Phenomenological model relating cell shape to water reabsorption in proximal nephron

1978 ◽  
Vol 234 (4) ◽  
pp. F308-F317 ◽  
Author(s):  
D. J. Welling ◽  
L. W. Welling ◽  
J. J. Hill
Keyword(s):  
Proximal Tubule ◽  
Phenomenological Model ◽  
Cell Shape ◽  
Serum Proteins ◽  
Water Movement ◽  
Diffusion Constant ◽  
Simple Relationship ◽  
Protein Diffusion ◽  
Flow Parameters ◽  
Morphologic Data

If the complex pattern of intercellular channels in proximal tubule is determined in part by the forces of large transepithelial water flow, the shape of the cells is an indicator of the type and magnitude of the forces required for water movement and the routes of that flow. To test this thesis, morphologic data and volume flow parameters for rabbit proximal tubule are related generally by a mass balance equation. If the intercellular boundaries are assumed to be highly deformable and to respond to changes in hydrostatic pressure, the solution to that equation is a simple relationship between cell shape and the forces required for water movement. The resulting phenomenological model suggests an important new role for peritubular serum proteins and can be used to compute reasonable values for cell wall hydraulic conductivity, intercellular protein diffusion constant, and a channel fluid osmolality not more than 1% greater than that of luminal fluid. It is concluded that quantitative morphologic studies may serve as a powerful means for evaluating and understanding transport phenomena in the nephron.

Developmental changes in rabbit juxtamedullary proximal convoluted tubule water permeability

1996 ◽  
Vol 271 (4) ◽  
pp. F871-F876 ◽  
Author(s):  
R. Quigley ◽  
M. Baum
Keyword(s):  
Proximal Tubule ◽  
Water Transport ◽  
Water Permeability ◽  
Water Movement ◽  
Adult Rabbit ◽  
Osmotic Water ◽  
Glomerular Filtrate ◽  
Convoluted Tubules ◽  
Insight Into

The mammalian proximal tubule reabsorbs the bulk of the glomerular filtrate in a nearly isosmotic fashion due to the high osmotic water permeability (Pf) of this segment. Although the characteristics of proximal tubule water transport have been studied in the adult proximal tubule, little is known about the neonatal segment. The present study directly measured the Pf and diffusional water permeability (PDW) of neonatal (10 +/- 2 day old) and adult rabbit juxtamedullary proximal convoluted tubules (PCT) using in vitro microperfusion. The Pf of neonatal juxtamedullary PCT was greater than the Pf of adult juxtamedullary PCT. In contrast, the PDW was not different between the two groups. The Pf and PDW values of both neonatal and adult tubules were inhibited to the same degree by p-chloromercuribenzene sulfonate and had identical activation energies. The transepithelial reflection coefficients of NaCl and NaHCO3 were also found to be similar in both the neonatal and adult proximal tubules. Thus neonatal and adult juxtamedullary PCT have many characteristics of water transport that are identical; however, neonatal Pf is three to five times that of the adult value. This difference in Pf with identical PDW values may give an insight into the transepithelial pathway for water movement in the neonatal tubule.

Renal Reabsorption of Water. Are there Pores in Proximal Tubule Cells?

Physiology ◽  
1988 ◽  
Vol 3 (2) ◽  
pp. 61-65 ◽  
Author(s):  
G Whittembury ◽  
P Carpi-Medina
Keyword(s):  
Proximal Tubule ◽  
Water Movement ◽  
Water Molecules ◽  
Toad Urinary Bladder ◽  
Sulfhydryl Reagents ◽  
Proximal Tubule Cells ◽  
Single File ◽  
Tubule Cells ◽  
Large Water ◽  
Human Red Cells

Transcellular water movement occurs mainly through water channels where water molecules move in single file. These channels, which explain the large water permeability of the proximal tubule cells, are closed by mercurial sulfhydryl reagents. There are similarities between these channels and those of human red cells and those that appear in distal nephron segments and toad urinary bladder after antidiuretic hormone stimulation.

