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At least 19 recordsLinked to original sources
PubMed1992

Dynamics of TGF-initiated nephron-nephron interactions in normotensive rats and SHR.

Proximal tubular pressure, glomerular filtration rate, and early distal tubule Cl- oscillate at 35 mHz in normotensive rats because of tubuloglomerular feedback (TGF); the oscillation bifurcates to chaos in spontaneously hypertensive rats (SHR). To examine the importance of TGF-initiated vascular interactions between nephrons in these dynamics, we measured tubular pressure simultaneously in two or more nephrons. The oscillations were synchronized in nephrons supplied by a common cortical radial artery. The correlation coefficient of pressure records from coupled nephrons was 0.86 +/- 0.02. Intratubular furosemide perfusion diminished the oscillation in both the perfused and the coupled nephron; total autospectral power in each of the nephrons and cross-spectral power were reduced to 45% of control. The correlation between noncoupled nephrons was not significant, and intratubular furosemide perfused in one nephron had no effect on adjacent but noncoupled nephrons. In SHR, the correlation coefficient of tubular pressure records was high from coupled nephrons only; furosemide diminished the autospectral power of pressure fluctuations to approximately 60-75% of control in both perfused and coupled nephrons, and cross-spectral power was affected by a similar amount. Nephron-nephron interactions, specific to vascular connectivity, persist in SHR and appear to be stronger than in normotensive rats.

Animals↗
PubMed1995

Magnitude of TGF-initiated nephron-nephron interactions is increased in SHR.

We compared the tubuloglomerular feedback (TGF)-initiated nephron-nephron interaction in spontaneously hypertensive rats (SHR) and normotensive Sprague-Dawley (SD) rats. Interaction strength was assessed by measuring stop-flow pressure (delta SFP) responses in pairs of nephrons, where only one nephron of the pair was microperfused. The vascular connection was determined from casts of the nephrons and vessels; length of arteriolar separation between the two glomeruli was measured on the casts. When microperfusion rate was increased from 5 to 50 nl/min, delta SFP in perfused nephrons was 10.6 +/- 0.6 and 10.2 +/- 0.7 mmHg [not significant (NS)] in SD and SHR, respectively. In the matched unperfused nephrons from the same cortical radial artery, delta SFP was 1.3 +/- 0.2 and 2.9 +/- 0.7 mmHg (P < 0.05) in SD and SHR. When the perfused and unperfused nephron originated from different cortical radial arteries, delta SFP in the unperfused nephrons was -0.1 +/- 0.2 and 0.0 +/- 0.3 mmHg (NS) in SD and SHR, respectively. In both strains, interaction strength varied inversely with glomerular separation. When the dependence on distance was taken into account, interaction strength was about threefold greater in SHR than in SD. We conclude that the nephron-nephron interaction is significantly greater in SHR. The dependence of interaction strength on distance separating the glomeruli suggests that the interaction is propagated along the preglomerular vasculature.

Animals↗
PubMed1991

Developing nephrons in adolescent dogfish, Scyliorhinus caniculus (L.), with reference to ultrastructure of early stages, histogenesis of the renal countercurrent system, and nephron segmentation in marine elasmobranchs.

Light and electron microscopy of the excretory kidney of adolescent dogfish, Scyliorhinus caniculus (L.), revealed immature and mature nephrons as well as four developmental stages of nephrons. At stage I the nephron was characterized by a condensed mass of mesenchymal cells in the center of several concentric layers of connective tissue. At stage II of the nephron, the S-shaped body was an elongate cyst with a high prismatic epithelium that was connected by a developing collecting tubule with the collecting duct system. At stage III, the developing nephrons already possess the essential features of the mature nephron but lack complete differentiation. Developing renal corpuscles had one afferent arteriole and two efferent vessels. Developing tubules ran four times between the lateral bundle zone and the mesial tissue zone before they joined the collecting duct system. A continuous sheath of flat cells, encompassing the collecting duct system, extended around the developing lateral bundle. A rudimentary central vessel ran from the developing lateral bundle to the venous sinusoid capillaries between the mesial convolutions. Developmental stage IV was similar to the mature nephron, however, renal corpuscles and tubular segments were smaller than those of mature nephrons. Conclusive evidence for morphological homology of elasmobranch nephron segments and collecting tubule-collecting duct system with those of other vertebrates is provided. The origin and nature of the central vessel and the bundle sheath is clarified. These specific structures of marine elasmobranch kidney supposedly are of great functional relevance for the renal countercurrent system that in turn is essential for ion- and osmo-regulation.

