60 min. For the highest AngII doses given GFR decreased transiently, concomitant with marked increases in MAP. Nimodipine blocked the hemodynamic AngII actions, whereas the glomerular permeability response remained unchanged. According to a two-pore model and a log-normal distributed pore model the AngII induced increases in glomerular permeability are compatible with an increased number of "large pores" in the glomerular filter, and, to some extent, an increase in the dispersity of the small pore radius.
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| 9. |
- Axelsson, Josefin, et al.
(författare)
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Reduced diffusion of charge-modified, conformationally intact anionic Ficoll relative to neutral Ficoll across the rat glomerular filtration barrier in vivo
- 2011
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Ingår i: American Journal of Physiology-Renal Physiology. - : American Physiological Society. - 1522-1466 .- 1931-857X. ; 301:4, s. 708-712
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Tidskriftsartikel (refereegranskat)abstract
- Axelsson J, Sverrisson K, Rippe A, Fissell W, Rippe B. Reduced diffusion of charge-modified, conformationally intact anionic Ficoll relative to neutral Ficoll across the rat glomerular filtration barrier in vivo. Am J Physiol Renal Physiol 301: F708-F712, 2011. First published July 20, 2011; doi:10.1152/ajprenal.00183.2011.-The glomerular filtration barrier (GFB) is commonly conceived as a negatively charged sieve to proteins. Recent studies, however, indicate that glomerular charge effects are small for anionic, carboxymethylated (CM) dextran vs. neutral dextran. Furthermore, two studies assessing the glomerular sieving coefficients (theta) for negative CM-Ficoll vs. native Ficoll have demonstrated an increased glomerular permeability for CM-Ficoll (Asgeirsson D, Venturoli D, Rippe B, Rippe C. Am J Physiol Renal Physiol 291: F1083-F1089, 2006; Guimaraes M, Nikolovski J, Pratt L, Greive K, Comper W. Am Physiol Renal Physiol 285: F1118-F1124, 2003.). The CM-Ficoll used, however, showed a larger Stokes-Einstein radius (a(e)) than neutral Ficoll, and it was proposed that the introduction of negative charges in the Ficoll molecule had made it more flexible and permeable. Recently, a negative FITC-labeled CM-Ficoll (CMI-Ficoll) was produced with a conformation identical to that of neutral FITC-Ficoll. Using these probes, we determined their theta:s in anesthetized Wistar rats (259 +/- 2.5 g). After blood access had been achieved, the left ureter was cannulated for urine sampling. Either polysaccharide was infused (iv) together with a filtration marker, and urine and plasma were collected. Assessment of theta FITC-Ficoll was achieved by high-performance size-exclusion chromatography (HPSEC). CMI-Ficoll and native Ficoll had identical elugrams on the HPSEC. Diffusion of anionic Ficoll was significantly reduced compared with that of neutral Ficoll across the GFB for molecules of a(e) similar to 20-35 angstrom, while there were no charge effects for Ficoll of a(e) similar to 35-80 angstrom. The data are consistent with a charge effect present in "small pores," but not in "large pores," of the GFB and mimicked those obtained for anionic membranes in vitro for the same probes.
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| 10. |
- Axelsson, Josefin, et al.
(författare)
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Scavengers of reactive oxygen species, paracalcitol, RhoA and Rac-1 inhibitors and tacrolimus inhibit angiotensin II induced actions on glomerular permeability.
- 2013
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Ingår i: American Journal of Physiology-Renal Physiology. - : American Physiological Society. - 1522-1466 .- 1931-857X. ; 305:3, s. 237-243
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Tidskriftsartikel (refereegranskat)abstract
- Systemic infusions of angiotensin II (AngII) rapidly induce large, dynamic increases in the permeability of the glomerular filtration barrier (GFB) in rats. After binding to its receptor(s), AngII generates reactive oxygen species (ROS) and produces Ca(2+) influx into cells, leading to activation of a plethora of signaling cascades, including e.g. calcineurin, and small GTPases, such as Rac-1 and RhoA. In the present study we sought to interact with some of these cascades in order to test potential novel antiproteinuric agents. In anaesthetized Wistar rats the left urether was cannulated for urine collection, and blood access was achieved. Rats were infused with AngII (16 ng/kg/min) alone, or together with the ROS scavengers, TEMPOL or dimethylthiourea (DMTU), or the D-vitamin analog, paracalcitol, the RhoA-kinase inhibitor, Y-27632, the Rac-1 inhibitor, NSC-23766, or the calcineurin inhibitor, tacrolimus. FITC-Ficoll-70/400 (mol.radius 10-80Å) and (51)Cr-EDTA were infused throughout the experiment. Plasma and urine samples were taken during baseline and at 5 and 15 min after the start of the infusions and analyzed by high performance size exclusion chromatography (HPSEC) for determination of glomerular sieving coefficients (θ) for Ficoll10-80Å. AngII infusion into rats caused marked increases in glomerular permeability to large Ficoll molecules (Ficoll50-80Å), which were abrogated by the ROS scavenger TEMPOL and partly by DMTU. Paracalcitol, RhoA and Rac-1 inhibition, and, to some extent, tacrolimus, but not prostacyclin, could also inhibit the glomerular permeability actions of AngII. Our data suggest that cellular ROS generation and active Ca(2+) signaling are involved in AngII induced increases in glomerular permeability.
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