Luciano Barajas

The innervation of the juxtaglomerular apparatus and surrounding tubules: A quantitative analysis by serial section electron microscopy

In electron micrographs of serial sections of a rat juxtaglomerular apparatus “axon segments” were analyzed for contact with the cells of the vascular component and surrounding tubules. Slightly less than one-fourth of the cells of the vascular component were innervated. Nerve endings were seen on less than one-third of the cells of the afferent arteriole and about one-third of the cells of the efferent arteriole. The mesangial region had only 3 of its 30 cells innervated. Of these 3 cells, 2 were in contact with the distal tubule. The majority of the innervated cells were contacted by nerve endings belonging to more than one axon segment. Frequently en passant nerve endings from the same axon were seen to contact several different cells (granular and agranular) of the vascular component. Individual axons also established en passant contact with granular and agranular cells of the vascular component and tubular cells. These findings support the view that the neural effect on renin secretion is t the result of a complex response to neural activity which includes, besides direct action on granular cells, indirect action mediated through its effect on arteriolar and renal tubular systems.

Effect of modifications in conformation of protein molecules on structure of mitochondrial membranes.

New methods for preparing tissues for electron microscopy were worked out with the aim of limiting as far as possible conformational changes in the protein molecules. The proteins were stabilized by intermolecular cross-linking with glutaraldehyde, dehydrated by short treatment with ethylene glycol, and embedded in Vestopal W or in hydroxypropylmethacrylate. Such treatment appeared to affect the native conformation of proteins less than dehydration by means of air drying with or without previous cross-linking. The mitochondrial membrane elements showed a particulate structure with a range of dimensions of the particles which closely corresponds to that of membrane proteins as judged from their molecular weights. A rectangularly shaped particle measuring 60 × 100 A was frequently observed in the mitochondrial membranes. Intentional denaturation of the tissue by heat or low pH resulted in a membrane structure similar to that observed in conventionally prepared tissues. The results conform with the concept that cellular membranes consist of a two-dimensional array of globular protein molecules and lipoprotein complexes. A continuous light layer of uniform thickness which characterizes the unit membrane structure and which has been interpreted as consisting of a continuous lipid bilayer could be observed only after extensive denaturation of the membrane proteins. The triple-layered unit membrane pattern of membranes, therefore, appears to be the result of extensive denaturation of membrane proteins.

Electron microscopic and histochemical evidence for a tubular innervation in the renal cortex of the monkey

An innervation of the tubules of the monkey renal cortex has been demonstrated by electron microscopy. At the light microscopic level, histochemical methods showed the existence of both adrenergic and cholinergic nerve fibers in association with the renal tubules. By electron microscopy, bundles of terminal varicose axons were observed traveling between the blood vessel and tubules. Nerve endings in these bundles established contact with the basement membranes of both proximal and distal tubules as well as smooth muscle cells of the arterioles. Small bundles of axons having little or no Schwann cell covering were seen running between the tubules. Varicosities of these axons make contact with proximal and distal tubular cell basement membranes. By light microscopy adrenergic and cholinergic terminal axons were seen in close association with proximal and distal tubules. Serial sections showed that the tubular nerve endings are part of the perivascular nerve bundles or originate from them and travel independently for variable distances among the tubules. These studies provide an anatomical basis for a direct action of the autonomic nervous system on renal tubular function.

The development and ultrastructure of the juxtaglomerular cell granule

Juxtaglomerular apparatuses from normal rats and monkeys, from patients with renovascular hypertension and from rats with constricted renal arteries were studied with the electron microscope. The juxtaglomerular cell granule appears to arise from protogranules with a crystalline pattern having a periodicity which, in different crystals, varies from 50 to 100 A. Protogranules, about 90–400 mμ long, are seen within the dilated cisternae of the Golgi apparatus. They present variable contours, from a round to a diamond shape. A species difference regarding the shape and the density of the protogranules is noticed. Near the Golgi apparatus multiple protogranules and small vesicles are contained in large smooth-surfaced membranous sacs. Coalescence of protogranules within large smooth-surfaced sacs results in an irregularly shaped conglomerate in which the protogranules retain their individual and independently oriented crystalline patterns. The mature granules, known from light microscopy, may be formed from these conglomerates or from a single protogranule. Crystalline patterns may persist in fully developed granules, although these usually lack crystalline patterns. Crystalline protogranules appear more abundant in the granular cells from rat and human kidneys with narrowed renal arteries. This abundance could be related to increased synthesis of the secretory product which is thought to be renin.