Animals↗
PubMed1992

[Usefulness of microdissection of nephron segments and fluorescent indicator for molecular biological studies of nephron functions].

The kidney consists of numerous functional units called nephrons. Thus, the use of individual nephron segments is essential to characterize their functional properties and to clarify the molecular basis of site-specific functions. Nephron segments can be microdissected from collagenase-treated renal slices under a stereomicroscope. A variety of intracellular ionic concentrations or membrane potential can be determined with various fluorescent probes. Fura-2/AM-loaded nephron segments reveal a transient increase of cytosolic free calcium concentrations by agonists such as angiotensin II, vasopressin, kinins, etc. To localize their receptors or to characterize their subtypes, this technique is especially beneficial, because tiny fragments of the nephron are sufficient by combination with a two-wave length microscope fluorometer. As an example, discovery of a novel vasopressin receptor (Vp) is described.

Angiotensin II↗
PubMed1979

Primary culture of mammalian nephron epithelia: requirements for cell outgrowth and proliferation from defined explanted nephron segments.

Nephron segments were dissected from fetal or from early postnatal rabbit kidneys (n = 86) and explanted individually into primary tissue culture. Outgrowth of epithelioid cells and proliferation in monolayers from the collecting tubule and the thick ascending limb of Henle's loop occurred regularly if a special substratum and matrix were used. Media were either supplemented with non-proteins (defined media) or with embryo extract and fetal sera (undefined media). Outgrowth and monolayer spreading were recorded by Differential Interference Contrast Microscopy. Monolayer cells resemble those seen with the same recording technique during tubule in vitro perfusion. Undefined media were essential for growth of convoluted tubule segments from embryonic Nephron Anlagen and outgrowth of cells from proximal straight tubules, in contrast to the distal nephron segments. The specific functional and morphological properties of cells derived from primary culture of nephron segments are under study.

Animals↗
PubMed1976

Effect of diuresis and nephron dimensional heterogeneity on the distribution of nephron filtration rates.

Conflicting data in studies of the effect of natriuresis on intrarenal single nephron glomerular filtration rate (SNGFR) redistribution may arise from the interplay of hitherto largely overlooked factors. In the present work, the effect of diuresis induced by saline, glucose or mannitol, as well as the effect of anatomical nephron heterogeneity, were studied. A highly significant positive correlation was found between the logarithm of the urine flow per gram of kidney weight (log V) and the mean superficial (S) to mean juxtamedullary (JM) SNGFR ratio. The rise in S/JM SNGFR with diuresis was primarily a function of decreased JM SNGFR. Total proximal tubular length (TPL) was used as a measure of nephron size. The distribution of nephron sizes was evaluated as S/JM TPL. The effects of urine flow and anatomical heterogeneity on S/JM SNGFR were spearated by means of multiple regression analysis, which yielded the following equation: S/JM SNGFR = -0.049 + 0.179 log V + 0.818 S/JM TPL. Both slopes were highly significant (P less than 0.001). These findings indicate that S/JM SNGFR increases with urine flow, independently of sodium homeostasis, and that anatomical heterogeneity has a marked effect and must, therefore, be controlled. Conflicting data in the literature are harmonized with the present data when appropriate correction can be made for the dimensional factor. There is no evidence that SNGFR redistributions play a role in sodium homeostasis.

