The juxtaglomerular apparatus in the avian kidney

Summary The domestic fowl has two types of glomerulus (mammalian and reptilian type). 30 of each were studied morphometrically in semi thin and PAS-stained sections. The juxtaglomerular apparatus was larger in the mammalian type, but complete in both, containing macula densa, Goormaghtigh (lacis) cells and hilar arterioles. Granular epithelioid cells were occasionally found in the afferent arterioles and within the glomerulus in the mammalian type only.All glomeruli studied had a prominent mesangial cell mass (MCM), which was larger in mammalian type glomeruli. Hilar arterioles often penetrated the mesangial cell mass and regularly ramified within it. There was always extensive direct contact between the Goormaghtigh cell mass and the macula densa on the one side and the MCM on the other. In mammalian type glomeruli, the afferent arterioles were invariably found centrally within the MCM, but in the reptilian type no distinct pattern was found. The close relationship between the MCM and the hilar arterioles, especially in mammalian type glomeruli, suggests that the MCM regulates the glomerular filtration rate.     

Localization of aminopeptidase A (angiotensinase A) in the rat and mouse kidney

Summary Aminopeptidase A (E.C.3.4.11.7; APA) can be demonstrated histochemically in the rat and mouse kidney by light microscopy (simultaneous azo coupling with -Glu-MNA as substrate and high-purity FBB as coupling agent) mainly in the brush borders, glomeruli and portions of the juxtaglomerular apparatus. Sex and species differences are found with regard to enzyme activity and localization. The relation of aminopeptidase A to angiotensinase A was established by inhibition experiments with angiotensin II and III. The following significant differences exist with respect to other aminopeptidases (aminopeptidase M and -glutamyl transferase), which were also demonstrated: APM shows no dependence on calcium ions; APM and -GT are not demonstrable in the glomerulus or juxtaglomerular apparatus.Supported by the Deutsche Forschungsgemeinschaft (SFB 105)     

Aminopeptidase A is angiotensinase A. II. Biochemical studies on aminopeptidase A and M in rat kidney homogenate

Biochemical fluorometric methods were used to investigate aminopeptidase A (APA; E.C.3.4.11.7) in the rat kidney homogenate and glomeruli and to compare it with aminopeptidase M (APM; E.C.3.4.11.2). It is shown that APA is a calcium-ion-dependent enzyme, while APM is not. To clarify the functional importance of APA and APM in the kidney, their activities were measured under the influence of angiotensins. Fluorimetric measurements in renal homogenate (with 2-naphthylamide derivatives as substrates), which represents mixed-enzyme tissue preparations containing a variety of peptidases besides APA and APM, showed a Km of 0.13 mM for APA and competitive inhibition of ANG II (K1 = 0.015 mM), and a Km of 0.24 for APM and competitive inhibition by ANG III (K1 = 0.003 mM). The remaining two angiotensins showed non-competitive inhibition of APA (ANG I, III) and APM (ANG I, II) in this preparation. For comparison purposes, fluorometric measurements were performed in microdissected glomeruli which contain only APA. A Km of 0.23 mM for the APA and a competitive inhibition of APA by ANG I and II were determined. Thus it was possible to show biochemically that APA is equivalent to angiotensinase A and that both APA and APM participate in angiotensin degradation in the kidney. APA initiating the breakdown of ANG I and II, and APM possibly continuing it in sequential fashion.     

Ultrastructural and morphometric aspects of the juxtaglomerular apparatus in the monkey kidney

Summary The authors describe the ultrastructure of the juxtaglomerular apparatus in five adult male Cebus apella monkeys and communicate morphometric data of the macula densa.In comparison with several species of rodents examined before, the macula cells of the monkey contain many more mitochondria and possess a particularly thick basal membrane. The relative volume of the nuclei is slightly smaller than in rodents.The Goormaghtigh cells of the monkey resemble those of the other animals investigated.The epithelioid (or juxtaglomerular) cells do not contain secretory granules. This observation reminds one of the behavior of the epithelioid cells of guinea pigs.Dedicated to Professor Dr. med. G. Petry (Marburg/Lahn) on the occasion of his 65th birthdayThe authors wish to thank Professor Dr. G. Peters, Head of the Institute of Pharmacology, and Professor Dr. F. Roch-Ramel for kindly having provided the monkey kidneys     

The normal juxtaglomerular apparatus in the human kidney. A morphological study.

Out of 49 serially studied juxtaglomerular apparatuses, 6 typical variants from two normal human kidneys were reconstructed graphically. The agranular Goormaghtigh cells filled the entire space between the macula densa, the afferent and the efferent arterioles and the glomerular mesangium. The Goormaghtigh cells were always in direct contact with all the other structures. They also invariably continued into the glomerular mesangium. The distal tubule regularly showed widening in the macula densa segment and, at this level, there was considerable variation in the shape of the distal tubule. Direct contact between the macula densa and the hilar arterioles was not always present, the area of contact was usually greater with the afferent than with the efferent arteriole.     

