The ultrastructure of the nephrons of the desert rodent (Psammomys obesus) kidney II. Thin limbs of henle of long-looped nephrons

Long nephrons are derived from juxtamedullary glomeruli. In their descent through the outer medulla toward the inner medulla, the thin descending limbs (TDLs) of long loops of Henle are consistently excluded from the vascular bundles and occupy the interbundle region. The outer medullary segment of long TDLs (Type II epithelium) is elaborately developed with numerous cellular interdigitations. microvilli, and a cytoplasm well equipped with numerous organelles. The inner medullary segment of these long TDLs is characterized by yet another epithelium that is markedly reduced from its Type II predecessor and is designated as Type III epithelium. It is a very low, flattened epithelium with few cytoplasmic details. In a cross section of the inner medullary TDL, the Type III epithelium appears poorly interdigitated, with only two to four cell processes and their junctional complexes. Shortly before the bend of a long loop of Henle, the epithelium is again altered to one that is well-interdigitated and better equipped with cytoplasmic organelles (Type IV epithelium). It persists through the actual bend of the loop and throughout the entire thin ascending limb (TAL), until the latter's transition to the distal tubule at the level of the inner/outer medullary border. We conclude that the Type II epithelium of the outer medullary segments of long TDLs in Psammomys is suitably constructed for involvement in energized transport of solutes. The possibility for a similar role in the Type IV epithelium of the bends and TALs is not excluded by our data. However, the Type III epithelium of the inner medullary segments of long TDLs is most suitably constructed for the concentration of its luminal fluids via water extraction. A comparison between these epithelial types and their permeabilities in various species is presented.     

小鼠短髓襻肾单位在外髓的分布

目的 肾外髓间质渗透梯度形成的机制与髓襻上皮转运功能及其毗邻关系有密切关系,本研究拟建立短髓袢肾单位在外髓的走行规律。方法C57/BL/6J小鼠3只,灌流固定后取肾组织块并树脂812包埋,垂直肾长轴连续半薄切片,从肾被膜到内外髓交界处,共得到1 200张2.5μm厚的连续切片,显微镜下获取数字图像,计算机配准,C语言编程,进而追踪来自皮质浅层和中层的120个短髓襻肾单位。结果 短髓襻肾单位的53%起于肾皮质外1/3,47%起于中间肾皮质。前者髓襻襻曲分布在外髓内带中部同一水平,其襻曲或完全由细段上皮构成,或由髓襻降支细段上皮与升支粗段上皮移行构成;来自中间皮质的短髓襻襻曲位于外髓内带内侧1/2的不同水平,其深度与其肾小球在中间皮质的深度成正比。其襻曲由髓襻升支粗段上皮构成,并在襻曲前构成约50~450μm长的髓襻降支。最深的襻曲在外髓内带弯曲走行。结论髓袢襻曲在外髓的位置及上皮类型不同,提示外髓不同区域的小管对超滤液重吸收的成分也有所区别,对外髓深部渗透梯度增高的形成产生一定的影响;而襻曲的位置和上皮构成与肾小球在皮质的位置相关,提示肾小球的滤过与肾小管的重吸收功能有整体的调节。     

小鼠长髓襻肾单位在髓质的分布

目的 肾髓质渗透梯度的形成与髓襻走行及转运功能关系密切,本研究拟建立长髓袢肾单位在髓质的走行规律。方法C57BL6/J小鼠3只,灌流固定后取肾组织块,树脂812包埋,垂直肾长轴连续半薄切片,从肾被膜到内髓,共得到2 000张2.5μm厚的连续切片,显微镜下获取数字图像,计算机配准,C语言编程,进而追踪26条长髓襻肾单位。结果 长髓襻肾单位来自中层和近髓质区的皮质,其髓襻襻曲分布在内髓不同水平,最深的可达肾乳头。通过数字追踪发现,在外髓内带外侧区,髓襻降支细段起始部高度盘曲走行,其盘曲部分的长度是其直线距离的2倍。在盘曲走行中,与同源的髓襻升支粗段间隔排列。最长的长髓襻升支粗段走行在外髓内带的血管丛。在外髓内带的内侧区,髓襻降支细段与髓襻升支粗段紧密相邻,直行进入内髓。结论 降支细段在外髓内带高度盘曲走行,在增加了这一节段长度的同时,也增加了这一节段的转运功能,提示此结构特征对该区域的渗透梯度形成可能产生重要影响。     

