Morphometric study of the ultrastructure of nephrons and collecting tubules in the kidney of rats with renal and spontaneous hypertension.

The convoluted proximal and straight distal tubules and the medullary collecting ducts in kidneys of rats with ischaemic renal hypertension and with genetic spontaneous hypertension were studied by means of electron microscopic morphometry. The volume of mitochondria, the area of their cristae, of the outer surface and of membranes of the intercellular labyrinth, and other ultrastructural characterisitcs were calculated. No significant differences were found in proximal tubules between experimental and control animals, although in the distal tubules in both experiments the coefficient characterizing the level of morphologic organization of mitochondria, which takes into account their basic morphometric parameters, was reduced in hypertensive animals as compared with the intact ones. The volume of mitochondria and the area of their cristae in collecting ducts, and also the area of membranes of the intercellular labyrinth were increased. Our results suggest that in hypertension the reabsorption of substances from the proximal tubules is essentially normal, that it is reduced at the beginning of the distal tubules but is intensified in the collecting ducts.     

Structural and functional changes in the mitochondrial apparatus of cortical tubules of the solitary kidney in chronic blockade of cholinergic mediation

In 15, 30 and 90 days the effect of continuous atropine pharmacological blockade of parasympathetic innervation on morphometrical characteristics of epithelial mitochondria in the cortical segments of the canaliculi has been studied in a single kidney of Wistar rats. The maximal degree of the alternative changes has been determined in the proximal canaliculi. In the distal canaliculi epithelium a compensatory increase of the main quantitative parameters in mitochondria has been registered. The plasticity of the mitochondrial apparatus, specific for the collecting tubules under compensatory hypertrophy, is inhibited under conditions of deparasympathization.     

Structure of the kidney in the crab-eating frog, Rana cancrivora

The structure of the nephron in the ranid frog, Rana cancrivora, was studied by light and electron microscopy. This frog is the only amphibian species to live in mangrove swamps of very high salinity. The nephron consists of the following parts: renal corpuscle, ciliated neck segment, proximal tubule, ciliated intermediate segment, distal tubule, connecting tubule, and collecting duct. The distal tubule is located in the ventromedial region of the kidney, and the other tubules are situated in the dorsolateral region. Renal corpuscles are found between the two regions. Some renal corpuscles have a wide Bowman's space because of the small glomerulus within them. The proximal tubules are composed of columnar cells with a dense luminal brush border of long microvilli and numerous apical vesicles and vacuoles. The initial part of the distal tubule consists of heavily interdigitated cells, characterized by a very regular palisade arrangement of mitochondria. In the terminal part of the distal tubule, shorter mitochondria of the infolding cells are situated irregularly around the nucleus. The connecting tubule consists of principal cells and canaliculus cells. The collecting duct consists of columnar or cuboidal cells; cytoplasmic organelles are relatively sparse. The canaliculus cells are intercalated between principal cells from the terminal distal tubule to the proximal part of the collecting duct. Our findings indicate that the kidney of R. cancrivora is structurally similar to kidneys of other amphibians. These findings are discussed with regard to probable correlations between ultrastructure and function in R. cancrivora.     

Morphology of the kidney of adult bowfin, Amia calva, with emphasis on "renal chloride cells" in the tubule

The nephron of adult bowfin, Amia calva, was described using light and electron microscopic techniques. The kidney of the bowfin possesses an abundant supply of renal corpuscles with each consisting of a glomerulus and a Bowman's capsule of visceral (podocyte) and parietal layers. No juxtaglomerular apparatus is present. The epithelium of the tubule is continuous with the parietal epithelium and is divisible in descending order into neck, first proximal, second proximal, first distal, second distal, and collecting segments. The tubules drain into a complex system of collecting ducts that ultimately unite with the main excretory duct, the archinephric duct. Mucous cells are the dominant cell throughout the entire ductular system. Nephrostomes are dispersed along the kidney capsule. The neck segment has a ciliated epithelium, and while both proximal segments possess a prominent brush border, the fine structure of the first implies involvement in protein absorption and the second in the transport and reabsorption of solutes. The cells of the first distal segment are characterized by deep infolding of the plasma membrane and a rich supply of mitochondria suggesting the presence of a mechanism for ion transport. The second distal segment is composed of cells resembling the chloride cells of fishes and these cells are present in progressively decreasing numbers in the collecting segment and duct system so that only a few are present in the epithelium of the archinephric duct. The "renal chloride cells" possess an abundant network of smooth tubules and numerous mitochondria with a rich supply of cristae. Glycogen is also a conspicuous component of these cells. The presence of "renal chloride cells" in this freshwater holostean, in other relatively primitive freshwater teleosts, and in larval and adult lampreys is discussed with reference to both phylogeny and the need for a special mechanism for renal ion conservation through absorption.     

