R. Taugner

Myoendothelial contacts in glomerular arterioles and in renal interlobular arteries of rat, mouse and Tupaia belangeri

SummaryCell contacts between elements of the tunica media and the intima in the afferent and efferent glomerular arteriole and in the interlobular artery were studied and evaluated semiquantitatively in thin sections of rat and mouse kidney.In the afferent arterioles, including their juxtaglomerular portion, contacts were seen between endothelial and smooth muscle cells, and between endothelial and granulated (renin producing) cells. The form of these musculoendothelial contacts varied from simple appositions of perikarya and cell processes to extensive club-shaped indentations of endothelial cells into media cells (common) or media cells into endothelial cells (rare). Most of these cell contacts seem to contain myoendothelial gap junctions. Fewer, mostly club-shaped myoendothelial contacts were found in the interlobular arteries of rats and mice than in their afferent arterioles. Simple membrane appositions predominated among the numerous myoendothelial contacts of efferent arterioles. Similar results (without quantitative analysis) were obtained in the kidney of Tupaia belangeri. The myoendothelial contacts may allow the detection and propagation of mechanical (autoregulatory) and humoral stimuli.

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 Intrarenal Renin-Angiotensin-System An Immunocytochemical Study on the Localization of Renin, Angiotensinogen, Converting Enzyme and the Angiotensins in the Kidney of Mouse and Rat*

SummaryThe localization of renin, converting enzyme (CE) and angiotensin II (ANG II) in the kidneys of rats and mice was investigated with immunocytochemical methods. According to the presence and specific intrarenal localization of these components of the renin-angiotensin-system (RAS) our results suggest that in addition to the well known systemic effects of the RAS, there are interactions of its components inside the kidney. These interactions may lead to the generation of an extra portion of ANG II in the renal blood stream with its target cells determined by the localization of CE at the luminal side of well defined endothelial areas. These intrarenal-intravasal reactions may or may not reinforce the action of “systemic” ANG II, generated prerenally. In addition, the existence of true intrarenal-interstitial interactions, with the different components and actions of this intrarenal RAS restricted entirely to the kidney is suggested by our results, particularly the demonstration of ANG II within epitheloid cells and the dissociation of systemic renin and ANG II from their local concentrations in renal hypertensive rats.ZusammenfassungDie intrarenale Verteilung von Renin, Converting enzyme (CE) und Angiotensin II (ANG II) wurde mit immunzytochemischen Methoden an Ratten und Mäusen untersucht. Die hier aufgezeigten spezifischen Verteilungsmuster dieser Komponenten des Renin-Angiotensin-Systems (RAS) legen die Annahme nahe, daß es neben den bekannten systemischen, durch ANG II vermittelten Effekten des RAS auch lokale Interaktionen von RAS-Bestandteilen innerhalb der Niere gibt. — Eine erste Folge dieser Interaktionen dürfte die intrarenale Generation einer zusätzlichen Portion von ANG II im Nierenblutstrom sein, deren Zielgebiet durch die spezifische Lokalisation von CE in bestimmten Endothelbereichen der Nierenstrombahn bestimmt wird. Solche intrarenal-intravasalen Reaktionen können für sich wirksam werden, aber auch den Effekt von „systemisch“, d.h. prärenal generiertem ANG II verstärken. — Unsere Ergebnisse sprechen weiter dafür, daß es neben diesen intrarenal-intravasalen auch echte intrarenal-interstitielle Interaktionen der RAS-Komponenten gibt, deren Wirkung sich über das im Interstitium der Nierenrinde generierte ANG II allein auf die Niere beschränkt. Für das Vorhandensein eines solchen lokal-intrarenalen RAS spricht vor allem der Nachweis von ANG II in den epitheloiden Zellen des JGA und die Dissoziation des systemischen — an der Plasmakonzentration abzulesenden — Renin und ANG II von deren lokal-intrarenalen Konzentrationen bei renal hypertensiven Ratten.

Ultrastructural changes associated with renin secretion from the juxtaglomerular apparatus of mice.

SummaryThin sections and freeze-fracture replicas were used to investigate the ultrastructural changes associated with renin secretion from the juxtaglomerular part of the afferent arteriole of male mice. Adrenalectomized animals in which renin secretion was stimulated by furosemide application and bleeding were also studied. Exocytosis of mature electron-dense granules was found in all experimental groups. Before extrusion, the region of granule facing the cell membrane changed, with vesicular and/or stacked membrane-like profiles and a small local protrusion of the granule membrane appearance of. Concomitantly, punctuate sites of fusion between the cell and granule membranes were observed. Later, unaltered amorphous, and altered membrane-like granule content was released from omega-shaped cavities into the extracellular space. In stimulated animals the alteration and extrusion of several closely apposed granules was reminiscent of compound exocytosis. Coated pits were frequently seen, suggesting specific retrieval of the former granule membrane. The collapsing silhouette of a depleted granule very rarely took the form of a saccule whose narrow membrane-bounded neck was continuous with the extracellular space.Observed were two additional events by which active and inactive renin may be released. Small electron-lucent vacuoles of undetermined origin fused with the cell membrane and, in stimulated kidneys, some epithelioid cell processes disintegrated. However, the interpretation of the related ultrastructural phenomena was uncertain.