The ultrastructure of the thin limbs of henle in kidneys of the desert heteromyid (Perognathus penicillatus)

The thin limbs of both long- and short-looped nephrons in Perognathus kidneys were studied with transmission and scanning electron microscopy. The superficial nephrons have a short thin limb located in the vascular bundles of the outer medulla and are characterized by a simple, low-lying epithelium (0.4 ± 0.1 μ thickness). In contrast, the first descending part of the thin limb of the majority of midcortical and juxtamedullary nephrons has a relatively thick epithelium (1.7 ± 0.6 μ in thickness) with marked lateral and basal interdigitation and a dense surface covering of microvilli. The remaining part of the long descending thin limb is relatively simple with a low-lying epithelium (0.6 ± 0.1 μ in thickness), decorated on its surface by sparse microplicae. The bend of the loop and the ascending limb are covered by a very simple low-lying epithelium (0.6 ± 0.2 μ in thickness) with relatively little surface modification. The extreme urine-concentrating ability of Perognathus does not appear to be due to the development of a unique thin loop epithelium but rather to the extensive length of the inner and outer medulla.     

Effect of increased distal sodium delivery on organic osmolytes and cell electrolytes in the renal outer medulla

Sodium absorption in distal tubule segments was stimulated by increasing the distal delivery via infusion of hypertonic saline. In these animals, and in control rats, electrolyte concentrations in thick ascending limb cells, light and dark cells of the collecting duct in the outer and inner stripe of the outer medulla and in cells of the proximal straight tubule (outer stripe only) were studied. The measurements were performed by electron microprobe analysis of freeze-dried cryosections of the outer medulla. In addition, organic osmolytes (glycerophosphorylcholine, betaine and myo-inositol) were measured by high performance liquid chromatography in cortex and outer medulla. Augmented delivery of sodium chloride to the distal tubule was associated with increased sodium concentrations of thick ascending limb cells both in the outer and inner stripe and of medullary collecting duct light and dark cells in the outer stripe. While the sum of organic osmolyte concentrations was 28% higher in the outer medulla of the salt-loaded animals compared with controls, this value was unchanged in the renal cortex. These findings indicate that the primary event underlying stimulation of sodium absorption along the thick ascending limb during increased distal sodium delivery is enhanced entry of sodium across the apical cell membrane. This would be expected to lead to higher cell sodium concentrations and stimulation of basolateral active Na-K-exchange. The enhanced transport activity of outer medullary tubules may be associated with increased interstitial tonicities and intracellular retention of organic osmolytes.     

Urea handling by the renal countercurrent system: Insights from computer simulation

Summary The renal handling of urea has been investigated with the aid of a computer model of the countercurrent system in which active electrolyte reabsorption occurs along the entire ascending limb of Henle's loop. In this model, summarized in Fig. 9, the buildup of a corticopapillary gradient for urea is optimized if there isnet addition of urea to loops of Henle only in the outer medulla. This added urea remains within the tubular system until it is reabsorbed from collecting ducts in the inner medulla. Thus, a net transfer of urea from outer to inner medulla is accomplished (via distal tubule and cortical collecting duct). There is nonet addition of urea to loops of Henle within the inner medulla; in this region, the loops act simply as countercurrent exchangers for urea. Computer simulation of systematic variation in the urea permeabilities of each nephron segment shows that interference with any element of the above schema results in impairment of the medullary accumulation of urea relative to plasma. Simulation of varying rates of urinary urea excretion demonstrates that this model can account for the ability of the kidney to excrete substantial amounts of urea without an accompanying osmotic loss of water. The major insight gained from this study is that net addition of urea to loops of Henle in the outer medulla greatly enhances the medullary accumulation of urea, whereas, net addition of urea to loops within the inner medulla tends to defeat such accumulation and hence the urinary concentrating process. This general principle applies also to an alternate model of the countercurrent system, in which electrolyte reabsorption from thin ascending limbs of Henle is passive.     