Ultrastructure and osmoregulatory function of the kidney in larvae of the Persian sturgeon Acipenser persicus

The localization of Na(+) , K(+) -ATPase (NKA) and the ultrastructural features of kidney were examined in larvae of the Persian sturgeon Acipenser persicus (L 31-41 mm total length and 182·3-417·3 mg). Investigations were conducted through light and electron microscopy and through immunofluorescence for NKA detection. The kidney nephrons consisted of a large glomerulus and tubules (neck, proximal, distal and collecting), which connected to the ureters. Posteriorly, ureters extended and joined together into a thin-walled ureter terminal sac. Ultrastructurally, the glomerular cells (podocytes) possessed distinctive pedicels that extended to the basal membrane. The proximal tubule (PT) showed two different cells. The cells lining the anterior part of PT possessed apical tall microvilli (c. 2·7 μm), a sub-apical tubular system, a basal nucleus and dense granules. Posteriorly in the cells, the sub-apical tubular system and granules were absent and round mitochondria associated with basolateral infoldings were found; the apical microvilli were reduced. Distal and collecting tubular cells showed the typical features of osmoregulatory cells, i.e. well-developed basolateral infoldings associated with numerous mitochondria. No immunofluorescence of NKA was detected in the glomeruli. A weak immunostaining was observed at the basolateral side of the cells lining the neck and PT. A strong immunostaining of NKA was observed in the entire cells of the distal tubules, collecting tubules and in some isolated cells of the ureters. In all immunostained cells, the basolateral region showed a much higher fluorescence and nuclei were immunonegative. In conclusion, the epithelial cells of kidney tubules had morphological and enzymatic features of ionocytes, particularly in the distal and collecting tubules. Thus, the kidney of A. persicus larvae possesses active ion exchange capabilities and, beside its implication in excretion, participates in osmoregulation.     

Carbonic anhydrase in the monkey kidney

The distribution of carbonic anhydrase in the kidney of the cynomolgus monkey was studied by the histochemical method of Hansson. Glomeruli and Bowman's capsule were inactive. Convoluted proximal tubules showed high enzyme activity at the brush border and the basolateral membranes and the cytoplasm. Straight proximal tubules were less intensely stained. In nephrons with long loops of Henle, the descending thin limb contained weak enzyme activity, whereas the ascending thin limb was inactive. The thick limb of Henle's loop displayed most enzyme activity at the luminal cell border. In distal convoluted tubules enzyme activity was restricted to the basal part of the cells. In the late distal tubule, intercalated cells appeared among the "ordinary" distal cells and contained abundant cytoplasmic enzyme. Many intensely stained intercalated cells were also found in the cortical and outer medullary segments of the collecting duct, intermingled with more weakly stained chief cells. In the inner medullary segment of the collecting duct, enzyme activity gradually disappeared. Many capillaries were clearly stained for enzyme activity. The capillary staining apparently varied with that of the kidney tubules; virtually all capillaries in the cortex, but very few in the inner medulla, were stained. The distribution of carbonic anhydrase in the kidney tubules of the monkey is very similar to that in man and in the rat, but the primate kidney differs from the rat kidney by the presence of capillary enzyme activity. The functional importance of this difference is not clear at present.     

Peanut and Lotus tetragonolobus binding sites in human kidney from congenital nephrotic syndrome of Finnish type

The authors have studied kidney tissues from two cases of Congenital Nephrotic Syndrome of Finnish Type (CNS:FT), two cases of infantile polycystic disease and five normal newborns using Peanut (PNA) and Lotus Tetragonolobus (LTA) peroxidase-labeled lectins. In CNS:FT a positive reaction for LTA has been documented at the luminal surface of the microcysts, while no staining was observed with PNA. In infantile polycystic disease the cysts were stained by PNA, whereas LTA binds selectively proximal undilated tubules. In normal kidney distal tubules as well as collecting ducts and proximal tubules were stained by PNA and LTA respectively. The results suggest that in CNS:FT microcystic transformation of the kidney can originate from proximal tubules according to microdissection studies elsewhere reported.     