Animals↗
PubMed1977

Developmental changes in nephron number, proximal tubular length and superficial nephron glomerular filtration rate of rats.

1. Post-natal development of single nephron glomerular filtration rate, superficial proximal tubular length, nephron number and kidney weight have been studied in Sprague Dawley and in Wistar rats. 2. Superficial tubular length is a non-linear function of body weight or age. There seems to be a rapid growth until animals weigh about 150 g in Wistar rats. In this strain, growth is slower thereafter. This difference is not as evident in Sprague Dawley rats. 3. Nephron numbers increase over the same period at which rapid tubular growth occurs. 4. Sprague Dawley rats have somewhat fewer, but longer, proximal tubules than do Wistar rats. 5. In all animals weighing more than 100 g, SNGFR is linearly related to weight. For younger, smaller Sprague Dawley rats, the same linearity holds over the age range studied--older than 20 days of age. In Wistar rats, SNGFR relative to weight is less in young animals. 6. By relating SNGFR to total kidney GFR, evidence is obtained that maturation of renal function also involves a greater increase in filtration by superficial than by juxtamedullary nephrons.

Age Factors↗
PubMed1998

Detailed mapping of ochratoxin A reabsorption along the rat nephron in vivo: the nephrotoxin can be reabsorbed in all nephron segments by different mechanisms.

Ochratoxin A (OTA) is a widespread nephrotoxin excreted to a substantial degree via the kidney. Previously we showed that [3H]OTA can be reabsorbed along the rat nephron in vivo (Zingerle et al., 1997). In this study we investigated in detail the contribution of different nephron segments to [3H]OTA reabsorption and determined the possible mechanisms involved by microinfusion and microperfusion experiments. At pH 6 (approximately 94% of OTA neutral), OTA is reabsorbed in all nephron segments investigated. The estimated fractional reabsorptions (FR) at a tubular load of 20 fmol/min are: proximal convoluted tubule (PCT), 14.8%; proximal straight tubule (PST), 27.4%; ascending limb of Henle's loop (ALH), 13.6%; distal tubule (DT), 11.6%; collecting duct (CD), 24.6%; terminal CD, 22.0%. At pH 8 (approximately 10% of OTA neutral) FR are as follows: PCT, 0%; PST, 25.9%; ALH, 14.0%; DT, 3.2%; CD, 8.2%. Thus, OTA reabsorption in PST and ALH in pH-independent. Reabsorption in PST but not in DT or CD was inhibited by sulfobromophthalein, a substrate of the apical organic anion carrier. L-Phenylalanine did not reduce OTA reabsorption. After intravenous injection of unlabeled OTA, resulting in a plasma concentration of approximately 10(-5) mol/l, the FR of [3H]OTA during early proximal microinfusion was reduced slightly. From our results we conclude: 1) OTA can be reabsorbed in all nephron segments investigated. 2) Under physiological conditions the predominant sites of reabsorption are PST, ALH and terminal CD. 3) Reabsorption in PST and ALH is not pH-dependent. 4) pH-independent reabsorption in PST is mediated by the apical organic anion transporter (OAT-K1), whereas pH-dependent reabsorption in PCT is mediated by H(+)-dipeptide cotransporter(s). 5) Reabsorption also takes place during natural exposure, i.e., when OTA is present in plasma and renal tissue. 6) The high FR in ALH and CD explains, at least in part, the preferential impairment of postproximal functions and the accumulation in renal inner medulla and papila.

Absorption↗
PubMed2001

Synchronization phenomena in nephron-nephron interaction.

