A hydrodynamical study of the flow in renal tubules

The hydrodynamical problem of flow in proximal renal tubule is investigated by considering axisymmetric flow of a viscous, incompressible fluid through a long narrow tube of varying cross-section with reabsorption at the wall. Two cases for reabsorption have been studied (i) when the bulk flow,Q, decays exponentially with the axial distancex, and (ii) whenQ is an arbitrary function ofx such thatQ-Q 0 can be expressed as a Fourier integral (whereQ 0 is the flux atx=0). The analytic expressions for flow variables have been obtained by applying perturbation method in terms of wall parameter ε. The effects of ε on pressure drop across the tube, radial velocity and wall shear have been studied in the case of exponentially decaying bulk flow and it has been found that the results are in agreement with the existing ones for the renal tubules.

Effect of renoguanylin on hydrogen/bicarbonate ion transport in rat renal tubules

Renoguanylin (REN) is a recently described member of the guanylin family, which was first isolated from eels and is expressed in intestinal and specially kidney tissues. In the present work we evaluate the effects of REN on the mechanisms of hydrogen transport in rat renal tubules by the stationary microperfusion method. We evaluated the effect of 1 mu M and 10 mu M of renoguanylin (REN) on the reabsorption of bicarbonate in proximal and distal segments and found that there was a significant reduction in bicarbonate reabsorption. In proximal segments, REN promoted a significant effect at both 1 and 10 mu M concentrations. Comparing control and REN concentration of 1 mu M, JHCO(3)(-) . nmol cm(-2) s(-1) -1,76 +/- 0.11(control) x 1,29 +/- 0,08(REN) 10 mu m: P<0.05, was obtained. In distal segments the effect of both concentrations of REN was also effective, being significant e.g. at a concentration of 1 mu M (JHCO(3)(-), nmol cm(-2) s(-1) -0.80 +/- 0.07(control) x 0.60 +/- 0.06(REN) 1 mu m; P<0.05), although at a lower level than in the proximal tubule. Our results suggest that the action of REN on hydrogen transport involves the inhibition of Na(+)/H(+) exchanger and H(+)-ATPase in the luminal membrane of the perfused tubules by a PKG dependent pathway. (c) 2009 Elsevier B.V. All rights reserved.

Effect of uroguanylin on potassium and bicarbonate transport in rat renal tubules

The effect of uroguanylin (UGN) oil K(+) and H(+) secretion in the renal tubules of the rat kidney was studied using in vivo stationary microperfusion. For the study of K(+) secretion, a tubule was Punctured to inject a column of FDC-green-colored Ringer's solution with 0.5 mmol KCI/L 10(-6)(mol UGN/L, and oil was Used to block fluid flow. K(+) activity and transepithelial potential differences (PD) were measured with double microelectrodes (K(+) ion-selective resin vs. reference) in the distal tubules of the same nephron. During perfusion, K(+) activity rose exponentially, from 0.5 mmol/L to stationary concentration, allowing for the calculation of K(+) secretion J(K)). JK increased from 0.63 +/- 0.06 nmol.cm(-2).s(-1) in the control croup to 0.85 +/- 0.06 in the UGN group (p < 0.01). PD was -51.0 +/- 5.3 mV in the control group and -50.3 +/- 4.98 mV in the UGN group. In the presence of 10(-7) mol iberiotoxin/L, the UGN effect was abolished: JK was 0.37 +/- 0.038 nmol-cm(-2).s(-1) in the absence of, and 0.38 +/- 0.025 in the presence of, UGN. indicating its action oil rnaxi-K channels. In another series of experiments, renal tubule acidification was studied, using similar method: proximal and distal tubules were perfused with solutions containing 25 mmol NaHCO(3)/L. Acidification half-time was increased both in proximal and distal segments and, as a consequence, bicarbonate reabsorption decreased in the presence of UGN (in proximal tubules, from 2.40 +/- 0.26 to 1.56 +/- 0.21 nmol-cm(-2).s(-1)). When the Na(+)/H(+) exchanger was inhibited by 10(-4) mol hexamethylene amiloride (HMA)/L, the control and UGN groups were not significantly different. In the late distal tubule, after HMA, UGN significantly reduced J(HCO3)(-). indicating all effect of UGN oil H(+)-ATPase. These data show that UGN stimulated J(K)(+) by actin, oil maxi-K channels. and decreased J(HCO3)(-) by acting on NHE3 in proximal and H(+)-ATPase in distal tubules.