Cellular differentiation in the kidneys of newborn mice studies with the electron microscope

The structure of the kidney of the Swiss albino mouse changes progressively during the first 2 weeks after birth. Cells proliferate to form new nephrons, cells differentiate by acquiring specialized membranous components, and certain cytological features which are present at birth diminish in abundance or disappear. The differentiation of the cells of the cortical tubules has been studied using the light and electron microscopes. The tubules are partially and variably differentiated at birth. During the first 2 weeks after birth the brush border develops in the proximal tubules by the accumulation of numerous microvilli on the apical cell margins. Basal striations develop in proximal and distal tubules as an alignment of mitochondria, the result of what appears to be progressive interlocking of adjacent fluted cells. The mitochondria increase in number and size, accumulate homogeneous matrix, and acquire small, very dense granules. The collecting ducts develop tight pleating of the basal cell membranes, and dark cells containing numerous small cytoplasmic vesicles and microvilli appear. At birth there are dense irregular cytoplasmic inclusions presumed to be lipide in renal cells, the cytoplasmic granules of Palade are abundant, and there are large round bodies in the cells of the proximal tubules. The lipide inclusions disappear a few days after birth, and the cytoplasmic granules of Palade diminish in abundance as the cells differentiate. The large round bodies in the proximal tubules consist of an amorphous material and contain concentrically lamellar structures and mitochondria. They resemble the cytoplasmic droplets produced in the proximal tubules of adult rats and mice by the administration of proteins. The large round bodies disappear from the proximal tubules of infant mice during the first week after birth, but the concentric lamellar structures may be found in adult mice.     

CELLULAR DIFFERENTIATION IN THE KIDNEYS OF NEWBORN MICE STUDIED WITH THE ELECTRON MICROSCOPE

The structure of the kidney of the Swiss albino mouse changes progressively during the first 2 weeks after birth. Cells proliferate to form new nephrons, cells differentiate by acquiring specialized membranous components, and certain cytological features which are present at birth diminish in abundance or disappear. The differentiation of the cells of the cortical tubules has been studied using the light and electron microscopes. The tubules are partially and variably differentiated at birth. During the first 2 weeks after birth the brush border develops in the proximal tubules by the accumulation of numerous microvilli on the apical cell margins. Basal striations develop in proximal and distal tubules as an alignment of mitochondria, the result of what appears to be progressive interlocking of adjacent fluted cells. The mitochondria increase in number and size, accumulate homogeneous matrix, and acquire small, very dense granules. The collecting ducts develop tight pleating of the basal cell membranes, and dark cells containing numerous small cytoplasmic vesicles and microvilli appear. At birth there are dense irregular cytoplasmic inclusions presumed to be lipide in renal cells, the cytoplasmic granules of Palade are abundant, and there are large round bodies in the cells of the proximal tubules. The lipide inclusions disappear a few days after birth, and the cytoplasmic granules of Palade diminish in abundance as the cells differentiate. The large round bodies in the proximal tubules consist of an amorphous material and contain concentrically lamellar structures and mitochondria. They resemble the cytoplasmic droplets produced in the proximal tubules of adult rats and mice by the administration of proteins. The large round bodies disappear from the proximal tubules of infant mice during the first week after birth, but the concentric lamellar structures may be found in adult mice.     