A new model for mitochondrial membranes based on structural and on biochemical information

On the basis of recent electron microscopic observations by Sjostrand and Barajas23 and available biochemical information, a model describing the molecular structure of mitochondrial membranes was designed. In addition to accounting for the structural features of those membranes as revealed by electron microscopy, this model also pays due attention to the fact that a large number of enzymes and electron carrier molecules are basic components of the membranes. The fundamental justification for such a model which is to assist in an understanding of membrane function is satisfied as far as general principles are concerned. The other justification of such a model concept is to allow predictions regarding additional properties of the membrane. Such predictions have made it possible to design future experiments which can add further information regarding the molecular structure of cellular membranes.

The ultrastructure of the juxtaglomerular apparatus as disclosed by three-dimensional reconstructions from serial sections: The anatomical relationship between the tubular and vascular components

The area of contact between the tubular and vascular components of the juxtaglomerular apparatus has been investigated by means of serial section electron microscopy and three-dimensional reconstruction. Series of 500 serial sections were used. Sequential montages of electron micrographs were analyzed. The distribution of the surface of contact between the distal tubule and the different parts of the vascular components was measured. An extensive constant contact between the distal tubule and both the extraglomerular mesangial region and efferent arteriole was found. In one juxtaglomerular apparatus, no contact between granular cells and distal tubule was found throughout the three-dimensional reconstruction. In the others it varied in extent and location. Two types of contact are described: one represented by simple apposition of basement membranes, which is interpreted as reversible; and another type of contact anatomically more complex, which is interpreted as irreversible. This might have a bearing on current theory on the control of renin secretion.

Three-dimensional reconstruction of Pityrosporum yeast cells based on serial section electron microscopy

The purpose of this communication is to direct attention to the complex architecture of Pityrosporum orbiculare and the quantitative relationship between the various cytoplasmic organelles. Cultured cells fixed in glutaraldehyde and potassium permanganate solutions and embedded in Vestopal were sectioned serially. Fifty or more consecutive sections were mounted on Formvar-coated single-hole grids for electron microscopy. Electron micrographs were taken of complete cells. The volume of the organelles was estimated as a percentage of the cytoplasm. About one-third of the cells was occupied by the nucleus, light bodies, and the mitochondria. The quantitative expression showed little variability between the three cells examined. Other features, too small and irregular for quantitative expression, were found to present similar patterns of arrangement in the serially sectioned material. There were two systems of cytomembranes. One, peripherally located near the cell wall, was a system of folds, lacunae, and small vesicles. The second, more centrally located, was a system of lacunae expanding to enclose dense material. Serial section electron microscopy can be utilized for quantitative measurements of organelles. It is also useful for placing small units, such as the nuclear buds and structures formed by the cytomembranes in respect to the cell as a whole. This is the first report, to our knowledge, in which whole unicellular organisms have been analyzed quantitatively by serial section electron microscopy. The same methods could be applied to the study of other unicellular organisms.

Juxtaglomerular Cell Tumor

A 15-year-old female with primary reninism presented with benign hypertension, normokalemia, normal aortagram and normal intravenous pyelogram. The diagnosis was suggested only by a remarkably elevated plasma renin activity (PRA). Selective catheterization of renal vein branches was necessary to make the diagnosis of a tumor. A local resection of the tumor resulted in normalization of blood pressure and PRA. Prior to the definitive surgery, oral propranolol was effective in lowering PRA and blood pressure.

Expression of epidermal growth factor in the rat kidney

SummaryThe renal localization and the site of synthesis of epidermal growth factor (EGF) were investigated in the rat kidney by immunohistochemistry and in situ hybridization techniques. EGF was localized in the cells of the thick ascending limb of Henle (TAL) and distal convoluted tubule (DCT). At the ultrastructural level, EGF immunoreactivity was distributed on the apical membrane and trans-Golgi complex of the TAL and DCT cells. These segments of the rat nephron also hybridized to prepro-EGF cRNA probes in a specific manner, indicating that TAL and DCT are the sites of EGF synthesis in the rat kidney.

Ultrastructural localization of acetylcholinesterase in the renal nerves

Acetylcholinesterase activity is present in the renal nerves of the monkey. At the ultrastructural level the precipitate appears extracellularly around axons and varicosities. No linear deposits at the area of contact between the nerve endings and the effector cells were observed. The density of the deposits is more pronounced around the axons than around the varicosities. This pattern is shared by all nerves present around a given arteriole. The topographic distribution and extent of acetylcholinesterase-positive innervation observed by electron microscopy corresponds to those of the catecholamine-containing fibers observed by the fluorescent histochemical technique. This and the fact that in some animals all the nerves observed are acetylcholinesterase-positive leads us to believe that most of them are adrenergic but rich in acetylcholinesterase.