scholarly journals Substructure of the glomerular slit diaphragm in freeze-fractured normal rat kidney

1975 ◽  
Vol 65 (1) ◽  
pp. 233-236 ◽  
Author(s):  
MJ Karnovsky ◽  
GB Ryan
Keyword(s):  
Plasma Proteins ◽  
Plasma Membranes ◽  
Rat Kidney ◽  
Slit Diaphragm ◽  
Renal Glomerulus ◽  
Regular Array ◽  
Filtration Barrier ◽  
Normal Rat ◽  
Cross Bridges

In the renal glomerulus, the narrow slits between adjacent epithelial podocytes are bridged by a diaphragm (2, 8, 11). In rat and mouse kidneys fixed by perfusion with tannic acid and glutaraldehyde (TAG), it has recently been discovered that this diaphragm has a highly ordered, isoporous substructure (9). It consists of a regular array of alternating cross bridges extending from the podocyte plasma membranes to a centrally running filament. This zipperlike pattern results in two rows of rectangular pores, approximately 40 X 140 A in cross section, dimensions consistent with the proposed role of the diaphragm as an important filtration barrier to plasma proteins (6). In the present study, we found in freeze-cleaved and in freeze-etched normal rat glomeruli that the surface of the slit diaphragm has an appearance conforming to the pattern found in sectioned material.

scholarly journals POROUS SUBSTRUCTURE OF THE GLOMERULAR SLIT DIAPHRAGM IN THE RAT AND MOUSE

1974 ◽  
Vol 60 (2) ◽  
pp. 423-433 ◽  
Author(s):  
Richard Rodewald ◽  
Morris J. Karnovsky
Keyword(s):  
Serum Albumin ◽  
Plasma Membranes ◽  
Total Surface Area ◽  
Slit Diaphragm ◽  
Physiological Data ◽  
Filtration Barrier ◽  
Central Filament ◽  
Cross Bridges ◽  
Tracer Experiments ◽  
Glomerular Capillaries

The highly ordered, isoporous substructure of the glomerular slit diaphragm was revealed in rat and mouse kidneys fixed by perfusion with tannic acid and glutaraldehyde. The slit diaphragm was similar in both animal species and appeared as a continuous junctional band, 300–450 Å wide, consistently present within all slits formed by the epithelial foot processes. The diaphragm exhibited a zipper-like substructure with alternating, periodic cross bridges extending from the podocyte plasma membranes to a central filament which ran parallel to and equidistant from the cell membranes. The dimensions and spacing of the cross bridges defined a uniform population of rectangular pores approximately 40 by 140 Å in cross section and 70 Å in length. The total area of the pores was calculated to be about 2–3% of the total surface area of the glomerular capillaries. Physiological data indicate that the glomerular filter functions as if it were an isoporous membrane which excludes proteins larger than serum albumin. The similarity between the dimensions of the pores in the slit diaphragm and estimates for the size and shape of serum albumin supports the conclusion from tracer experiments that the slit diaphragm may serve as the principal filtration barrier to plasma proteins in the kidney.

scholarly journals Early Glomerular Filtration Defect and Severe Renal Disease in Podocin-Deficient Mice

2004 ◽  
Vol 24 (2) ◽  
pp. 550-560 ◽  
Author(s):  
Séverine Roselli ◽  
Laurence Heidet ◽  
Mireille Sich ◽  
Anna Henger ◽  
Matthias Kretzler ◽  
...  
Keyword(s):  
Renal Disease ◽  
Glomerular Filtration ◽  
Molecular Mechanisms ◽  
Slit Diaphragm ◽  
Vascular Lesions ◽  
Suitable Model ◽  
Glomerular Diseases ◽  
Filtration Barrier ◽  
Severe Renal Disease

