B. Kaissling

Ecto-5'-nucleotidase: localization in rat kidney by light microscopic histochemical and immunohistochemical methods.

We demonstrated the distribution pattern of ecto-5-nucleotidase (5-Nu) in rat kidney by enzymatic activity (lead salt precipitation) and by immunohistochemistry with a polyclonal antibody raised in rabbits. Enzyme activity was found in the brush border of the proximal tubule, highest in the P1 segments with decreasing intensity in the P2 segments and weakest in P3 segments in the medullary rays of the cortex. The P3 segments of the outer stripe showed slightly higher activity. Activity was also apparent in the intercalated cells in the connecting tubule and collecting duct, whereas all other tubular and glomerular structures were negative. Activity in peritubular and perivascular connective tissue was highest in the cortical labyrinth, weak or absent in the medullary rays of the cortex, and entirely absent in the medulla. The distribution of the antigen was fully congruent with that of the enzyme activity. With respect to the role of adenosine in regulation of renal blood flow and glomerular filtration rate, the distribution of 5-Nu in the cortical interstitium may be particularly significant. The possibility of nucleotide cleavage at the brush-border membranes may be important for salvage of nucleotides from the tubular lumen.

Distal tubular segments of the rabbit kidney after adaptation to altered Na- and K-intake

SummaryThe baso-lateral cell-membrane area in kidney tubules appears to be associated with the capacity for electrolyte transport; in the rabbit, it decreases from the distal convoluted tubule (DCT-cells) over the connecting tubule (CNT-cells) to the cortical collecting duct (principal cells).Adaptation to low Na-, high K-intake changes this pattern: CNT-cells at the beginning of the connecting tubule have the highest membrane area, which decreases along the segment, but remains two-fold higher than in controls. Principal cells have a four-fold higher membrane area than in controls. Simultaneous treatment with the antimineralocorticoid canrenoate-K inhibits the structural changes in CNT-cells only in end-portions of the connecting tubule and in principal cells.After prolonged high Na-, low K-intake DCT-cells display a two-fold higher membrane area than controls, while CNT-cells and principal cells are not affected. Simultaneous treatment with DOCA does not affect the DCT-cells but provokes a moderate increase in membrane area in CNT-cells, and a 5.5-fold increase in principal cells.The data provide evidence that DCT-, CNT- and principal cells are functionally different cell types. The baso-lateral cell-membrane area, associated with electrolyte-transport capacity, appears to be influenced in DCT-cells mainly by Na-intake, in CNT-cells mainly by K-intake and in part also by mineralocorticoids, and in principal cells mainly by mineralocorticoids.

Gap junctional coupling between the JGA and the glomerular tuft

SummaryThe juxtaglomerular apparatus (JGA) in the rabbit kidney was examined by transmission electron microscopy and by freeze fracturing. It was found, that the Goormaghtigh cells of the JGA are extensively coupled with the mesangial cells within the glomerular tuft by gap junctions. A broad band of gap junctions starting within the Goormaghtigh cells, traversing the transitional area at the root of the glomerular tuft and continuing along the mesangial cells has been revealed by freeze fracturing. No gap Junctional connections to the macula densa cells have been found. In accordance with data from literature it may be stated that all smooth muscle derived cell groups at the vascular pole of the glomerulus (smooth muscle cells of the vas afferens and efferens, granular cells, Goormaghtigh cells, mesangial cells) are extensively coupled by gap junctions with each other. It is supposed that this cell system may act as a synchronized functional unit.

The transition of the thick ascending limb of Henle's loop into the distal convoluted tubule in the nephron of the rat kidney

SummaryExamination of serial semithin sections of rat kidney cortex and a subsequent electron microscopic study of selected areas revealed that the characteristic epithelium of the cortical part of the thick ascending limb of Henle extends for a varying distance beyond the macula densa. The transition from the relatively thin epithelium of the thick ascending limb at this site to the three -or even four-fold thicker epithelium of the convoluted part of the distal tubule is sharply defined and occurs without the interposition of an intermediate cell type.The position of the macula densa at the end but still clearly within the ascending limb of Henles loop is functionally interpreted to guarantee the separation of the sensor point macula densa from disturbing influences which might arise from the secretory activity of the subsequent tubular portion.

Endothelial cells modulate renin secretion from isolated mouse juxtaglomerular cells.

