Glomerular podocytes in cultured rat kidney slices

Summary The ultrastructure of rat glomerular epithelial cells (podocytes) in kidney slices in vitro was examined using qualitative and quantitative electron microscopy. The kidney slices were cultured in Medium 199 with Hanks' salts in a 5% CO₂/95% O₂ environment for up to 14 days. Few changes in podocyte ultrastructure occurred in the first 12 h of culture, but by 24 h cell bodies were rounded, microvilli were present on all podocyte surfaces, and some foot processes had been replaced by flattened expanses of cytoplasm. These changes were more pronounced by 3 days, when some podocytes had developed pseudopodal extensions and appeared to be migrating from glomeruli onto the slice surface. Podocytes could still be identified after 8, 10 and 14 days of culture, although relatively few glomeruli remained at 14 days. Morphometric methods were used to analyse podocyte shape, volume and surface area during the first 4 days of culture. The most significant change involved loss of foot processes: the number of filtration slits per 100 m of basement membrane decreased from 211.8 ± 15.0 (mean ± SD) at the commencement of culture, to 55.3 ± 22.6 after 2 days (P < 0.001). These data provide baseline information for in vitro studies on the effects of nephrotoxins on podocytes.     

A scanning electron-microscopic study of the peripolar cell of the rat renal glomerulus

Summary The interior of Bowman's capsules of rat kidneys has been examined by scanning electron microscopy, and a distinctive population of cells around the exposed vascular poles of glomerular tufts were identified. The cells were situated in the annular groove at the root of the glomerulus, between the parietal epithelial cells and the podocytes. These peripolar cells were dendritic cells with long processes embracing the glomerular arterioles. Up to three peripolar cells were present at each vascular pole and they were mainly distributed in the glomeruli of the outer third of the renal cortex. This first detailed study of the surface morphology of the glomerular peripolar cell supports the suggestion that changes in the diameter of the polar region of the glomerular tuft may cause variations in stretching of the cuff of peripolar cells, and hence modulation of their secretory activity.     

Defective regulation of apical membrane chloride transport and exocytosis in cystic fibrosis

A biochemical link is proposed between recent observations on defective regulation of Cl^– transport in CF respiratory epithelial cells and studies showing altered biological activity of calmodulin in exocrine glands from CF patients. A consensus is emerging that defective -adrenergic secretory responsiveness in CF cells is caused by a defect in a regulator protein at a site distal to cyclic AMP formation. Our results indicate that this protein might be a specific calmodulin acceptor protein which modifies the activity of calmodulin in epithelial cells. Alteration in Ca²⁺/calmodulin dependent regulation of Cl^– transport and protein secretion could explain (i) alterations in Ca²⁺ homeostasis seen in CF, (ii) defective -adrenergic responses of CF cells, and (iii) the observed inability of cyclic AMP (acting via its specific protein kinase, A-kinase) to open apical membrane Cl^– channels in CF epithelial cells. Most of the physiological abnormalities of CF including elevated sweat electrolytes and hyperviscous mucus can be explained on this basis.Abbreviations -adrenergic agonist acting at its receptor cAMP cyclic AMP - PDE phosphodiesterase - CaM calmodulin - Pase phosphatase     

Distribution of histamine in the rat kidney during pregnancy and development

Summary An antiserum against conjugated histamine and two oligonucleotide probes that detect the mRNA encoding L-histidine decarboxylase (HDC) involved in histamine synthesis were used to study the appearance of histamine and its location in the kidneys of fetal, newborn and young postnatal rats and in the kidneys of pregnant rats. On embryonic days 16 and 18 (E16 and E18), some HA-immunoreactive (HA-ir) cells were found within the largest S-shaped bodies. Histamine was found to appear rapidly between the 18th and 20th embryonic days in the convoluted tubules of the kidneys. On postnatal day 0 (P0), the distal convoluted tubules and collecting ducts exhibited bright fluorescence, the intensity of which decreased quickly so that it was faint on day P4 and absent at later stages. In kidneys of pregnant rats HA-ir was found in the epithelium of both the Bowman's capsule, collecting ducts and in a few cells within the tubules. Nonuniform HA-ir was also detected within glomeruli. No evidence for the presence of L-histidine decarboxylase mRNA in kidneys of fetuses or pregnant rats was seen. It is concluded that distinct structures in the developing rat kidney contain histamine during a period around birth from day E20 to day P4. In the pregnant rat, the epithelium that is in direct contact with the urine flow is immunoreactive for histamine from day 16 to 20 of pregnancy. The results suggest that histamine is not synthesized locally in the kidneys but rather originates from other tissues.     