小鼠肾近端小管的三维重建

目的 研究小鼠肾近端小管三维空间走行的特点及规律。 方法 C57/BL/6J小鼠3只,灌流固定后取肾组织块并树脂812包埋,垂直肾长轴连续半薄切片,从肾被膜到肾外髓外带共得到1 200张2.5μm厚的连续切片,显微镜下获取数字图像,计算机配准,C语言编程,追踪并三维重建58条近端小管走行。 结果 在皮质迷路中,近端小管起始段在离开肾小球后,均先向被膜方向走行约100～1 400μm后返折,在各自肾小球周围盘曲并占据相对独立的区域,很少和其他肾单位近端小管曲部区域重合。浅表皮质肾单位与中间皮质肾单位的近曲小管盘曲紧密,所占空间比近髓肾单位近曲小管小。在髓放线中,近端小管直部的走行有明显的层次：来源于浅表皮质肾单位的近端小管直部走行于中央,来源于皮质深部肾单位的近直小管则依次走行在其外围,皮质最深层的肾单位的近直小管几乎无直部。所有近端小管均止于肾外髓外带与内带的交界处,并移行为髓袢降支细段。 结论 小鼠近端小管的起始段、曲部和直部在皮质迷路与髓放线都有各自走行区间,其吡邻关系及所处生物学环境不同,这对肾近端小管不同节段对不同物质转运功能的生理及病理评估提供形态依据。     

Acute kidney injury in human leptospirosis: an immunohistochemical study with pathophysiological correlation

Tubulointerstitial nephritis is a common clinicopathological finding in leptospirosis. Clinically, nonoliguric acute kidney injury (AKI), hypokalemia, sodium, and magnesium wasting frequently occur in leptospirosis. The exact mechanisms of renal involvement remain largely unclear. Immunohistochemistry to detect expression of the endogenous sodium/hydrogen exchanger isoform 3 (NHE 3), aquaporin 1 and 2, α-Na⁺K⁺ATPase, and sodium–potassium–chloride cotransporter in its NKCC2 isoform was performed on kidneys removed during autopsy of human leptospirosis cases and kidneys removed during autopsy of human non-leptospirosis cases with and without evidence of acute tubular necrosis (ATN). A decrease in NHE 3, aquaporin 1, and α-Na⁺K⁺ATPase expression occurred in proximal convoluted tubule cells. Expression of aquaporin 1 was preserved along the descending thin limb of the loop of Henle in the outer medulla. α-Na⁺K⁺ATpase expression was essentially preserved in the distal tubules, i.e., the thick ascending limb of the loop of Henle, macula densa, and distal convoluted tubule. Aquaporin 2 expression in the collecting tubules was enhanced compared to those of non-leptospirotic kidneys. NKCC2 cotransport isoform was expressed in the thick ascending limb of the loop of Henle and was essentially preserved in leptospirotic kidneys. Primary injury of the proximal convoluted tubules is regarded as the hallmark of the kidney in leptospirosis. Sodium and water transport are particularly affected with increased distal potassium excretion, hypokalemia, and polyuria. Enhanced expression of aquaporin 2 in medullary collecting tubules is probably an attempt to retain water during the nonoliguric phase of renal failure.     

Distribution of vasoactive intestinal peptide-sensitive adenylate cyclase activity along the rabbit nephron

The effect of vasoactive intestinal peptide (VIP) upon adenylate cyclase (AC) activity has been determined in defined microdissected renal tubules isolated from collagenase-treated rabbit kidneys. In the presence of 10 M GTP, 1 M VIP gave marked stimulations of AC over basal values in the bright portion of the distal convoluted tubule (DCTb) (10.1-fold), and in the collecting tubule isolated from the inner stripe of the outer medulla (OMCTi, 7.8-fold). Less pronounced effects of VIP were found in the medullary collecting tubule isolated from the outer stripe (2.5-fold) and in the granular portion of the distal convoluted tubule (2.0-fold). VIP stimulation of AC activity in these segments amounted to 25 to 40% of the effect elicited by other agonists (arginine vasopressin, calcitonin or parathyroid hormone) in their respective target segments. A low response to VIP was observed in the cortical thick ascending limb (1.8-fold) which represented less than 5% of the calcitonin-stimulated AC activity. In the thin descending limb VIP produced a slight and variable stimulation of AC. VIP was without effect upon AC in the convoluted and straight portions of the proximal tubule, the medullary thick ascending limb and the cortical collecting tubule. Halfmaximal stimulation of AC by VIP was observed at 26±10 nM (n=3) in OMCTi and at 19 nM (n=2) in DCTb. Related peptides glucagon, secretin and PHI gave lower stimulations of AC compared to VIP in OMCTi. Conversely for rat OMCTi, under identical conditions, glucagon was much more effective than VIP.     