Experimental data for tubular pressure oscillations in rat kidneys are analyzed in order to examine the different types of synchronization that can arise between neighboring functional units. For rats with normal blood pressure, the individual unit (the nephron) typically exhibits regular oscillations in its tubular pressure and flow variations. For such rats, both in-phase and antiphase synchronization can be demonstrated in the experimental data. For spontaneously hypertensive rats, where the pressure variations in the individual nephrons are highly irregular, signs of chaotic phase and frequency synchronization can be observed. Accounting for a hemodynamic as well as for a vascular coupling between nephrons that share a common interlobular artery, we develop a mathematical model of the pressure and flow regulation in a pair of adjacent nephrons. We show that this model, for appropriate values of the parameters, can reproduce the different types of experimentally observed synchronization. (c) 2001 American Institute of Physics.

Journal Article↗
PubMed1976

Single nephron glomerular filtration rate ratios of superficial, intercortical and juxtamedullary nephrons in rats during development.

In 20, 40 and 60-day-old rats the filtration rate was studied using Baines modification of Hanssen's Na4Fe (14CN)6 method enabeling the determination of single nephron glomerular filtration rate (SNGFR) ratio between superficial (S), intercortical (I) and juxtamedullary (J) nephrons. The proximal tubule lengths were determined as well. A close correlation was obtained between age and S/I, I/J and S/J of proximal tubule lengths and between age and I/J, S/J 14C-activities of ferro-cyanide. Presented findings confirm the data on the increasing role of superficial nephrons in the course of postnatal development of rat.

Age Factors↗
PubMed2005

The human nephron filter: toward a continuously functioning, implantable artificial nephron system.

BACKGROUND: Nearly 900,000 patients worldwide have end-stage renal disease and require dialysis or kidney transplantation, and this number is expected to more than double by 2010, placing considerable stress on healthcare systems throughout the world. Despite the availability of these forms of renal replacement therapy for nearly four decades, mortality and morbidity is high and patients often have a poor quality of life. METHODS: We have developed a human nephron filter (HNF) utilizing nanotechnology that would eventually make feasible a continuously functioning, implantable artificial kidney. The device consists of two membranes operating in series within one device cartridge. The first membrane mimics the function of the glomerulus, while the second membrane mimics the function of the renal tubules. FINDINGS: The device has been computer-modeled and operating 12 h/day, 7 days/week, the HNF provides the equivalent of 30 ml/min glomerular filtration rate (compared to half that amount for conventional thrice weekly hemodialysis). CONCLUSIONS: The HNF system, by eliminating dialysate and utilizing a novel membrane system created through applied nanotechnology may represent a breakthrough in renal replacement therapy based on the functioning of native kidneys. The enhanced solute removal and wearable design should substantially improve patient outcomes and quality of life.

Computer Simulation↗
PubMed1986

Structural-functional relationships along the distal nephron.

The distal tubule, which includes the thick ascending limb (TAL), the macula densa, and the distal convoluted tubule (DCT), and the collecting duct are structurally heterogeneous, thus reflecting the functional heterogeneity that is also present. As the TAL ascends from medulla to cortex, the surface area of the apical plasma membrane increases while that of the basolateral membrane decreases. The structure of the DCT resembles that of the medullary TAL. An excellent correlation exists between structure, Na-K-ATPase activity, and NaCl reabsorptive capacity in the distal tubule. The collecting duct is subdivided into the initial collecting tubule (ICT), and cortical (CCD), outer medullary (OMCD), and inner medullary (IMCD) collecting ducts. Between the distal tubule and the collecting duct is a transition region termed the connecting segment or connecting tubule (CNT). Considerable structural heterogeneity exists along the collecting duct within the two major cell populations, the intercalated cells and the principal cells. In the CNT, the ICT, and the CCD, potassium loading and mineralocorticoids stimulate Na-K-ATPase activity and cause proliferation of the basolateral membrane of CNT cells and principal cells, thus identifying the cells responsible for mineralocorticoid-stimulated potassium secretion in these regions. Finally, at least two morphologically distinct populations of intercalated cells exist, types A and B. In the rat, type A predominates in the CNT and the OMCD and is believed to be responsible for H+ secretion, at least in the OMCD. Type B predominates in the CCD, where it may be involved in bicarbonate secretion.

Animals↗