Effect of renoguanylin on hydrogen/bicarbonate ion transport in rat renal tubules

Renoguanylin (REN) is a recently described member of the guanylin family, which was first isolated from eels and is expressed in intestinal and specially kidney tissues. In the present work we evaluate the effects of REN on the mechanisms of hydrogen transport in rat renal tubules by the stationary microperfusion method. We evaluated the effect of 1 mu M and 10 mu M of renoguanylin (REN) on the reabsorption of bicarbonate in proximal and distal segments and found that there was a significant reduction in bicarbonate reabsorption. In proximal segments, REN promoted a significant effect at both 1 and 10 mu M concentrations. Comparing control and REN concentration of 1 mu M, JHCO(3)(-) . nmol cm(-2) s(-1) -1,76 +/- 0.11(control) x 1,29 +/- 0,08(REN) 10 mu m: P<0.05, was obtained. In distal segments the effect of both concentrations of REN was also effective, being significant e.g. at a concentration of 1 mu M (JHCO(3)(-), nmol cm(-2) s(-1) -0.80 +/- 0.07(control) x 0.60 +/- 0.06(REN) 1 mu m; P<0.05), although at a lower level than in the proximal tubule. Our results suggest that the action of REN on hydrogen transport involves the inhibition of Na(+)/H(+) exchanger and H(+)-ATPase in the luminal membrane of the perfused tubules by a PKG dependent pathway. (c) 2009 Elsevier B.V. All rights reserved.

Renal tubular NEDD4-2 deficiency causes NCC-mediated salt-dependent hypertension.

The E3 ubiquitin ligase NEDD4-2 (encoded by the Nedd4L gene) regulates the amiloride-sensitive epithelial Na+ channel (ENaC/SCNN1) to mediate Na+ homeostasis. Mutations in the human β/γENaC subunits that block NEDD4-2 binding or constitutive ablation of exons 6-8 of Nedd4L in mice both result in salt-sensitive hypertension and elevated ENaC activity (Liddle syndrome). To determine the role of renal tubular NEDD4-2 in adult mice, we generated tetracycline-inducible, nephron-specific Nedd4L KO mice. Under standard and high-Na+ diets, conditional KO mice displayed decreased plasma aldosterone but normal Na+/K+ balance. Under a high-Na+ diet, KO mice exhibited hypercalciuria and increased blood pressure, which were reversed by thiazide treatment. Protein expression of βENaC, γENaC, the renal outer medullary K+ channel (ROMK), and total and phosphorylated thiazide-sensitive Na+Cl- cotransporter (NCC) levels were increased in KO kidneys. Unexpectedly, Scnn1a mRNA, which encodes the αENaC subunit, was reduced and proteolytic cleavage of αENaC decreased. Taken together, these results demonstrate that loss of NEDD4-2 in adult renal tubules causes a new form of mild, salt-sensitive hypertension without hyperkalemia that is characterized by upregulation of NCC, elevation of β/γENaC, but not αENaC, and a normal Na+/K+ balance maintained by downregulation of ENaC activity and upregulation of ROMK.

Expression of renin-angiotensin system signalling compounds in maternal protein-restricted rats: effect on renal sodium excretion and blood pressure

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Efeitos da ciclosporina a sobre a função renal de cães da raça Golden Retriever normais ou afetados pela distrofia muscular

The muscular dystrophy of Golden Retriever is a degenerative miopaty caused by the absence of dystrophy and it is genetically homologue of the Duchenne muscular dystrophy in humans, so, these dogs are considerably experimental models for studies on cellular therapy. Their successful depends of the adequate immunosuppression. Cyclosporin A is indicated for that and the monitoring of blood concentration and adverse effects are essential to viabilise the therapy. It was studied GRMD dogs, and normal dogs from the same breed, submitted for therapy with CsA, associated, on GRMD, of cell transplantation. It was evaluated the possible effects of the drug on renal functions. It has been considerate the clinic manifestations, urinalisis, testis of glomerular function and blood concentrations of urea, cretinine, sodium and potassium. In our results we found a discrete increase of blood urea on booth groups; increased levels of urine's cylinders and protein and also increase of urinary density on GRMD group. CsA therapy could make acute lesions on renal tubules, especially on GRMD. These dogs also have different reactions than normal dogs on relation of ions homeostasis and renal function. However, earlier diagnosis and adequate treatment could prevent the development of renal diseases.

Uromodulin is expressed in renal primary cilia and UMOD mutations result in decreased ciliary uromodulin expression