ABSTRACT Podocytes are specialized epithelial cells covering the basement membrane of the glomerulus in the kidney. The molecular mechanisms underlying the role of podocytes in glomerular filtration are still largely unknown. We generated podocin-deficient (Nphs2 −/−) mice to investigate the function of podocin, a protein expressed at the insertion of the slit diaphragm in podocytes and defective in a subset of patients with steroid-resistant nephrotic syndrome and focal and segmental glomerulosclerosis. Nphs2 −/− mice developed proteinuria during the antenatal period and died a few days after birth from renal failure caused by massive mesangial sclerosis. Electron microscopy revealed the extensive fusion of podocyte foot processes and the lack of a slit diaphragm in the remaining foot process junctions. Using real-time PCR and immunolabeling, we showed that the expression of other slit diaphragm components was modified in Nphs2 −/− kidneys: the expression of the nephrin gene was downregulated, whereas that of the ZO1 and CD2AP genes appeared to be upregulated. Interestingly, the progression of the renal disease, as well as the presence or absence of renal vascular lesions, depends on the genetic background. Our data demonstrate the crucial role of podocin in the establishment of the glomerular filtration barrier and provide a suitable model for mapping and identifying modifier genes involved in glomerular diseases caused by podocyte injuries.

Ischemia-induced cleavage of cadherins in NRK cells: evidence for a role of metalloproteinases

2005 ◽  
Vol 289 (2) ◽  
pp. F280-F288 ◽  
Author(s):  
Marisa D. Covington ◽  
Kayla J. Bayless ◽  
Robert C. Burghardt ◽  
George E. Davis ◽  
Alan R. Parrish
Keyword(s):  
Protein Expression ◽  
Glucose Transporter ◽  
Rat Kidney ◽  
Ischemia Reperfusion ◽  
Cell Number ◽  
Tissue Inhibitors Of Metalloproteinases ◽  
Glucose Transporter 1 ◽  
Normal Rat ◽  
E Cadherin

Although ischemia has been shown to disrupt cell adhesion, the underlying molecular mechanism is unknown. In these studies, we adapted a model of ischemia-reperfusion to normal rat kidney (NRK) cells, examined disruption of the cadherin/catenin complex, and identified a role for matrix metalloproteinases (MMPs) in ischemia-induced cleavage of cadherins. In NRK cells, ischemia was induced by applying a thin layer of PBS solution supplemented with calcium and magnesium and a layer of mineral oil, which restricts exposure to oxygen. NRK cells exhibited extracellular 80-kDa and intracellular 40-kDa E-cadherin fragments after 4 h of ischemia, and at 6 h the expression of full-length E-cadherin decreased. While no fragments of N-cadherin, α-catenin, and γ-catenin were observed at any time point, the detectable levels of these proteins decreased during ischemia. Ischemia was detected by an increase in pimonidazole adducts, as well as an increase in glucose transporter-1 protein expression. Ischemia did not decrease cell number, but there was a decrease in ATP levels. In addition, there was no evidence of cleaved caspase 3 or 9 during 6 h of ischemia. The MMP inhibitors GM-6001 and TAPI-O inhibited cleavage and/or loss of E- and N-cadherin protein expression. Tissue inhibitors of metalloproteinases (TIMP)-3 and to a lesser extent TIMP-2, but not TIMP-1, inhibit ischemic cleavage and/or loss of E- and N-cadherin. These results demonstrate that ischemia induces a selective metalloproteinase-dependent cleavage of E-cadherin and decrease in N-cadherin that are associated with a disruption of junctional contacts.

Retention of fetuin-A in renal tubular lumen protects the kidney from nephrocalcinosis in rats

2013 ◽  
Vol 304 (6) ◽  
pp. F751-F760 ◽  
Author(s):  
Isao Matsui ◽  
Takayuki Hamano ◽  
Satoshi Mikami ◽  
Kazunori Inoue ◽  
Akihiro Shimomura ◽  
...  
Keyword(s):  
Rat Kidney ◽  
Proximal Tubules ◽  
Fetuin A ◽  
Receptor Associated Protein ◽  
Tubular Lumen ◽  
Proximal Tubular ◽  
Normal Rat ◽  
Natural Inhibitor ◽  
Renal Tubular