Contractile proteins in podocytes: immunocytochemical localization of actin and alpha-actinin in normal and nephrotic rat kidneys

Actin and alpha-actinin immunoreactive sites have been localized at the electron microscope level by the protein A-gold immunocytochemical technique in podocytes of normal and nephrotic rat renal tissues. In normal renal glomeruli, fibrillar networks located in the core of foot processes or bundles of micro filaments interconnecting them were found to be labelled for these two cytoskeletal proteins. On the other hand, in nephrotic renal glomeruli, concomitant with the loss of podocytic foot processes a reorganization of the podocytic cytoskeleton and a concentration of some of its elements into thick uniform bands was observed. Actin and alpha-actinin were revealed in these bands. Control experiments confirmed the specificity of the labelling obtained. Our results suggest that normal podocytes contain an actin-based contractile system that might contribute to the maintenance of the particular cell shape of these cells and that the rearrangement of the podocytic cyto-skeleton occurring in the nephrotic syndrome might account for the changes in the foot processes and contribute to the alteration in glomerular function. This work was supported by grants from the Medical Research Council of Canada     

Cell junctions in the renal tubule of a fresh-water teleost,Salmo gairdneri Rich.

Summary Cell junctions in the renal tubule of the fresh-water rainbow trout were studied with thin-section and freeze-fracture techniques. Gap junctions were restricted to the proximal tubule, which is consistent with other vertebrate classes. Segments I and II of the proximal tubule and the collecting tubule/collecting duct system exhibited a well-developed zonula occludens with anastomosing strands. The distal segment showed a narrow zonula occludens composed of few parallel strands. The structure of the occluding junctions along the renal tubule of this teleost displays several similarities with the pattern of the zonulae occludentes in the amphibian and the mammalian nephron. From these observations, in conjunction with available data from other vertebrate classes, it can be concluded that in the proximal tubule the development of a deep and complex zonula occludens is a general feature of cold-blooded vertebrates.     

A new life table of leaves ofPhaseolus vulgris L. in relation to their position within the canopy and plant density

In order to demonstrate in detail the relationship between the longevity and productivity of leaves within a canopy, a new life table approach, the ‘bioeconomic life table’, was applied to the leaves of kidney bean plants (Phaseolus vulgaris L.) in relation to planting density and their position within the canopy. The net photosynthetic rate for upper leaves under full daylight tended to decline gradually due to leaf senescence from about 20 days after leaf emergence, and for the lower leaves the decrease was very rapid due to both shading and senescence about 10 days after emergence. Analysis of the survivorship curves and daily surplus production of leaves suggested that the lower and middle leaves, especially the latter, survived without surplus production of dry matter after they had reached mean longevity, and while the upper leaves at high density had a much shorter mean longevity, they had very large values of daily surplus production throughout the survival period. For the total foliage, the summed value of accumulated surplus production during the survival period was about five times as large as the summed value of the dry weight of the dead leaves, regardless of planting density. The daily rate of canopy leaf respiration was almost proportional to that of canopy gross photosynthesis for the various leaf area indices of the canopy, so that there was no optimum leaf area index that maximized canopy daily surplus production.     

The conversion of injected glucose into renal glycogen and mucopolysaccharides

Summary Tritiated glucose has been injected into rabbits in various states of hydration. The renal papilla of all animals showed an uptake of the label, converted into glycogen, and into mucopolysaccharides, in a manner dependent on the water balance of the animal.In papillae of control animals, the glycogen of the collecting duct epithelial cells and the mucopolysaccharides of the interstitium were labelled.In papillae of animals in an aqueous diuresis, the collecting duct glycogen was lightly labelled and there was no label over the interstitium.Antidiuretic hormone caused a diversion of label from the collecting ducts into interstitial mucopolysaccharides.The significance of these findings, with respect to renal concentrating ability, is discussed.The author wishes to thank Dr. M. K. S. Hathorn for help with the statistical analysis. Mr. K. Gamblin and Mr. P. L. Hyam gave valuable technical assistance. This research formed a part of the work approved for the degree of Ph. D. (London).     

Zur Feinstruktur der Maxillarnephridien von Scutigerella immaculata Newport (Symphyla,Myriapoda)

Zusammenfassung Die Feinstruktur der Maxillarnephridien von Scutigerella immaculata Newport mit ihren drei Abschnitten Sacculus, Tubulus und Ausführgang wurde untersucht. Die Zellen des Sacculus sind typische Podocyten, an denen eine Ultrafiltration ablaufen kann. Möglicherweise wird die Filtration durch einen den Sacculus umgebenden Muskel unterstützt. Die Zellen des Tubulus zeigen basale Einfaltungen und im proximalen Teil auch Mikrovilli. Sowohl im Tubulus als auch im Ausführgang, dessen Zellen ebenfalls basale Einfaltungen aufweisen, werden Reabsorptionsprozesse vermutet.

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The fine structure of the maxillary kidney of the garden centipede, Scutigerella immaculata Newport (Symphyla, Myriapoda)

Summary The fine structure of the maxillary kidney of Scutigerella immaculata Newport (Symphyla) has been investigated. It may be compared with segmental organs of other Arthropoda having an end-sac which forms a primary urine by ultrafiltration. The filtration may be supported by a muscle surrounding the end-sac. The tubular part of the nephridium and the efferent duct show structures which may be involved in reabsorption.