PubMed Health⌕ Search

Biomedical subjects

W Pfaller

Publications and source records attributed to W Pfaller.

52 records · Page 3Linked to original sources
PubMed1976

A critical reevaluation of the structure of the rat uriniferous tubule as revealed by scanning electron microscopy.

The fine structure of luminal surface of clearly identified portions of uriniferous tubules has been studied by scanning electron microscopy to elucidate some controversies concerning the topography of certain surface formations. The results show a characteristic pattern of the luminal surface in the region of Henle's loop, which was assumed by previous authors, to belong to the collecting tubule. Furthermore it is demonstrated that no cilia are present within the terminal portion of the collecting tubules.

Animals↗
PubMed1976

A comparison of the ultrastructure of spray-frozen and freeze-etched or freeze-dried bull and boar spermatozoa with that after chemical fixation.

The ultrastructure of bull and boar spermatozoa was investigated following different cryopreparation methods and chemical fixation. Spray-freezing was used for cryofixation in both freeze-etching and freeze-drying studies. Freeze-etching of boar spermatozoa revealed that the arrangement of the postnuclear striations differed from that in the bull. Freeze-drying gave excellent results for structural preservation, which were equal to those of chemical fixation. Some structural details not visible in chemically fixed cells were detected in freeze-dried and vacuum-embedded bull and boar spermatozoa, e.g. the arrangement of the lamellar nuclear contents, known from freeze-fractures, and a fine lamellar structure of the acrosomal contents. Cryofixation by spray-freezing combined with freeze-drying makes any contact of the cells with fixatives, buffer solutions and dehydration media unnecessary, and potentially provides all the advantages of ultrathin sectioning required for histochemical studies.

Acrosome↗
PubMed1976

Molecular specificity of tubular amino acid reabsorption.

The specificity of tubular reabsorption of L-arginine and L-methionine was investigated by continuous microperfusion of single proximal convolutions of the rat kidney. The following observations were made: 1) L-arginine reabsorption form the tubular lumen is saturable and can be inhibited by cycloleucine and some L-arginine derivatives with the following structure: -OOC -- CH (N+H3) -- (CH2)x -- N+H (R1) -- R2 The optimal value of x is 3 to 4. The methylene group adjacent to the nitrogen can be replaced by an oxygen atom. The radicals R1 and R2 have to permit ionization of the vicinal nitrogen. L-cysteine, L-homoserine, and diaminodicarboxylic acids do not inhibit L-arginine reabsorption. 2) L-methionine reabsorption is mainly a saturable process (Vmax = 2.5 x 10-(11) mol/cm/sec; Km = 6.1 mM). Passive diffusion does not play an important role (permeability coefficient = 2.45 x 10(-7) cm2/sec. 3) D-methionine also uses this saturable system for reabsorption. However, the affinity in this case is much smaller (Km = 23 mM). 4) L-phenylalanine, L-iso-leucine, L-ethionine, and cycloleucine seem to share this mechanism with L-methionine. In addition, the autoradiographic method was employed to determine on which side of the tubular cell competition of L-arginine and L-lysine for reabsorption occurs. Good evidence was obtained that the specific receptor for these two amino acids is located at the luminal membrane.

Animals↗
PubMedDate not supplied

Lipid peroxidation--an initial event in experimental acute renal failure.

A method was developed to monitor the occurrence of lipid peroxidation (LPO) during ischemia and Na-maleate-induced acute renal failure (ARF) on male rats in vivo by measuring malondialdehyde (MDA) levels in arterial and renal venous blood and in urine. No signs of LPO could be detected under control conditions. In ischemic ARF produced by 45 min of renal artery clamping a steep increase of MDA was found in the renal venous effluent immediately after starting reperfusion. This effect was nearly abolished after 5 min of blood reflow while glomerular filtration remained at 5% of control value during a 90-min postischemic observation period. Intoxication with Na-maleate leads to enhanced LPO in combination with an impaired renal function 2 h after administration. These findings would well explain cellular damage and some aspects of renal dysfunction associated with the initiation phase of ARF.

Acute Kidney Injury↗
PubMedDate not supplied

Quantitative morphologic changes in nephron structures and urinary enzyme activity pattern in sodium-maleate-induced renal injury.