Physical properties of isolated perfused basement membranes from rabbit loop of Henle

Isolated, perfused segments of late proximal straight tubule, descending thin limb of Henle, and ascending thick limb of Henle from the rabbit were studied before and after removal of the epithelium with sodium deoxycholate. The relationship between transmural hydrostatic pressure and outer tubule diameter was similar in paired intact tubules and basement membranes, indicating that basement membrane is the principal determinent of tubule distensibility. As calculated from teh measured perfusate flow at several different transmembrane hydrostatic pressures, the hydraulic conductivity of the basement membranes was 6-8 X 10(-3) cm3/cm2.min.cmH2O. With use of these LP values and the calculated oncotic pressure required experimentally to reduce transmembrane hydrostatic pressure transiently to zero, the apparent reflection coefficient of the basement membranes for serum albumin was estimated to be 0.05-0.16. It is concluded that basement membranes of the loop and of other previously studied segments of rabbit nephron provide very strong and elastic mechanical support to the epithelium while having minimal resistance to flow of water and of solutes as large as serum albumin.     

Ultrastructure of the thick ascending limb of henle in the rat kidney

The thick ascending limb of Henle (TAL) in the rat until recently has been considered a morphologically homogeneous structure despite physiologic and biochemical evidence to the contrary. The present study was designed to examine the ultrastructural characteristics of the TAL in the inner cortex and the outer and inner stripes of the outer medulla using qualitative and quantitative transmission electron microscopy. Kidneys of male Sprague-Dawley rats were preserved by in vivo perfusion with glutaraldehyde for light and electron microscopy. The peritubular diameter and cell height were determined by direct measurements on tubule cross sections. Morphometric analyses were performed on montages of tubule cross sections. The peritubular diameter of the TAl was similar in the three regions under investigation, but the TAL cells were taller in the inner stripe than in the inner cortex and outer stripe. Morphometry revealed significant differences between the three regions with respect to the mean tubular cross-sectional area (A_T), the surface density (S_V), and the surface area per mm of tubule (S_T) of apical and basolateral plasma membranes, and the volume density (V_V) of mitochondria. The major morphologic division appeared to be between the inner stripe segment and the remainder of the TAL. These findings document the presence of significant morphologic heterogeneity of the rat TAL.     

Immunofluorescent localization of Tamm-Horsfall mucoprotein in human kidney

A fluorescein-labelled antiserum to human Tamm-Horsfall mucoprotein applied to frozen human kidney sections gave strong specific labelling, mainly of cells of tubules in the outer medulla. By comparison with adjacent serial sections stained for alkaline phosphatase and succinic dehydrogenase, it is suggested that material reacting immunologically as Tamm-Horsfall muco-protein is found particularly in the cells of the ascending limb of the loop of Henle and the macula densa segment of the distal tubule.     

Micropuncture study of water and electrolyte movements along the loop of henle in Psammomys with special reference to magnesium,calcium and phosphorus

Summary Cortical and papillary micropuncture experiments were carried out on Psammomys undergoing mild hypertonic salt diuresis. Tubular fluid was collected along the proximal tubule or at the early distal tubule level, and at the tip of the longest Henle loop.³H-inulin, Na, K, Cl, Mg, Ca and P concentrations, as well as osmotic pressure, were determined in all samples. The results indicate a) no large net water movement along the loop; b) substantial addition of Na, K, Cl, Mg, and to a lesser extent Ca, along the descending limb, in proportion to the gradient; c) the tubular flow rate of phosphorus remains constant at the tip of the loop irrespective of the gradient. The constancy of the load of Na, K, Cl, Mg and Ca delivered to the distal superficial nephron, irrespective of the urinary osmotic pressure, indicates that medullary recycling between the ascending and descending limbs exists for Mg, Cl, and Ca, and confirms its existence for Na and K. In contrast, phosphorus behaves like inulin along the descending limb. A general conclusion is that in Psammomys the concentrating process along the descending limb of Henle results mainly from net addition of solutes, and not from water withdrawal.Part of this work was presented at the 5th Congress of Nephrology, Mexico 1972.     