Peanut and Lotus tetragonolobus binding sites in human kidney from congenital nephrotic syndrome of finnish type

Summary The authors have studied kidney tissues from two cases of Congenital Nephrotic Syndrome of Finnish Type (CNS:FT), two cases of infantile polycystic disease and five normal newborns using Peanut (PNA) and Lotus Tetragonolobus (LTA) peroxidase-labeled lectins.In CNS:FT a positive reaction for LTA has been documented at the luminal surface of the microcysts, while no staining was observed with PNA. In infantile polycystic disease the cysts were stained by PNA, whereas LTA binds selectively proximal undilated tubules. In normal kidney distal tubules as well as collecting ducts and proximal tubules were stained by PNA and LTA respectively.The results suggest that in CNS:FT microcystic transformation of the kidney can originate from proximal tubules according to microdissection studies elsewhere reported.This work was supported by M.P.I. (Rome)     

Morphometric parameters of nutria kidney structures in postnatal ontogeny

Data on the morphometric parameters of the renal corpuscle, renal tubules, and collecting ducts of male and female nutrias in postnatal ontogenesis were obtained. It was found that the area of the renal corpuscle, glomerulus, the cavity and lumen of the capsule, and the proximal tubule diameter in the right and left kidney of female and male nutrias in the first year of life increase. The distal tubule diameter also increases; however, the dynamics of its changes becomes sinuous after 4.5 months. The collecting duct diameter varies depending on gender, age, and renal topography. The nuclear-cytoplasmic ratio in the cells of proximal and distal tubules and collecting ducts changes in a sinuous manner and depends on the gender and age of nutrias. The minimum mean value of the nuclear-cytoplasmic ratio was found in the proximal tubule cells in the left kidney of 12-month-old female nutrias (0.162 ± 0.002), and the maximum value was found in the distal tubule cells in the left kidney of newborn male nutrias (0.435 ± 0.007).     

Immunocytochemical localization of gamma-glutamyl-transferase on isolated renal cortical tubular fragments

The localization of gamma-Glutamyltransferase (gamma-GT, E.C.2.3.2.2) was studied on isolated tubular fragments from rat kidney cortex immunocytochemically. Monospecific antibodies raised in the goat against rat kidney gamma-GT were used. Antigoat immunoglobulin from the rabbit conjugated with ferritin was used for visualisation of the antibody binding sites. The enzyme was found to be localized at the brush border membrane of proximal tubules, the luminal membrane of distal tubules and collecting duct segments. The enzyme could further be localized on the antiluminal or basolateral cell membranes of proximal and distal tubular fragments, whereas no such localization was verified for collecting duct segments. The role of this basolateral gamma-GT localization in context with the kidney's ability to extract over 83% of the renal arterial glutathione (GSH) input during a single passage is discussed.     

Expression of Bcl-2 and Bax in mouse renal tubules during kidney development

Bcl-2 and Bax play an important role in apoptosis regulation, as well as in cell adhesion and migration during kidney morphogenesis, which is structurally and functionally related to mitochondria. In order to elucidate the role of Bcl-2 and Bax during kidney development, it is essential to establish the exact location of their expression in the kidney. The present study localized their expression during kidney development. Kidneys from embryonic (E) 16-, 17-, 18-day-old mouse fetuses, and postnatal (P) 1-, 3-, 5-, 7-, 14-, 21-day-old pups were embedded in Epon. Semi-thin serial sections from two E17 kidneys underwent computer assisted 3D tubule tracing. The tracing was combined with a newly developed immunohistochemical technique, which enables immunohistochemistry on glutaraldehyde fixated plastic embedded sections. Thereby, the microstructure could be described in detail, and the immunochemistry can be performed using exactly the same sections. The study showed that Bcl-2 and Bax were strongly expressed in mature proximal convoluted tubules at all time points, less strongly expressed in proximal straight tubules, and only weakly in immature proximal tubules and distal tubules. No expression was detected in ureteric bud and other earlier developing structures, such as comma bodies, S shaped bodies, glomeruli, etc. Tubules expressing Bcl-2 only were occasionally observed. The present study showed that, during kidney development, Bcl-2 and Bax are expressed differently in the proximal and distal tubules, although these two tubule segments are almost equally equipped with mitochondria. The functional significance of the different expression of Bcl-2 and Bax in proximal and distal tubules is unknown. However, the findings of the present study suggest that the mitochondrial function differs between mature proximal tubules and in the rest of the tubules. The function of Bcl-2 and Bax during tubulogenesis still needs to be investigated.     