The morphologic changes in sodium-maleate-induced acute renal injury in the rat were quantified by a stereologic analysis. The major changes were confined to an increase in endocytic vacuoles and a decrease in mitochondrial inner membrane surface area. These results were found to be linked to significantly increased urinary activities of the cytosolic of the cytosolic enzymes fructose-1,6-bisphosphatase (FBP) and lactate dehydrogenase, the lysosomal enzyme N-acetyl-beta-glucosaminidase (NAG) and the NAD-dependent mitochondrial isocitrate dehydrogenase (ICDH). The highest increase was found for NAG, followed by FBP and ICDH.

Animals↗
PubMedDate not supplied

Carbonic anhydrase activity in Madin Darby canine kidney cells. Evidence for intercalated cell properties.

Madin Darby canine kidney (MDCK) renal epithelial cell cultures have been investigated with respect to their potency to express carbonic anhydrase activity using histochemical methods. Acetazolamide inhibitable carbonic anhydrase activity could be detected in the cytoplasmic compartment as well as in the apical membrane of cells when grown on solid culture supports. Cells forming domes in MDCK monolayers exhibit the highest histochemically detectable enzyme activity. The attempt to subculture clonal cell lines from MDCK monolayer cultures resulted in the establishment of 5 clones, slightly different with respect to size and shape of cells and their potency to form domes. Scanning electron microscopy ensured the identification of one clone (1A4), which distinctly differed from the others with respect to the apical membrane architecture. Co-localization of peanut agglutinin and carbonic anhydrase activity at the plasma membrane always revealed a combined occurrence of enzyme reactivity and lectin binding in the apical membrane domain. Both, lectin binding and carbonic anhydrase activity were distinctly more intense in plasma membrane regions equipped with microvilli. From the results it is concluded that MDCK cells in tissue culture retained properties of intercalated cells of the nephron collecting duct segment.

Animals↗
PubMedDate not supplied

Volume-regulatory potassium release from isolated perfused rat kidney.

The present study has been performed to test for cell volume regulatory potassium release from the isolated perfused rat kidney exposed to hypotonic perfusate and for its sensitivity to potassium channel blocker barium and calcium channel blocker verapamil. Replacement of 25 mmol/l NaCl with 50 mmol/l mannitol has little effect on effluent potassium activity, whereas subsequent omission of mannitol from the perfusate leads to a transient increase of effluent potassium activity, reflecting volume regulatory potassium release. Barium (1 mmol/l) leads to a marked transient decrease of effluent potassium activity, pointing to net cellular uptake of potassium. Verapamil (1 mumol/l) leads to a slight decrease of effluent potassium activity. Both barium and verapamil virtually abolish the rapid, transient increase of effluent potassium activity upon exposure to hypotonic perfusates. Thus, the substances either block or markedly retard volume regulatory potassium release. The apparent renal vascular resistance is transiently increased by exposure to hypotonic perfusates and by barium, but is reduced by verapamil. Cell volume regulation of isolated perfused mouse straight proximal tubules is retarded but not abolished by verapamil (0.1 mmol/l). In conclusion, cellular potassium release from rat kidney can be determined by continuous measurement of effluent potassium activity. The volume regulatory potassium release and cell volume regulation are impaired by both barium and verapamil. The persisting cell volume regulation could be due either to slow potassium release and/or some mechanism independent of potassium.

Animals↗
PubMedDate not supplied

Modification of membrane protein expression and protein secretion in LLC-PK1 cultures grown on different carbohydrates.

Membrane glycoproteins and glycolipids play an important role in epithelial organization, transport and function. To study the effects of exogenous carbohydrates on the expression of glycoproteins, cells of the renal epithelial line LLC-PK1 were cultured on different nutritive carbohydrate sources and on uridine, which is, despite striking differences, known to substitute all essential nutritive functions of glucose. LLC-PK1 cultures were long-term adapted to growth in culture medium containing 0.5, 5, 10 and 25 mM glucose, and 5 mM fructose, galactose and uridine, respectively, as the sole carbohydrate source. These growth conditions elicited adaptive changes in the expression of enzyme activities of alkaline phosphatase and gamma-glutamyltranspeptidase, integral membrane glycoproteins exclusively localized in the apical membrane of LLC-PK1 cells. SDS-PAGE of membrane preparations of adapted LLC-PK1 cells revealed a strong induction of several protein bands between 13.5 and 47 kD in fructose-grown cells, while in plasma membranes of cells grown in galactose several protein bands between 62 and 70 kD decreased. Changes in the secretion pattern of proteins into the culture medium were most prominent in uridine-grown cells compared to controls grown on 25 mM glucose.