Morphologic and functional evidence for oxygen deficiency in the isolated perfused rat kidney

Morphologic and functional studies were undertaken in the isolated rat kidney, perfused with an albumin-Krebs-Henseleit solution, to which 5% human erythrocytes and/or various amino acids had been added. Perfused only with the albumin-Krebs-Henseleit solution, the kidneys displayed a characteristic pattern of cell necrosis after 2 hours of perfusion, which was confined to the interbundle region of the outer medulla and was not evident in either the cortex or the inner medulla. In the outer stripe only those proximal straight tubules (P3 segments) farthest from the vascular bundles were damaged. In the inner stripe only those thick ascending loops of Henle at the periphery of the vascular bundles escaped damage; all thick ascending loops of Henle lying farthest from the bundles were severely damaged. The number of damaged tubules increased toward the border to the inner medulla. Necroses in both segments, P3 and thick ascending loops of Henle, could be prevented by perfusion with the erythrocyte-albumin-Krebs-Henseleit solution but not by the addition of glutathione, in the absence of erythrocytes. Perfusion with the erythrocyte medium also significantly improved glomerular filtration rate and sodium and glucose reabsorption. It is concluded that, in the isolated, erythrocyte-free perfused kidney, the oxygen content of the "arterial" vasa recta in the vascular bundles is only sufficient to supply the tubules in the immediate surroundings. Countercurrent exchange in the vascular bundles between arterial and "venous" vasa recta progressively lowers the arterial oxygen content as the inner stripe of the outer medulla is approached and with it the number of tubules receiving an adequate oxygen supply.     

The position of short and long loops of Henle in the rat kidney

Summary To determine the histotopographical relations of short and long loops of Henle in the rat kidney single short and long-looped nephrons were marked by microinjection with a silicone rubber and subsequently traced in histological serial sections. Short loops of Henle, derived from both supericial and midcortical nephrons, follow a similar course and possess similar histotopographical relations. In the medullary rays of the renal cortex and in the outer stripe of the outer medullary zone both limbs of short loops of Henle are lying together, near to the corresponding collecting duct. At the transition of outer and inner stripes the descending limbs turn towards the bundles and descend in the bundle periphery juxtaposed to venous vasa recta. After looping back at the junction of outer and inner zones they change position and ascend distant from the bundles in the vicinity of collecting ducts.The straight proximal portions of long-looped nephrons directly penetrate the outer stripe transversing this zone in tortuous course. In the inner stripe, the thin descending limbs of long loops of Henle descend distant from the bundles among the ascending thick limbs. In the inner medullary zone, neither the descending nor the ascending thin limbs have an exactly defined constant histotopographical position. The long loops ascend straight through the outer medullary zone, usually near to a vascular bundle, and reach the convoluted portion without transversing the medullary rays.The regularity of the histological pattern in the outer medullary zone suggests that the arrangement of the loops may influence their function, whereas in the inner zone the histotopographical position of the loop limbs does not appear to be a functionally important parameter.

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Zusammenfassung Um die histotopographischen Beziehungen von kurzen und langen Henleschen Schleifen in der Rattenniere zu bestimmen, wurden einzelne Nephrone durch Injektion mit einem Kunststoff gekennzeichnet und ihr Verlauf in histologischen Serienschnitten verfolgt.Die kurzen Henleschen Schleifen der Rattenniere gehören zu den oberflächlichen und intermediären Nephronen; sie alle haben einen sehr ähnlichen Verlauf. In den Markstrahlen der Nierenrinde und im Außenstreifen des Nierenmarkes liegen die zusammengehörenden Schenkel einer Schleife nebeneinander und gleichzeitig in der Nähe des zugehörigen Sammelrohres. An der Grenze zum Innenstreifen biegen die absteigenden Schleifenschenkel zu einem Gefäßbündel hin, in dessen Peripherie sie absteigen — eng assoziiert mit aufsteigenden venösen Vasa recta. Am Ende des Innenstreifens biegen sie um; ihre aufsteigenden Schenkel verlaufen in der Nähe von Sammelrohren.Die langen Henleschen Schleifen gehören zu den juxtamedullären Nephronen. Im Gegensatz zu den geraden Anteilen des distalen Tubulus verlaufen die geraden Anteile des proximalen Tubulus der langen Schleifen im Außenstreifen gewunden. Im Innenstreifen verlaufen ihre absteigenden Schleifenschenkel abseits der Gefäßbündel zwischen aufsteigenden Schleifenschenkeln, während ihre aufsteigenden Schenkel häufig in der Nähe eines Gefäßbündels liegen. In der Innenzone haben weder die absteigenden noch die aufsteigenden Schleifenschenkel charakteristische histotopographische Beziehungen.Die strenge Ordnung der Strukturen im Innenstreifen der Rattenniere läßt vermuten, daß hier die Lagebeziehungen der Henleschen Schleifen für ihre Funktion von Bedeutung sind, während in der Innenzone die genaue Zuordnung der Schleifenschenkel zu anderen Strukturen für funktionell wenig bedutend erachtet wird.