Coexistence of renin and cathepsin B in epithelioid cell secretory granules

SummaryMature juxtaglomerular epithelioid cell secretory granules of the rat exhibit both renin- and cathepsin B-like immunoreactivity. On the basis of the coexistence with renin at a pH which, according to previous experiments, is probably in the range of that in lysosomes, cathepsin B is suggested to be involved in the activation of renin prior to secretion.

Converting-enzyme in the choroid plexus, brain, and kidney: Immunocytochemical and biochemical studies in rats

In rats, immunoreactivity was demonstrated in the brush border of the choroid plexus, in the wall of blood vessels in the brain, and in the brush border of the proximal tubules of the kidney, using the peroxidase-antiperoxidase technique (PAP) and an anti-pulmonary converting-enzyme antibody. These findings correlate with biochemical data of converting-enzyme activity in the choroid plexus and in other tissues. Possible functions of the enzyme in relation to its localization are discussed.

Renin immunocytochemistry of the differentiating juxtaglomerular apparatus.

SummaryThe differentiation of the juxtaglomerular apparatus in fetuses and newborn mice was investigated by renin immunocytochemistry and electron microscopy.Three to four days before delivery and prior to other organs renin was found in the fetal kidney. At this early time immunoreactivity was preferentially located in cells of the media of interlobular arteries.In newborn mice the formation of new nephrons and maturation of their glomeruli was accompanied by a shift in renin localization from the interlobular arteries to the afferent arterioles. At the same time, kidney renin content and concentration increased rapidly.Synchronously with renin immunoreactivity, during the capillary loop stage of glomerular development, granulated epitheloid cells became visible in the afferent arteriole.

Are the renin-containing granules of juxtaglomerular epithelioid cells modified lysosomes?

SummaryMature secretory granules of epithelioid cells — the so-called renin granules — exhibit certain properties, which in this particular combination are expressed only by lysosomes: Renin granules have autophagic capabilities; they react to the application of lipidosis-inducing, lysosomotropic substances by the gradual accumulation of polar lipids; all secretory granules of epithelioid cells contain acid phosphatase until maturity; and exogenous tracers reach renin granules without labeling the Golgi complex. Several functional implications can therefore be considered. Hydrolytic enzymes, constitutive elements of the granule matrix, might either cleave inactive prorenin to yield active renin within the granules or, by unspecific hydrolysis of renin, participate in the regulation of the overall quantity of secretory product. Autophagic phenomena, the involvement of renin granules in the traffic of exogenous tracers, and the build-up of polar lipids following experimental interference with lipid catabolism indicate a large turnover of membrane material in renin granules. They also suggest that cytoplasmic and extracellular fluid gains access to the granule content and may thus be involved there in the regulation of biochemical reactions by changing the intragranular milieu or via signal molecules.In addition to the lysosome-like properties of epithelioid cell secretory granules, the secretory product, renin, as a carboxyl protease, is structurally related to other acidic proteases. In the case of cathepsin D, even functional similarities exist.

Coexistence of renin and angiotensin II in epitheloid cell secretory granules of rat kidney

SummaryThe distribution of renin and angiotensin II (ANG II) in juxtaglomerular epitheloid cells of control and adrenalectomized rats was studied, using specific antisera and the protein A-gold technique in Lowicryl- and glycol methacrylate-embedded tissue.The matrix of virtually all mature secretory granules of epitheloid cells contains not only renin, but also ANG II. On adrenalectomy, the concentration of both renin and ANG II in the granule internum increases markedly, as indicated by the density of the immunolabel.Given the coexistence of renin and ANG II in the granule matrix, it is quite probable that, with each secretory event, a certain amount of ANG II is released together with renin. Further experiments will have to show if this amount of ANG II cosecreted with renin is sufficient to elicit immediate local intrarenal actions.ANG I, as well as angiotensinogen and converting enzyme, were not found in epitheloid cells. It is therefore inferred that ANG II is not generated intracellularly, but within the extracellular space and subsequently taken up by pinocytosis and incorporated into the secretory granules of epitheloid cells.

Glial cells in the pineal gland of mice and rats

SummaryAntigenic markers characteristic of astrocytes and their differentiative states (i.e., glial fibrillary acidic protein (GFAP), vimentin, and M1 and C1 antigens) were investigated in the pineal gland of mouse and rat using double immunolabeling techniques. In both species the socalled interstitial cells as characterized by TEM were shown to be astrocytes, since they expressed vimentin, but neither fibronectin (a marker for fibroblasts and endothelial cells) nor the neuron-specific L1 antigen or tetanus toxin receptors. Subpopulations of vimentin-positive pineal astrocytes were also GFAP- and C1- antigen-positive. M1- antigenpositive cells were not detected.It is concluded that a considerable proportion of interstitial cells in the pineal gland of rat and mouse are immature astrocytes which, in contrast to other parts of the central nervous system, persist into adulthood.