Comparison of the distribution of tissue kallikrein and esterase A, a kallikrein-like enzyme, in rat kidney using specific monoclonal antibodies

Tissue kallikrein (E.C. 3.4.21.35) and arginine esterase A, another closely related, kinin-generating serine protease, have been localized by immunocytochemistry in rat kidney, using monoclonal antibodies that do not crossreact with other kallikrein-related enzymes or with tonin. Kallikrein was present primarily in the apical cytoplasm of the connecting tubule and the cortical collecting duct. Esterase A, on the other hand, was present primarily in the basolateral region of both proximal and distal straight tubules in the outer medulla and medullary rays. In addition, esterase A was demonstrable in distal convoluted tubules and, to a lesser extent, in proximal convoluted tubules. The presence of different kinin-generating enzymes at these sites would permit the formation of kinins from appropriate substrates on both the vascular and luminal poles of separate segments of the kidney tubule.     

Ultrastructure of the kidney of the newt

In the newt [Triturus vulgaris (J.)] kidney a zone of single nephrons is distinguished, where there are ten nephrons, connected with the paramesonephral (Müller's) canal, and another zone of the renal mass; in the latter the main part of nephrons is situated, which are connected with the ureter by means of collecting tubules. In these zones of the kidney ultrastructure of epitheliocytes in the proximal and distal parts is different. The renal corpuscles of the epithelial cell in the cervical and in the intermediate parts are similar in both zones. In the zone of the single nephrons a specific peculiarity of epitheliocytes in the proximal and in the distal parts of the canaliculi is presence of numerous secretory granules in their cytoplasm. The canalicular epitheliocytes in the renal mass zone are different in the terminal and in the initial parts of the canaliculi: the former contains more mitochondria, and the area of the basolateral parts of plasmolemma is greater than those in the latter. These results are in accordance with the level of sodium ions transport in these parts of the canaliculus.     

Ghrelin receptors are expressed by distal tubules of the mouse kidney

Ghrelin, a peptide hormone from the stomach, has been recently discovered to reduce sodium excretion from the kidney. Although the effects on the kidney suggest actions in the distal nephron, the sites of expression of ghrelin receptors have not been localised. In the present work we have used a mouse that expresses green fluorescent protein under the control of the ghrelin receptor promoter to locate sites of receptor expression in the kidney. Receptor expression was confined to the straight parts of the distal tubules and the thin limbs of the loops of Henle. No expression was detected in other structures, including the glomeruli, proximal tubules and collecting ducts. Ghrelin receptors were not found in extra-renal or intra-renal arteries, despite observations that ghrelin is a vasodilator. The distribution revealed by in situ hybridisation histochemistry was the same as that revealed by the reporter. In conclusion, ghrelin receptors have a restricted distribution in the kidney. The location in the straight parts of the distal tubules accords with observations that ghrelin promotes sodium retention.     

Immunoexpression of aquaporins 1, 2, 3 and 4 in kidney of yak (Bos grunniens) on the Qinghai-Tibetan Plateau

Aquaporins (AQP) 1, 2, 3 and 4 belong to the aquaporin water channel family and play an important role in urine concentration by reabsorption of water from renal tubule fluid. Renal AQPs have not been reported in the yak (Bos grunniens), which resides in the Qinghai Tibetan Plateau. We investigated AQPs 1?4 expressions in the kidneys of Yak using immunohistochemical staining. AQP1 was expressed mainly in the basolateral and apical membranes of the proximal tubules and descending thin limb of the loop of Henle. AQP2 was detected in the apical plasma membranes of collecting ducts and distal convoluted tubules. AQP3 was located in the proximal tubule, distal tubule and collecting ducts. AQP4 was located in the collecting ducts, distal straight tubule, glomerular capillaries and peritubular capillaries. The expression pattern of AQPs 1?4 in kidney of yak was different from other species, which possibly is related to kidney function in a high altitude environment.     