     

Glucagon receptors along the nephron: [125I]glucagon binding in rat tubules

Binding of [¹²⁵I]glucagon was measured in microdissected pieces of tubules from the rat nephron. Specific glucagon binding sites were found only in nephron segments containing a glucagon-sensititive adenylate cyclase activity. At 7.5 nM labelled hormone, higher levels of specific binding (16–27×10^–18 mol mm^–1) were found in the thick ascending limb of the Henle's loop and in the distal convoluted tubule and lower binding levels (2–5×10^–18 mol mm^–) in the collecting tubule whereas specific binding could not be detected in the proximal tubule and in the thin segments of the Henle's loop. In the medullary thick ascending limb, Scatchard analysis of specific [¹²⁵I]glucagon binding indicated an apparent equilibrium dissociation constant of 2.4 nM. The stereospecificity of binding sites in medullary thick ascending limbs and medullary collecting tubules, was assessed by competition experiments using unlabelled glucagon, enteroglucagon and unrelated hormones (vasopressin, calcitonin, parathyroid hormone and insulin); in both segments, glucagon was more active than enteroglucagon in displacing labelled glucagon from its tubular binding sites, whereas all other hormones tested were inactive. These results indicate that tubule binding sites might be the physiological receptors for glucagon involved in adenylate cyclase activation.Abbreviations PCT proximal convoluted tubule - TDL thin descending limb - TAL thin ascending limb - MAL medullary thick ascending limb - CAL cortical ascending limb - DCT distal convoluted tubule - CCT cortical collecting tubule - MCT medullary collecting tubule     

The structural organization of the kidney of the desert rodent Psammomys obesus.

The architecture of the desert rodent Psammomys obesus has been studied by means of standard histologic procedures and by single nephron injections. As other rodent kidneys (rat, mouse), the Psammomys kidney consists of two types of nephrons, 66% short looped and 34% long looped nephrons. The cortex is composed of 4 to 5 layers of glomeruli, which lie closely put together, the glomeruli often touch each other. The superficial and the midcortical glomeruli give rise to short looped neophrons, the juxtamedullary to long looped nephrons. In the strongly developed medulla the inner stripe shows the most striking pattern. It consists of two distinct compartments, that of the giant vascular bundles and that of the interbundle regions. The giant vascular bundles consist of about 8 to 14% arterial vasa recta and 39 to 47% venous vasa recta; furthermore they include the thin descending limbs of the short loops of Henle which amount to 44 to 51% of the bundle structures. The tubules of the interbundle regions surround the bundles in a regular pattern. The inner zone is almost completely surrounded by the renal pelvis; the long broad papilla protrudes into the ureter. The thin descending limbs of short looped nephrons traverse the inner stripe inside the giant vascular bundles. Leaving the bundles they turn back within the inner stripe; their ascending limbs lie in the interbundle region. Both limbs of the long loops of Henle run in the interbundle region, together with the ascending limbs of the short loops and the collecting ducts. The long loops penetrate deeply the inner zone. Many bends are found near the tip of the papilla. The renal pelvis has a very specialized form. It penetrates the inner stripe with many complexely shaped extensions, which surround the giant vascular bundles. Large parts of the bundles with their thin walled structures are thus separated from the pelvic urine only by a single layer of cuboidal epithelium. The possible functional importance of the described specializations of the Psammomys kidney (giant vascular bundles, large inner zone, special shape of the renal pelvis) for the urine concentrating and urea recyclng mechanisms is discussed.     