Uromodulin (UMOD) mutations are responsible for three autosomal dominant tubulo-interstitial nephropathies including medullary cystic kidney disease type 2 (MCKD2), familial juvenile hyperuricemic nephropathy and glomerulocystic kidney disease. Symptoms include renal salt wasting, hyperuricemia, gout, hypertension and end-stage renal disease. MCKD is part of the 'nephronophthisis-MCKD complex', a group of cystic kidney diseases. Both disorders have an indistinguishable histology and renal cysts are observed in either. For most genes mutated in cystic kidney disease, their proteins are expressed in the primary cilia/basal body complex. We identified seven novel UMOD mutations and were interested if UMOD protein was expressed in the primary renal cilia of human renal biopsies and if mutant UMOD would show a different expression pattern compared with that seen in control individuals. We demonstrate that UMOD is expressed in the primary cilia of renal tubules, using immunofluorescent studies in human kidney biopsy samples. The number of UMOD-positive primary cilia in UMOD patients is significantly decreased when compared with control samples. Additional immunofluorescence studies confirm ciliary expression of UMOD in cell culture. Ciliary expression of UMOD is also confirmed by electron microscopy. UMOD localization at the mitotic spindle poles and colocalization with other ciliary proteins such as nephrocystin-1 and kinesin family member 3A is demonstrated. Our data add UMOD to the group of proteins expressed in primary cilia, where mutations of the gene lead to cystic kidney disease.

Mutations in the tight-junction gene claudin 19 (CLDN19) are associated with renal magnesium wasting, renal failure, and severe ocular involvement

Claudins are major components of tight junctions and contribute to the epithelial-barrier function by restricting free diffusion of solutes through the paracellular pathway. We have mapped a new locus for recessive renal magnesium loss on chromosome 1p34.2 and have identified mutations in CLDN19, a member of the claudin multigene family, in patients affected by hypomagnesemia, renal failure, and severe ocular abnormalities. CLDN19 encodes the tight-junction protein claudin-19, and we demonstrate high expression of CLDN19 in renal tubules and the retina. The identified mutations interfere severely with either cell-membrane trafficking or the assembly of the claudin-19 protein. The identification of CLDN19 mutations in patients with chronic renal failure and severe visual impairment supports the fundamental role of claudin-19 for normal renal tubular function and undisturbed organization and development of the retina.

Origin of renal myofibroblasts in the model of unilateral ureter obstruction in the rat

Tubulo-interstitial fibrosis is a constant feature of chronic renal failure and it is suspected to contribute importantly to the deterioration of renal function. In the fibrotic kidney there exists, besides normal fibroblasts, a large population of myofibroblasts, which are supposedly responsible for the increased production of intercellular matrix. It has been proposed that myofibroblasts in chronic renal failure originate from the transformation of tubular cells via epithelial-mesenchymal transition (EMT) or from infiltration by bone marrow-derived precursors. Little attention has been paid to the possibility of a transformation of resident fibroblasts into myofibroblasts in renal fibrosis. Therefore we examined the fate of resident fibroblasts in the initial phase of renal fibrosis in the classical model of unilateral ureter obstruction (UUO) in the rat. Rats were perfusion-fixed on days 1, 2, 3 and 4 after ligature of the right ureter. Starting from 1 day of UUO an increasing expression of alpha-smooth muscle actin (alphaSMA) in resident fibroblasts was revealed by immunofluorescence and confirmed by the observation of bundles of microfilaments and webs of intermediate filaments in the electron microscope. Inversely, there was a decreased expression of 5'-nucleotidase (5'NT), a marker of renal cortical fibroblasts. The RER became more voluminous, suggesting an increased synthesis of matrix. Intercellular junctions, a characteristic feature of myofibroblasts, became more frequent. The mitotic activity in fibroblasts was strongly increased. Renal tubules underwent severe regressive changes but the cells retained their epithelial characteristics and there was no sign of EMT. In conclusion, after ureter ligature, resident peritubular fibroblasts proliferated and they showed progressive alterations, suggesting a transformation in myofibroblasts. Thus the resident fibroblasts likely play a central role in fibrosis in that model.

GABARAP deficiency modulates expression of NaPi-IIa in renal brush-border membranes

Renal reabsorption of inorganic phosphate (P(i)) is mainly mediated by the Na(+)-dependent P(i)-cotransporter NaPi-IIa that is expressed in the brush-border membrane (BBM) of renal proximal tubules. Regulation and apical expression of NaPi-IIa are known to depend on a network of interacting proteins. Most of the interacting partners identified so far associate with the COOH-terminal PDZ-binding motif (TRL) of NaPi-IIa. In this study GABA(A) receptor-associated protein (GABARAP) was identified as a novel interacting partner of NaPi-IIa applying a membrane yeast-two-hybrid system (MYTH 2.0) to screen a mouse kidney library with the TRL-truncated cotransporter as bait. GABARAP mRNA and protein are present in renal tubules, and the interaction of NaPi-IIa and GABARAP was confirmed by using glutathione S-transferase pulldowns from BBM and coimmunoprecipitations from transfected HEK293 cells. Amino acids 36-68 of GABARAP were identified as the determinant for the described interaction. The in vivo effects of this interaction were studied in a murine model. GABARAP(-/-) mice have reduced urinary excretion of P(i), higher Na(+)-dependent (32)P(i) uptake in BBM vesicles, and increased expression of NaPi-IIa in renal BBM compared with GABARAP(+/+) mice. The expression of Na(+)/H(+) exchanger regulatory factor (NHERF)1, an important scaffold for the apical expression of NaPi-IIa, is also increased in GABARAP(-/-) mice. The absence of GABARAP does not interfere with the regulation of the cotransporter by either parathyroid hormone or acute changes of dietary P(i) content.