Scaling Description of Sub-Monolayer Epitaxial Growth

1992 ◽  
Vol 280 ◽  
Author(s):  
A. Zangwill
Keyword(s):  
Epitaxial Growth ◽  
Surface Diffusion ◽  
Diffusion Constant ◽  
Current Status ◽  
Future Research ◽  
Deposition Flux ◽  
Simple Relationship ◽  
Island Nucleation ◽  
Scanning Tunnelling ◽  
Tunnelling Microscopy

ABSTRACTRecent experimental results aimed at the measurement of surface diffusion constants by use of scanning tunnelling microscopy and diffraction techniques have reawakened interest in the statistical properties of two-dimensional island nucleation and growth in the submonolayer regime. Classical homogeneous rate equation studies published over twenty years ago established a simple relationship among the number density of stable islands, the deposition flux, and the adatom surface diffusion constant. Recent Monte Carlo simulation studies confirm this prediction and considerably extend the scope of such a scaling description of submonolayer epitaxial growth. In this article, I review the current status of theory and experiment in this area and suggest some areas for future research.

Single Proximal Tubules of the Necturus Kidney. Methods for Micropuncture and Microperfusion

1958 ◽  
Vol 195 (3) ◽  
pp. 563-569 ◽  
Author(s):  
Joseph C. Shipp ◽  
Irwin B. Hanenson ◽  
Erich E. Windhager ◽  
Hans J. Schatzmann ◽  
Guillermo Whittembury ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Water Movement ◽  
Electrolyte Composition ◽  
Stopped Flow ◽  
Perfusion Fluid ◽  
Necturus Maculosus ◽  
Flow Perfusion ◽  
Tubular Lumen ◽  
Arbitrary Period

Procedures for the collection of tubular fluid and for stopped flow perfusions of the single proximal tubule of the kidney of Necturus maculosus are described. The method used in collection experiments is essentially the same as that developed by Richards and Walker ( Am. J. Physiol. 118: 111, 1937). The method used for stopped flow perfusion is a modification of the method of these authors. A proximal tubule in vivo is blocked with oil at both ends and the intervening space is filled with a perfusion fluid. After a suitable period (for instance, 20 min.), the fluid is withdrawn. By this method perfusion fluids of any desired composition are allowed to remain within the tubular lumen for an arbitrary period of time prior to collection and analysis. Water movement in the tubule is measured using C14 inulin. 27 samples of ureteral urine collected from 10 animals had a Na concentration of 2.8 ± 1.7 mEq/l. Data on the electrolyte composition of Necturus blood are presented, consistent with values given by other authors.

DETERMINATION OF THE FREE FLOW DEPTH UNDER UNEVEN CURRENT MODE IN PRISMATIC CHANNELS

2020 ◽  
pp. 116-122
Author(s):  
A.P. GURYEV ◽  
◽  
B.A. HAEK ◽  
Keyword(s):  
Energy Equation ◽  
Water Movement ◽  
Direct Calculation ◽  
Current Mode ◽  
Free Flow ◽  
Flow Depth ◽  
Flow Energy ◽  
Flow Parameters ◽  
Sequential Approximation ◽  
Channel Slope

The aim of the work is to analyze the existing method of calculating the spillway from the depth of the free flow under uneven mode in prismatic channels with a slowly changing movement and to develop a method of calculations that allows applying it to any flows in a prismatic channel without using any special tables. The existing methods for calculating flow parameters are based on the use of the Chesy formula to determine the flow consumption with a slowly changing water movement. At the same time, there is a V.I. Charnomsky’s method of direct calculation of the flow parameters from the energy equation without limiting the value of the channel slope. The disadvantage of this method is a possibility to solve the energy equation by the method of sequential approximation since the flow energy equation includes two variables, the flow depth and the distance between the sections. To eliminate this difficulty, it is proposed to determine the distance between the depths that make up the geometric progression on the considered part of the channel which allows calculating parameters of the free fl ow surface for any channel slopes and hydraulic flow modes without to special tables.

Permeability changes in Necturus proximal tubule during volume expansion

1978 ◽  
Vol 234 (3) ◽  
pp. F225-F234 ◽  
Author(s):  
C. J. Bentzel ◽  
P. R. Reczek
Keyword(s):  
Proximal Tubule ◽  
Volume Expansion ◽  
Dominant Role ◽  
Extracellular Volume ◽  
Water Flux ◽  
Apical Surface ◽  
Osmotic Flow ◽  
Flow Parameters ◽  
Diffusional Permeability ◽  
Necturus Proximal Tubule