Ultrastructure of the juxtaglomerular apparatus of the kidney and of the peripolar cells in the sand lizard (Lacerta agilis)

In 9 sand lizards ultrastructure of the juxtaglomerular complex of the kidney has been studied. It is presented as juxtaglomerular cells, situating in the middle tunic of the afferent glomerular arteriole near the vascular pole of the renal corpuscle. Cytoplasm of these cells contains secretory granules at various stages of development: young, maturing and mature, as well as solid corpuscles and myofilaments. In some nephrons primitive forms of the macula densa and the juxtaglomerular island occur. Their presence demonstrates phylogenetically new structural organization of the juxtaglomerular complex in lizards. For the first time in reptilia peripolar cells are found, they are situated on the basal membrane of the external part of the glomerular capsule near the vascular pole of the renal corpuscle. A suggestion is made on their functional interconnection with the juxtaglomerular complex.     

The juxtaglomerular apparatus in the mesonephros of Newt (Triturus cristatus)

Summary 1)As in mammals, the juxtaglomerular apparatus of the Newt (Triturus cristatus) is composed by cells of the media of the afferent glomerular arteriole and by cells of the intermediary tubule. 2) The cells of the media of the glomerular arteriole are of two different types: granular and agranular cells. 3) The intermediary tubule is formed by dark and light cells. 4) Part of interrenal body is located close to glomerular arteriole and intermediary tubule.This work was supported by grant of Consiglio Nazionale delle Ricerche of Italy (C.N.R.) N. 115/815/04677.     

Innervation opf the juxtaglomerular complex (JGC) of the kidney in vertebrates

On the base of electron microscopic investigations of kidneys, performed on some representatives of vertebrata (fishes, amphibia, reptiles, birds, mammalia) the data on their JGC innervation are presented. In the course of evolution the structure of nervous-muscular, nervous-endocrine and nervous-epithelial contacts becomes more complex. The role of the nervous factor in regulation of the systemic blood flow and water-salt metabolism acquires a greater significance in the process of development.     

Purification and properties of prolylcarboxypeptidase (angiotensinase C) from human kidney.

Prolylcarboxypeptidase was purified from human kidney 1200-fold with 18% yield. The enzyme had no cathepsin A activity and appeared to be homogeneous in gel electrophoresis. The molecular weight of prolylcarboxypeptidase was estimated to be 115,000 by gel filtration. Under denaturing conditions the enzyme dissociated into subunits of 45,000 and 66,500 molecular weight. The enzyme cleaved benzyloxycarbonyl (Cbz)-Pro-Phe, representing the COOH-terminal end of angiotensin II and des-Asp1-angiotensin II (angiotensin III), at a rate of 31 micronmol/h/mg of protein. The rate of hydrolysis increased when phenylalanine in the N-protected dipeptide was replaced with alanine, valine, or leucine or when the octapeptide angiotensin II or the heptapeptide angiotensin III were the substrates. The enzyme also cleaved the angiotensin II antagonist saralasin (Sar1-Ala8-angiotensin II). The Km values were 1 mM, 2mM, and 0.77 mM with Cbz-Pro-Phe, angiotensin II, and angiotensin III, respectively. The enzyme had an acid pH optimum (4.5 to 5.5), but hydrolyzed angiotensin III at pH 7 at 50% of the optimal rate. Prolylcarboxypeptidase was inhibited by diisopropyl phosphorofluoridate and pepstatin, but not by sequestering agents or -SH reagents.     

Immunohistochemical localization of type IV collagen fibronectin and laminin in the juxtaglomerular apparatus of the rat kidney

The juxtaglomerular apparatus (JGA) is a complex structure containing several components: the vessels, the extraglomerular mesangium and the distal tubule. These structures include cellular elements and an extracellular matrix (ECM). Collagenous (type IV collagen) and noncollagenous components of the basement membranes were studied. The localization of type IV collagen and of two extracellular glycoproteins (laminin and fibronectin) was investigated using immunofluorescent and immunoperoxidase labelled antibodies. Type IV collagen and laminin have the same localization on the JGA basement membranes. On the other hand, fibronectin is limited to the entrance of the glomerular stalk. On electron microscopy, type IV collagen is found in the basement membrane while fibronectin is restricted to certain areas of the extracellular matrix. These findings confirm data concerning the distribution of these three components in basement membranes and allow a better understanding of the histoarchitecture of the juxtaglomerular apparatus.