The serum glycoprotein fetuin-A is an important inhibitor of extraosseous calcification. The importance of fetuin-A has been confirmed in fetuin-A null mice, which develop widespread extraosseous calcification including the kidney. However, the mechanism how fetuin-A protects kidneys from nephrocalcinosis remains uncertain. Here, we demonstrate that intratubular fetuin-A plays a role in the prevention of nephrocalcinosis in the proximal tubules. Although normal rat kidney did not express mRNA for fetuin-A, we found punctate immunohistochemical staining of fetuin-A mainly in the S1 segment of the proximal tubules. The staining pattern suggested that fetuin-A passed through the slit diaphragm, traveled in the proximal tubular lumen, and was introduced into proximal tubular cells by megalin-mediated endocytosis. To test this hypothesis, we inhibited the function of megalin by intravenous injection of histidine-tagged soluble receptor-associated protein (His-sRAP), a megalin inhibitor. His-sRAP injection diminished fetuin-A staining in the proximal tubules and led to urinary excretion of fetuin-A. We further analyzed the role of fetuin-A in nephrocalcinosis. Continuous injection of parathyroid hormone (PTH) 1–34 induced nephrocalcinosis mainly in the proximal tubules in rats. His-sRAP retained fetuin-A in renal tubular lumen and thereby protected the kidneys of PTH-treated rats from calcification. Our findings suggest that tubular luminal fetuin-A works as a natural inhibitor against calcification in the proximal tubules under PTH-loaded condition.

Cytoplasmic hybrids, by fusing fish erythrophores and normal rat kidney cells

1991 ◽  
Vol 49 ◽  
pp. 266-267
Author(s):  
K.R. Porter ◽  
K.L. Anderson
Keyword(s):  
Rat Kidney ◽  
Structural Features ◽  
Cell Type ◽  
Pigment Granules ◽  
Normal Rat ◽  
Cytoplasmic Hybrids ◽  
Pigment Aggregation ◽  
General Architecture

When cultured together in the presence of PEG, these cells fuse (M1,M3) and survive in vitro for several days. This offers an opportunity to explore the capacity of one cell type (highly organized structurally) to impose it's structural features on a relatively unorganized cell type (NRK). Also, with two cells differing in several respects, one can ask questions regarding a role of the cell center in the control of pigment aggregation and dispersion, as well as the capacity of one cell type to assemble pigment granules in the cytplasm of another.First, in observations on general architecture .the hybrids have numerous microtubules (M3), but not the organized array of thousands observed in the erythrophores (M2). Furthermore, the microtubules in the hybrid are randomly oriented essentially as they are in the NRK cell (M4). There is a tendency observed in the hybrids for the pigment granules to concentrate among the microtubules and the cistemae of the ER (M3). Thus far, however, we have not succeeded consistently with epinephrine to induce aggregation, or with caffeine, dispersion.

scholarly journals Apical-basal polarity regulators are essential for slit diaphragm assembly and endocytosis in Drosophila nephrocytes

2021 ◽  
Author(s):  
Stefanie Heiden ◽  
Rebecca Siwek ◽  
Marie-Luise Lotz ◽  
Sarah Borkowsky ◽  
Rita Schröter ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Protein Complexes ◽  
Slit Diaphragm ◽  
Cell Cortex ◽  
Proximal Tubular Cells ◽  
Tubular Cells ◽  
Filtration Barrier ◽  
Apical Polarity ◽  
Proximal Tubular

AbstractApical-basal polarity is a key feature of most epithelial cells and it is regulated by highly conserved protein complexes. In mammalian podocytes, which emerge from columnar epithelial cells, this polarity is preserved and the tight junctions are converted to the slit diaphragms, establishing the filtration barrier. In Drosophila, nephrocytes show several structural and functional similarities with mammalian podocytes and proximal tubular cells. However, in contrast to podocytes, little is known about the role of apical-basal polarity regulators in these cells. In this study, we used expansion microscopy and found the apical polarity determinants of the PAR/aPKC and Crb-complexes to be predominantly targeted to the cell cortex in proximity to the nephrocyte diaphragm, whereas basolateral regulators also accumulate intracellularly. Knockdown of PAR-complex proteins results in severe endocytosis and nephrocyte diaphragm defects, which is due to impaired aPKC recruitment to the plasma membrane. Similar, downregulation of most basolateral polarity regulators disrupts Nephrin localization but had surprisingly divergent effects on endocytosis. Our findings suggest that morphology and slit diaphragm assembly/maintenance of nephrocytes is regulated by classical apical-basal polarity regulators, which have distinct functions in endocytosis.

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