Quantitative morphology of renal cortical structures during compensatory hypertrophy

The compensatory hypertrophy in different renal cortical structures was studied in rats 10 and 21 days after unilateral nephrectomy (UNX). Quantitative morphological/stereological analysis revealed significant increases in total renal cortical volume - 33% on day 10 and 48% on day 21 - after UNX. These changes were paralleled by significant increments in the volumes of proximal convoluted tubule (PCT, 55%), distal convoluted tubule (DCT, 114%), and cortical collecting duct (CCD, 106%) segments on day 10. The corresponding changes on day 21 were 76, 122, and 212%, respectively. These alterations were accompanied by increases in segment length; 3% PCT, 23% DCT, and 50% CCD on day 10 and 9% PCT, 30% DCT, and 142% CCD on day 21 after UNX. The total luminal and basolateral cell membrane surface areas also exhibited a time-dependent increase after UNX. The increments in both luminal and basolateral membrane domains in PCT and DCT after 10 days were not significant, but reached significance after 21 days (PCT: luminal membrane 21%, basolateral membrane 63%; DCT: luminal membrane 98%, basolateral membrane 63%). In contrast, CCD membrane areas had increased substantially already 10 days after UNX (luminal membrane 92%, basolateral membrane 71%). It declined subsequently by day 21 (luminal membrane 57%, basolateral membrane 32%). The cell rubidium concentration after a 30-second rubidium infusion, an index of Na-K-ATPase activity, as well as sodium concentrations were unaltered in cells of all nephron segments investigated. Altogether the stereological analysis shows that the compensatory increase in organ volume can be attributed primarily to an increase in nephron epithelial volume. The PCT responds with `radial' hypertrophy (thickening of the tubular epithelial wall), while the DCT undergoes `length' hypertrophy (increase of tubular length without thickening of the tubular wall and without an increase in number of cells). This type of hypertrophy is especially prominent on day 21 after UNX for the CCD which doubles in length. Only on day 10 does the CCD seem to respond with hyperplasia. Adaptive changes in response to UNX develop gradually. Only a few of the morphological parameters studied had completed their change by 10 days, the majority required longer

Morphologic alterations in the rat medullary collecting duct following potassium depletion

Morphologic alterations in the rat medullary collecting duct following potassium depletion. Freeze-fracture and thin-section electron microscopy and morphometry were used to characterize further the response of the rat medullary collecting duct to potassium depletion. In freeze-fracture replicas, principal cells and intercalated cells were identified based on the assumption that intercalated cells possess a high density of rod-shaped intra-membrane particles in their luminal membranes. Potassium depletion caused an increase in the relative number of cells with a high density of rod-shaped particles from the control level of 22% to 31% after 2 weeks and to 36% after 4 weeks. The frequency of intercalated cells identified by thin-section criteria was, however, about 35% in controls and unchanged by potassium depletion. This suggests that intercalated cells can have two types of membrane morphology. In potassium depletion, all intercalated cells display a high density of rod-shaped particles in their luminal membranes. In addition, the luminal membrane area of intercalated cells increased more than threefold, and the density of their rod-shaped particles increased by 21%. These observations suggest that the intercalated cell and its rod-shaped particle may be involved with the potassium reabsorption that occurs in this nephron segment with potassium depletion.Modifications morphologiques du canal collecteur du rat consécutives à une depletion en potassium. Le cryo-décapage, la microscopie électronique sur coupes fines et la morphométrie ont été utilisés pour mieux établir la réponse du canal collecteur médullaire du rat à la depletion en potassium. Sur les répliques de cryo-décapage les cellules principales et les cellules intercalaires ont été identifiées à partir de l'hypothèse selon laquelle les cellules intercalaires possèdent une grande densité de particules intra-membranaires luminales en forme de batonnets. La depletion en potassium a déterminé une augmentation du nombre relatif de cellules de ce type de 22% chez les témoins à 33% après 2 semaines et 36% après 4 semaines. La fréquence des cellules intercalaires identifiées sur coupes minces, cependant, était de 35% chez les contrôles et non modifiés par la depletion en potassium. Cela suggère que les cellules intercalaires peuvent avoir deux types de morphologies membranaires. Dans la depletion en potassium toutes les cellules intercalaires ont une grande densité de particules en forme de batonnets dans leurs membranes luminales. De plus, la surface membranaire luminale des cellules intercalaires augmente de plus de trois fois et la densité des particules augmente de 21%. Ces observations suggèrent que les cellules intercalaires et leurs particules en forme de batonnets peuvent être impliquées dans la réabsorption de potassium qui prend place dans ce segment du néphron au cours de la déplétion en potassium