Utilizing cocultures of mouse renal juxtaglomerular cells with bovine microvascular endothelial cells, we have examined whether endothelial cells exert direct influence on renin secretion from renal juxtaglomerular cells. In the presence of endothelial cells both spontaneous and forskolin (10 microM) or isoproterenol (10 microM) stimulated renin release were markedly attenuated. The stimulatory effect of the calmodulin antagonist calmidazolium (10 microM) on renin secretion was not altered by endothelial cells, whereas the stimulatory effect of ethylisopropylamiloride (50 microM) an inhibitor of sodium-proton exchange was enhanced in the presence of endothelial cells. Indomethacin (10 microM) and NG-monomethyl-l-arginine (NMMA) (1 mM) used to inhibit cyclooxygenase activity and production of endothelium-derived relaxing factor (EDRF) decreased spontaneous renin release in the presence of endothelial cells only, but had no effect on forskolin stimulated renin secretion. Endothelin (1 microM) inhibited cAMP stimulated renin release both in the absence and in the presence of endothelial cells. ATP (10 microM) which acts on both endothelial and juxtaglomerular cells via purinergic P2 receptors inhibited cAMP stimulated renin release only in the absence but not in the presence of endothelial cells. This modulatory effect of endothelial cells was no altered by indomethacin nor by NMMA. Taken together, our findings provide first evidence for a local control function of the endothelium on cAMP stimulated renin secretion from renal juxtaglomerular cells, which could in part be mediated by endothelin.

The vascular organization of the kidney of Psammomys obesus.

SummaryThe vascular organization of the kidney of Psammomys obesus has been studied by injecting silicone rubber into the renal arterial and venous vessels and by standard histological techniques.Whereas the cortical vasculature is not principally different from that of other species, the medullary vessels show some unique features in the Psammomys. In the outer stripe, the vasa efferentia of juxtamedullary glomeruli give rise to primary vascular bundles which, in the transitional region between the outer and inner stripes, fuse to form secondary and, finally, giant vascular bundles.In the inner stripe exist two clearly separated vascular compartments that of the giant bundles and that of the interbundle region. The latter is supplied by arterial vasa recta originating from the upper part of the vascular bundles at the entrance to the inner stripe. In the lower portion, the separation of the two compartments is enhanced by vessel-free rims around the bundles (the rims contain descending, limbs of long loops only) and by protrusions of the renal pelvis.The inner zone is supplied exclusively by the vasa recta descending throughout the inner stripe within the vascular bundles. They splay out of the bundles at the transitions from outer to inner medulla, and descend individually as straight unbranched vessels. Many of them do not split up into capillaries before they reach the tip of the papilla.The venous drainage of the inner zone is ensured by venous vasa recta ascending individually up to the border between the inner zone and the inner stripe. They all enter the giant vascular bundles within which they traverse the inner stripe. The venous vessels draining the interbundle, region of the inner stripe do not join the bundles but ascend directly to the outer stripe. Thus, the circulations of the, outer and inner medullary zones are totally separated from each other.In the outer stripe venous vasa recta from the bundles and from the interbundle areas are mixed together. Most of them ascend high into the cortex within the medullary rays in close apposition to tubules, and empty into interlobular veins.

Ultrastructural organization of the transition from the distal nephron to the collecting duct in the desert rodent Psammomys obesus.

SummaryThe transition from the nephron to the collecting duct is formed by three tubular segments (convoluted part of the distal tubule, connecting tubule, cortical collecting duct), which in the desert rodent, Psammomys obesus, transform gradually from one segment to the next, due to intermingling of their different cell types.The convoluted part of the distal tubule (DTC) starts abruptly, shortly beyond the macula densa and initially is homogeneously composed of characteristic DTC-cells. Subsequently, the DTC-cells intermingle with intercalated cells. The first appearance of the connecting-tubule cell, which gradually replaces the DTC-cell, is regarded as the beginning of the connecting tubule. The major portion of the connecting tubule is lined by connecting-tubule cells and intercalated cells. The first appearance of the principal cell between them defines the beginning of the cortical collecting duct, which in the medullary ray is lined by principal and intercalated cells only.Each cell type is described in detail and discussed in relation to the assumed function of the tubular segments.Interspecies differences in the cellular composition of the transitional zone from the nephron to the collecting duct are discussed in relation to the different organization of the collecting duct system.