Mercuric chloride-induced alterations in stress protein distribution in rat kidney

Mercuric chloride (HgCl2) induces acute renal failure associated to tubular impairment in experimental animals and humans. Stress proteins are a superfamily of proteins, comprising heat- shock proteins (HSP) and glucose-regulated proteins (GRP), enhanced or induced in the kidney in response to stress. They act as molecular chaperones that protect organelles and repair essential proteins which have been denatured during adverse conditions. The involvement of stress proteins in mercury-nephrotoxicity has not yet been well clarified. This study was undertaken to detect the tubular distribution of four stress proteins (HSP25, HSP60, GRP75, HSP72) in the rat kidney injected with HgCl2 and to quantify lysosomal and mitochondrial changes in straight proximal tubules, the main mercury target. Sprague-Dawley rats were administered i.p. with progressive sublethal doses of HgCl2 (0.25 mg/kg, 0.5 mg/kg, 1 mg/kg and 3.5 mg/kg) or saline (as controls) and sacrificed after 24 h. In dosages over 0.50 mg/kg, stress proteins increased and changed localization in a dose-dependent manner. HSP25 was focally expressed in altered proximal tubules at 1 mg/kg but in the macula densa it was at 3.5 mg/kg. HSP60 and GRP75 were intense in the nucleus and cytoplasm of proximal tubules but moderate in distal tubules. HSP72 was induced in distal tubules after low exposures but in proximal tubules it happened at the highest dose. Moreover, a significant increase in lysosomal and total mitochondria (normal and with broken cristae) area and density were progressively found after HgCl2 treatments. Stress proteins could represent sensitive biomarkers that strongly correlate with the degree of oxidative injury induced by HgCl2 in the rat proximal tubules.     

Dopamine D4 receptor expression in rat kidney: evidence for pre- and postjunctional localization.

Dopamine D4 receptors mediate inhibition of vasopressin-dependent sodium reabsorption by dopamine in collecting tubules. At present, the distribution of D4 receptors in other renal districts remains an open issue. The renal distribution of D4 receptor was assessed in normally innervated and denervated male Sprague-Dawley rats by quantitative immunohistochemistry using an anti-dopamine D4 receptor rabbit polyclonal antibody. D4 receptor protein immunoreactivity was observed perivascularly in the adventitia and the adventitia-media border. The density of perivascular dopamine D4 receptor was higher in afferent and efferent arterioles than in other segments of the renal vascular tree. Renal denervation abolished perivascular dopamine D4 receptor protein immunoreactivity. In renal tubules, the epithelium of collecting tubules showed the highest dopamine D4 receptor protein immunoreactivity, followed by the epithelium of proximal and distal tubules. No dopamine D4 receptor protein immunoreactivity was observed in the epithelium of the loop of Henle. Denervation did not change dopamine D4 receptor protein immunoreactivity in renal tubules. These results indicate that rat kidney expresses dopamine D4 receptors located both prejunctionally and nonprejunctionally in collecting, proximal, and distal tubules. This suggests that the dopamine D4 receptor may be involved in the control of neurotransmitter release and in renal hemodynamic and tubule function.     

Modification of genital kidney nephrons for sperm transport in a plethodontid salamander,Eurycea longicauda

Salamanders possess kidneys with two distinct regions: a caudal pelvic portion and cranial genital portion. Nephrons of the pelvic region are responsible for urine formation and transport. Nephrons of the genital region transport sperm from testes to Wolffian ducts; however, nephrons of the genital region possess all the same functional regions found in pelvic kidney nephrons that are involved with urine formation and transport (renal corpuscles, proximal tubules, distal tubules, and collecting ducts). Morphological similarities between pelvic and genital regions stimulated past researchers to hypothesize that nephrons of genital kidneys possess dual function; that is, sperm transport and urine formation/transport. Considering size of glomeruli is directly related to the total amount of blood plasma filtered into the Bowman's space, we tested the hypothesis that nephrons of genital kidneys have reduced urine formation function by comparing glomerular size between nephrons of pelvic and genital kidney regions in Eurycea longicauda with general histological techniques. Light microscopy analysis revealed that glomeruli of pelvic kidneys were significantly larger than those measured from genital kidneys. Transmission electron microscopy analysis also revealed modifications in genital kidney nephrons when compared to pelvic kidney nephrons that suggested a decrease in urine formation function in genital kidneys. Such modifications included a decrease in basal and lateral plasma membrane folding in genital kidney proximal and distal tubules compared to that of pelvic kidney proximal and distal tubules. Genital kidney proximal tubules were also ciliated, which was not observed in pelvic kidney proximal tubules. In conclusion, although structurally similar at the histological level, it appears that nephrons of genital kidneys have decreased urine formation function based on glomerular size comparison and nephron ultrastructure.