The permeability of Necturus proximal tubule to hydrophilic nonelectrolytes of varying molecular size was studied under control conditions and during isotonic expansion of the animal's extracellular volume. Transepithelial permeability was measured in perfused tubular segments under conditions of zero net water flux. During volume expansion, tubular permeability to urea increased slightly, whereas mannitol decreased slightly and permeability to sucrose was significantly decreased. Volume expansion had a greater effect on osmotic flow parameters; the NaCl reflection coefficient decreased from 0.64 to 0.47 (summer animals) and from 0.41 to 0.27 (winter animals). Osmotic water flux and hydraulic conductivity increased but only in the lumen-to-capillary direction. Reflection coefficients of nonelectrolytes measured at the apical surface were reduced during volume expansion for probing molecules greater than 3 A in radius and were unchanged for smaller molecules, less than 3 A, suggesting two pore populations. We propose that an increase in tight-junction permeability can account for modification of osmotic flow parameters, whereas the whole thickness of the epithelium, particularly the intercellular space, plays the dominant role in regulation of diffusional permeability.

Transtubular Water Movement in the Isolated Doubly-Perfused Bullfrog Kidney

1956 ◽  
Vol 184 (3) ◽  
pp. 535-541 ◽  
Author(s):  
Robert E. Swanson ◽  
T. Hoshiko ◽  
M. B. Visscher
Keyword(s):  
Proximal Tubule ◽  
Water Movement ◽  
Deuterium Oxide ◽  
Flow Distribution ◽  
Portal System ◽  
Two Fluids ◽  
Peritubular Capillaries ◽  
Glomerular Filtrate ◽  
Inhomogeneous Flow ◽  
Capillary Fluid

Deuterium oxide (D2O) was perfused through either the arterial or the portal system of the isolated doubly-perfused bullfrog kidney. Admixture of the two fluids at the level of the peritubular capillaries makes it possible to regulate independently the composition of the glomerular filtrate and the peritubular fluid. The appearance of large amounts of labeled water in the urine when D2O was perfused through the portal system demonstrates a bidirectional water movement across the renal tubule. Furthermore the urine D2O concentration was, on the average, between 80–90% that of the renal vein perfusate (the latter was assumed to be similar in composition to peritubular capillary fluid). The apparent failure to reach complete equilibrium was shown to be due to an inhomogeneous flow distribution within the kidney. When the flow pattern was determined and the urine D2O content predicted on that basis, 100% equilibration of the isotope was established. These results are in agreement with the prediction, based on present concepts of proximal tubule water reabsorption, that tubule fluid should be 90% equilibrated before 1% of the proximal tubule is traversed.

scholarly journals Protein diffusion on membrane domes, tubes and pearling structures

2020 ◽  
Author(s):  
R. Rojas Molina ◽  
S. Liese ◽  
A. Carlson
Keyword(s):  
Diffusion Time ◽  
Simple Relationship ◽  
Half Time ◽  
Protein Diffusion ◽  
Protein Distribution ◽  
Membrane Morphology ◽  
Complex Shapes ◽  
Membrane Geometry ◽  
Shape Complexity ◽  
Membrane Shape

AbstractDiffusion is a fundamental mechanism for protein distribution in cell membranes. These membranes often exhibit complex shapes, which range from shallow domes to elongated tubular or pearl-like structures. Shape complexity of the membrane influences the diffusive spreading of proteins and molecules. Despite the importance membrane geometry plays in these diffusive processes, it is challenging to establish the dependence between diffusion and membrane morphology. We solve the diffusion equation numerically on various curved shapes representative for experimentally observed membrane shapes. Our results show that membrane necks become diffusion barriers. We determine the diffusive half time, i.e., the time that is required to reduce the amount of proteins in the budded region by one half and find a quadratic relation between the diffusive half time and the averaged mean curvature of the membrane shape. Our findings thus help to estimate the characteristic diffusive time scale based on the simple measure for membrane morphology.Significance statementDiffusion is an integral process for distributing proteins throughout biological membranes. These membranes can have complex shapes and structures, often featuring elongated shapes such as tubes and like a necklace of pearls. The diffusion process on these shapes is significantly different from the well studied planar substrate. We use numerical simulations to understand how the characteristic diffusion time is a function of membrane shape, where we find the diffusion of proteins on strongly curved shapes is significantly slower than on planar membranes. Our results provide a simple relationship to estimate the characteristic diffusion time of proteins on membranes based on its mean and Gaussian curvature.

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