Renal structural and functional repair in a mouse model of reversal of ureteral obstruction

The end point of immune and nonimmune renal injury typically involves glomerular and tubulointerstitial fibrosis. Although numerous studies have focused on the events that lead to renal fibrosis, less is known about the mechanisms that promote cellular repair and tissue remodeling. Described is a model of renal injury and repair after the reversal of unilateral ureteral obstruction (UUO) in male C57b1/6J mice. Male mice (20 to 25 g) underwent 10 d of UUO with or without 1, 2, 4, or 6 wk of reversal of UUO (R-UUO). UUO resulted in cortical tubular cell atrophy and tubular dilation in conjunction with an almost complete ablation of the outer medulla. This was associated with interstitial macrophage infiltration; increased hydroxyproline content; and upregulated type I, III, IV, and V collagen expression. The volume density of kidney occupied by renal tubules that exhibited a brush border was measured as an assessment of the degree of repair after R-UUO. After 6 wk of R-UUO, there was an increase in the area of kidney occupied by repaired tubules (83.7 +/- 5.9%), compared with 10 d UUO kidneys (32.6 +/- 7.3%). This coincided with reduced macrophage numbers, decreased hydroxyproline content, and reduced collagen accumulation and interstitial matrix expansion, compared with obstructed kidneys from UUO mice. GFR in the 6-wk R-UUO kidneys was restored to 43 to 88% of the GFR in the contralateral unobstructed kidneys. This study describes the regenerative potential of the kidney after the established interstitial matrix expansion and medullary ablation associated with UUO in the adult mouse.

CIC-5: A chloride channel with multiple roles in renal tubular albumin uptake

CIC-5 is a chloride (Cl-) channel expressed in renal tubules and is critical for normal tubular function. Loss of function nonsense or missense mutations in CIC-5 are associated with Dent's disease, a condition in which patients present with low molecular weight (LMW) proteinuria (including albuminuria), hypercalciuria and nephrolithiasis. Several key studies in CIC-5 knockout mice have shown that the proteinuria results from defective tubular reabsorption of proteins. CIC-5 is typically regarded as an intracellular Cl- channel and thus the defect in this receptor-mediated uptake pathway was initially attributed to the failure of the early endosomes to acidify correctly. CIC-5 was postulated to play a key role in transporting the Cl- ions required to compensate for the movement of H+ during endosomal acidification. However, more recent studies suggest additional roles for CIC-5 in the endocytosis of albumin. CIC-5 is now known to be expressed at low levels at the cell surface and appears to be a key component in the assembly of the macromolecular complex involved in protein endocytosis. Furthermore, mutations in CIC-5 affect the trafficking of v-H+-ATPase and result in decreased expression of the albumin receptor megalin/cubulin. Thus, the expression of CIC-5 at the cell surface as well as its presence in endosomes appears to be essential for normal protein uptake by the renal proximal tubule. (c) 2005 Elsevier Ltd. All rights reserved.

复方治疗慢性肾衰海洋新药的初步研究

该论文在褐藻多糖硫酸酯已有研究工作的基础上,参考中药治肾病领域有关文献,结合中医药理论,组方成治疗慢性肾衰复方海洋新药-复方褐藻多糖硫酸酯,并进行了复方褐藻多糖硫酸酯的部分药学、初步药效学和急性毒性试验的研究.

Tracking down the cause of proteinuria in primary care

Proteinuria originates from the kidney and occurs as a result of injury to either the glomerulus or the renal tubule or both. It is relatively common in the general population with reported point prevalence of up to 8% but the prevalence falls to around 2% on repeated testing. Chronic glomerular injury resulting in proteinuria may be secondary to prolonged duration of diabetes or hypertension. A tubular origin of proteinuria may be associated with inflammation of renal tubules triggered by prescribed drugs or ingested toxins. In the absence of obvious clues to the cause of persistent proteinuria on history or clinical examination it is worthwhile reviewing the patient's prescribed drugs to identify any potentially nephrotoxic agents e.g. NSAIDs. NICE guidelines recommend screening for proteinuria in individuals at higher risk for chronic kidney disease (CKD). These include patients with diabetes, hypertension, cardiovascular disease, connective tissue disorders, a family history of renal disease and those prescribed potentially nephrotoxic drugs. Patients with sudden onset of lower limb oedema and associated proteinuria should have a serum albumin level measured to exclude the nephrotic syndrome. Renal tract ultrasound will measure kidney size, and detect scarring associated with chronic pyelonephritis or prior renal stone disease which can cause proteinuria.