Structure of the Bufo arenarum kidney: renal corpuscle, neck segment and proximal tubule.
ABSTRACT The structural organization of the renal corpuscle (RC), ciliated neck segment (NS) and the proximal tubule (PT) were studied in the toad, Bufo arenarum, by means of light and transmission electron microscopy. The ciliated neck segment and the proximal tubule are located in the dorsolateral zone of the kidney, while the distal tubules are located in a ventromedial zone. RC are found between these two zones. The glomerular filter apparatus consists of the podocyte epithelium, a basement membrane, a subendothelial space and an endothelium. The podocyte emits cytoplasmatic processes extending over the surface of the glomerular capillaries. These processes divide into further processes ending in expansions known as pediceles. The basement membrane consists of a lamina rara externa and a rather thin lamina densa, while the subendothelial space contains collagen fibers and slender cytoplasmic processes of the mesangial cells. NS are composed of ciliated cells with a characteristic location of the mitochondria. The PT consists of prismatic cells with a dense luminal brush border of long microvilli and numerous apical vesicles. The basal cell membrane is increased by small infoldings. One characteristic structure of the cytoplasm is the presence of lipid droplets. The cytological structure of PT cells can be considered as an adaptation for the reabsorption of organic materials.
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ABSTRACT: This study deals with the morphology and ultrastructure of the mesonephros in adult caecilians of the species Geotrypetes seraphini. Based on serial sections in paraffin and araldite, nephrons are reconstructed and the cellular characteristics of different nephron segments described. The long and slender mesonephric kidneys of G. seraphini are broadest caudally and taper toward the front, where the organs are divided into smaller segmental divisions. Two nephron types can be distinguished on the basis of their connections to the coelom and their position within the nephric tissue: ventral nephrons connect to the coelom via a ciliated peritoneal funnel, whereas medial nephrons lack this connection. Both nephron types are composed of a filtration unit, the Malpighian corpuscle, and a renal tubule, which can be divided into six morphologically distinct segments: neck segment, proximal tubule, intermediate segment, early distal tubule, late distal tubule, and collecting tubule. Collecting tubules merge and form a branch system that opens into collecting ducts. Collecting ducts empty into the Wolffian duct. Proximal tubules of nephrons in the frontal divisions are morphologically different from the proximal tubules of more caudal kidney regions. Distal tubule subdivision is only clearly recognizable at the electron microscopic level. The length of each nephron segment is calculated from a ventral nephron with a total length of approximately 3.8 mm, and the course of the segments within the nephric tissue is reported. The number of nephrons was estimated at 1,700 units in each kidney. The segmentation and ultrastructure of the mesonephric nephrons in G. seraphini are discussed in relation to nephron descriptions from other caecilians and we further discuss the evolutionary origin of the amphibian nephron.Journal of Morphology 12/2004; 262(2):583-607. · 1.60 Impact Factor
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ABSTRACT: The capacity for protein reabsorption in the renal proximal tubule (PT) were studied in Rana temporaria frogs by separate, simultaneous and sequential introduction of yellow fluorescent protein (YFP) and green fluorescent protein (GFP). The uptake patterns of YFP and GFP in PT epithelial cells were investigated 15-120 min after their bolus intravenous and intraperitoneal injection. As shown by confocal microscopy, the tubular uptake of YFP and GFP was time- and dose-dependent. These proteins are absorbed in similar way and can be accumulated in the same endocytic vesicles after their combined injections. When GFP was injected 30 and 90 min before YFP, and vise versa, the number of vesicles with pre-injected protein increased and the percentage of vesicles with colocalized GFP and YFP reduced. At the same time, the uptake rate of a protein injected later progressively and significantly decreased. Subcellular localization of endocytic receptors, megalin and cubilin, in renal PT cells after intravenous YFP introduction were revealed by immunofluorescent microscopy. Colocalization of internalized YFP with megalin or cubilin in the endocytic vesicles was demonstrated. The data suggest the possibility of protein uptake by receptor-mediated endocytosis and the existence of a mechanism limiting the protein absorption rate in wintering frogs.Comparative biochemistry and physiology. Part A, Molecular & integrative physiology 05/2013; · 2.20 Impact Factor
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ABSTRACT: The renal tubular uptake of green fluorescent protein (GFP) in frog Rana temporaria was studied by laser confocal microscopy. The specific green fluorescence was revealed in the proximal tubule cells 30 min after intravenous GFP injection. The GFP fluorescence was distributed predominantly in the apical part of the cytoplasm in the form of the intensively fluorescing vesicles. The GFP injections increased dose-dependently the GFP tubular uptake. This was confirmed by the quantitative assessment of intensity of the specific fluorescence, its relative vesicular density, and by correlation analysis. Preliminary administration of arginine vasotocin into the dorsal lymphatic sac decreased significantly the GFP absorption. The effect of arginine vasotocin was inhibited by pretreatment a vasopressin V1-receptor antagonist. These results suggest that a decrease in the GFP absorption is due to a fall of the AVT-dependent glomerular filtration rate and consequently a decrease in the filtered GFP amount. The effect of arginine vasotocin on the GFP absorption seems to be mediated via the V1-like receptors of preglomerular blood vessels.Zhurnal evoliutsionnoĭ biokhimii i fiziologii 01/2011; 47(1):54-61.