Scanning electron microscopy of basolateral surfaces of rat renal tubules isolated by sequential digestion

Renal tubular cells and segments isolated by a trypsin, pepsin, pronase E digestion procedure were studied with scanning electron microscopy. The basal and lateral surfaces of S1, S2, S3 proximal tubular (PT) segments, descending and ascending thin limbs of Henle (TL), distal ascending thick limb of Henle, or distal straight tubule (DST) and distal convoluted tubule (DCT) segments, connecting tubules (CNT), and collecting ducts (CD) were identified and characterized. The basal processes of the S1 and S2 PT cells were fan shaped, were oriented in a circumferential direction, and terminated in microvilli at the basement membrane. S3 PT cells had microvillous basal processes mainly on the lateral edges of the cells. The basal processes of DST and DCT were similar to PT in orientation but terminated on the basement membrane with flattened, thin attachments. The long-loop descending TL and the ascending TL exhibited distinctive interdigitating cell processes. TL segments with simple contours were present in smaller numbers and were characteristic of short-loop descending limbs. CNT showed some cells with basal surfaces resembling DCT cells and others resembling CD cells. Both cortical and medullary CD segments exhibited intercalated cells with round basal contours and a sparse pattern of basal infolding clefts. The cortical CD principal cells revealed a much more elaborate mosaic of plicae, clefts, and microvilli than those of the medullary CD. These observations extend the previous knowledge gained from transmission electron microscopy and assist in the interpretation of that knowledge.     

Effect of H+ on the membrane potential of silent cells in the ventral and dorsal surface layers of the rat medulla in vitro

In a recent study it was found that in Mg loaded rats, the fraction of filtered Mg (% E Mg) recovered in the bend of the loop of Henle of papilla was greater than the filtered load. However, the site of this Mg addition was unspecified and could be either the juxtamedullary proximal tubule, the pars recta, or in the papilla, the descending limb of the loop of Henle.In order to investigate the movement of Mg in the various structures of the papilla, we have studied: 1. The transport of this electrolyte along the collecting duct. 2. Its relative concentration in the loop of Henle and in the adjacent vasa recta. The experiments have been performed in hydropenic and Mg loaded rats.In the collecting duct, the inulin and Mg concentrations increase proportionally, indicating an absence of any transport of Mg along this part of this nephron.In the vasa recta of the accessible papilla, the capillary over peripheral plasma Mg ratio (C/UF Mg) in hydropenia and after Mg loading [1.88±0.15 (ES) and 2.89±0.24] were significantly lower than the corresponding TF/UF Mg in the adjacent loops of Henle (2.90±0.17 and 4.04±0.37). This finding reduces the possibilities of a Mg passive diffusion from the capillaries to the tubular lumen, unless the electrical potential of the descending limb is more negative than –5 mV. The hypothesis of an active secretion, or a passive diffusion of Mg in the deep proximal tubule, in the pars recta, or in the early non accessible descending limb constitutes the other alternative.This work was partially supported by the Medical Research Council of Canada, grant MA 4472, by special funds from the University of Montreal, and by NIH grant 1 R01 AM 20136-01     

Effect of water intake on Na−K-ATPase in nephron segments of the desert rodent,Jaculus orientalis

Na–K-ATPase activity was measured in individual pieces of nephron microdissected from collagenase-treated kidneys of jerboas,Jaculus orientalis. Na–K-ATPase activity was high in the distal convoluted tubule, intermediate in the thick ascending limb of the loop of Henle and low in the proximal and collecting tubule. When jerboas were adapted for several weeks to a hydrated diet and excreted a more diluted urine, Na–K-ATPase activity was altered in specific segments of the nephron: 1. In the proximal convoluted tubule, Na–K-ATPase activity decreased, especially in the juxtamedullary nephrons, suggesting that internephron heterogeneity was diminished; 2. In the medullary thick ascending limb, but not in the cortical portion, Na–K-ATPase activity decreased by 30%; 3. Na–K-ATPase was also diminished in the cortical collecting tubules (by 20%) but not in the medullary collecting tubule. Morphometric measurements also indicate that changes in Na–K-ATPase activity observed in the thick ascending limb are correlated to a cell atrophy, whereas in the collecting tubule, they occur independently of any visible morphological alteration. These differences in Na–K-ATPase activity are likely to be secondary to the changes in the plasma concentration of vasopressin previously described during such adaptation and to be involved in the control of water and sodium handling.