Three-dimensional shape of a Goormaghtigh cell and its contact with a granular cell in the rabbit kidney

SummaryGoormaghtigh cells of the JGA are characterized by an extensive cellular ramification. In order to elucidate the shape and arrangement of the cell processes a three-dimensional model of a Goormaghtigh cell and of an adjacent granular cell has been constructed based on electron micrographs of a series of ultrathin sections.The model shows that a Goormaghtigh cell has the shape of a flatly pressed cylinder with both ends splitting up into a bunch of parallel processes. The processes maintain a close neighboring position and do not intermingle with processes of other Goormaghtigh cells. This feature is most puzzling when considering that Goormaghtigh cells and their processes are extensively connected by gap junctions. Even processes belonging to the same cell are electrically coupled with each other through gap junctions.The granular cells are clearly different in shape from Goormaghtigh cells. In granular cells bunches of processes are lacking. Granular cells obviously ramify into a few, large processes.The present findings are consistent with the assumption of a functionally central position of Goormaghtigh cells within the feedback mechanism of the JGA.

Anemia Induces 5’-Nucleotidase in Fibroblasts of Cortical Labyrinth of Rat Kidney

We recently observed a strong increase of 5-nucleotidase in renal fibroblasts of rats that were anemic due to an immunity against erythropoietin. In order to test if the change of 5-nucleotidase was related with anemia, we studied the distribution of the enzyme in irradiated rats treated with phenylhydrazine. The hematocrit of these rats decreased to 15% within 4 days and erythropoietin levels were more than 200 times over controls. After 7 days a histochemical study showed that the enzymatic activity and the immunoreactivity for 5-nucleotidase was markedly enhanced in the fibroblasts of the cortical labyrinth. There was no modification of 5-nucleotidase in other cell types of the kidney. The 5-nucleotidase activity of renal fibroblasts in cell culture increased by 72% upon addition of 160 microM 5-AMP to the culture medium for 8 days. We propose that anemia provokes an energy deficit in some structure in the cortical labyrinth. This might increase the concentration of 5-AMP which would induce 5-nucleotidase. An interesting consequence of these events would be an increased production of adenosine in the direct vicinity of some of its putative targets, the glomerular arterioles and the erythropoietin-producing cells.

Morphologische Merkmale transportierender Epithelien

Transportierende Epithelien sind geschtossene Zellverb/inde, die basal an ein Interstitium (ira weitesten Sinn), apikal (luminal) an eine innere oder fiul3ere K6rperoberflfiche grenzen. Sie trennen unterschiedlich zusammengesetzte Kompartimente voneinander. Die Transportleistungen des Epithels sind an der Schaffung und Aufrechterhaltung der Unterschiede direkt beteiligt. Ein transportierendes Epithel hat somit zwei Funktionen, die in seinem Aufbau gewfihrleistet sind. Das Epithel bildet zum einen eine Barriere, die den Ausgleich der Unterschiede hindert, zum anderen transportiert es bestimmte Substanzen von einer Seite des Epithels auf die andere; im einzelnen heil3t dies : es hindert entweder deren Durchtritt nicht (Diffusion), erleichtert ihn auf passive Art (trggervermittelte Diffusion) oder transportiert sie aktiv, somit unter Energieverbrauch. Die Transportfunktionen eines Epithels sind spezifisch. Sind die Transporte vorwiegend nach basal (d.h. ins Interstitium) gerichtet, so spricht man von resorbierenden, im umgekehrten Fall von sezernierenden Epithelien. Die meisten transportierenden Epithelien sind einschichtig (Darmepithel, Nephronepithel), doch kommen auch mehrschichtige sehr aktiv transportierende Epithelien vor (Froschhaut). Die Zusammensetzung eines transportierenden Epithels kann homogen sein, d.h. es besteht nut aus einem Zelltyp; heterogene Epithelien bestehen aus zwei oder mehreren Zelltypen. Wir werden unsere Betrachtung auf Epithelien beschr/inken, die aus einer Schicht gleichartiger Zellen bestehen. Dies vereinfacht die Darstellung, ohne dabei strukturelle Fragen yon prinzipieller Bedeutung auslassen zu mfissen. Wir werden weiterhin in dieser Betrachtung nur die strukturellen Fragen des Trans-