Alkaline Phosphatase↗
PubMedDate not supplied

Morphological and biochemical changes of LLC-PK1 cells during adaptation to glucose-free culture conditions.

The established renal epithelial cell line LLC-PK1 retained in tissue culture several differentiated properties of renal proximal tubular cells. By adapting LLC-PK1 cells to glucose-free culture conditions, we recently succeeded in isolating a gluconeogenic strain of LLC-PK1 cells capable of growing in the absence of hexoses. In contrast to the parental wild type, the isolated strain expressed fructose-1,6-bisphosphatase activity and was, therefore, designated LLC-PK1-FBPase+. Besides the differences in glucose metabolism, the isolated gluconeogenic substrain differs form the parental wild type with respect to morphological appearance and the expression of apical membrane marker enzymes. LLC-PK1-FBPase+ cells display a drastic accumulation of autophagic vacuoles, disappearance of apical membrane alkaline phosphatase activity, and increased gamma-glutamyltranspeptidase activity. In order to find out whether or not a low alkaline phosphatase activity in combination with the enhanced formation of autophagic vacuoles is related to a change in apical membrane surface, we utilized a combined light and electron microscopic morphometric procedure to determine the absolute amount of organelle volumes and membrane surface areas. This stereologic approach shows that LLC-PK1-FBPase+ cells display a tenfold increase in the volume of autophagic vacuoles and the lysosomal compartment. Analysis of lysosomal enzyme activities, however, revealed no changes as compared to wild-type cells. The apical membrane surface of gluconeogenic cells was found to be increased by 80%. Karyotype analysis revealed that LLC-PK1 wild-type cells were diploid, whereas FBPase+ cells exhibited polyploidy with a high percentage of tetraploid nuclei. Culturing LLC-PK1-FBPase+ cells in the presence of 5 mM glucose does not abolish the morphological and biochemical changes described, indicating the stability of the FBPase+ strain.

Adaptation, Physiological↗
PubMedDate not supplied

Endothelin-3 modulates glomerular filtration rate in the isolated perfused rat kidney.

The present study has been performed to evaluate hemodynamic and tubular effects of various endothelin-3 (ET-3) concentrations on the isolated perfused rat kidney. Using this experimental system we observed a profound reduction of renal perfusate flow at all ET-3 concentrations tested (50, 250 and 500 pmol/l), suggesting that the vasoconstrictive potency of ET-3 in the kidney is comparable to that described for endothelin-1 (ET-1). The effects on glomerular filtration rate (GFR) differed depending on the ET-3 dose applied. While 250 pmol/l ET-3 increased GFR by 30%, 500 pmol/l ET-3 markedly reduced GFR. 50 pmol/l ET-3 did not alter GFR although renal vascular resistance significantly increased. Infusion of 1 mumol/l N-nitro-L-arginine, a specific and potent inhibitor of nitric oxide synthesis in endothelial cells, abolished the GFR elevation induced by 250 pmol/l ET-3. In parallel with the changes of GFR we observed an increase in sodium reabsorption at 250 pmol/l and a decrease of this parameter at 500 pmol/l ET-3. Moreover, an ET-3 concentration (500 pmol/l), which induced a dramatic fall in tubular sodium load, led to an increase of fractional sodium excretion and to a decrease of renal oxygen consumption. We conclude that ET-3 is a potent vasoconstrictor in the isolated perfused rat kidney. Furthermore, it modulates GFR in a differentiated mode, depending on the concentration used. The GFR increase at 250 pmol/l ET-3 seems to be mediated by endothelium-derived nitric oxide. In addition to its glomerular action, ET-3 might also affect tubular sodium transport.

Animals↗