Determination of the apparent transport constants for urate absorption in the rat proximal tubule

1981 ◽  
Vol 240 (5) ◽  
pp. F406-F410
Author(s):  
S. C. Sansom ◽  
H. O. Senekjian ◽  
T. F. Knight ◽  
H. Babino ◽  
D. Steplock ◽  
...  
Keyword(s):  
Reflection Coefficient ◽  
Proximal Tubule ◽  
Continuous Flow ◽  
Active Component ◽  
Solvent Drag ◽  
Perfusion Solution ◽  
Saturation Kinetics ◽  
Rat Proximal Tubule ◽  
Independent Confirmation

Using continuous-flow luminal microperfusion techniques, the influence of the intraluminal urate concentration on urate absorption was determined in the rat proximal tubule. When the estimated contribution of passive permeation was accounted for, the “active” component of urate absorption demonstrated saturation kinetics. The apparent Km was 0.17 mM and the Vmax 0.31 pmol.min-1.mm-1. These transport constants were similar when derived from either a water-absorbing or steady-state equilibrium perfusion solution. The reflection coefficient was determined in studies employing the techniques of simultaneous capillary and luminal microperfusion. Both perfusion solutions contained p-chloromercuribenzoate to inhibit active urate transport. In the presence or absence of an osmole gradient imposed across the tubule, the reflection coefficient for urate averaged 0.94. These studies provide evidence that urate absorption in the rat proximal tubule is a carrier-mediated process. They also provide independent confirmation of the passive flux coefficient derived in prior studies. Finally, the results suggest that solvent drag would have little effect on urate absorption.

Effects of intraluminal D-glucose and probenecid on urate absorption in the rat proximal tubule

1979 ◽  
Vol 236 (6) ◽  
pp. F526-F529 ◽  
Author(s):  
T. F. Knight ◽  
H. O. Senekjian ◽  
S. Sansom ◽  
E. J. Weinman
Keyword(s):  
Proximal Tubule ◽  
Water Absorption ◽  
Rat Kidney ◽  
Proximal Convoluted Tubule ◽  
Perfusion Solution ◽  
Hexose Sugars ◽  
Tubular Absorption ◽  
Rat Proximal Tubule ◽  
Fractional Absorption

The in vivo microperfusion technique was employed to examine urate absorption in the proximal convoluted tubule of the rat kidney using [2–14C]urate as the marker for fractional urate absorption. With NaCl as the perfusion solution, water absorption averaged 2.53 +/- 0.16 nl.min-1.mm tubule-1, and the fractional absorption of [2–14C]urate averages 11.6 +/- 1.0%/mm tubule. The addition of D-glucose (50 mg/100 ml) enhanced water absorption to 3.62 +/- 0.19 nl.min-1.mm tubule-1, but inhibited fractional urate absorption to 6.6 +/- 1.2%/mm tubule. Phloridzin (4.4 mg/100 ml), 2-deoxy-D-glucose (45.6 mg/100 ml), and 3-O-methyl-D-glucose (53.9 mg/100 ml) also inhibited the absorption of [2–14C]urate to the same degree as did D-glucose despite differing effects on water absorption. The addition of probenecid (2.8 mg/100 ml) to the NaCl perfusion solution had no effect on water absorption but inhibited [2–14C]urate absorption to 6.4 +/- 0.6%/mm tubule. The addition of both probenecid and phloridzin further reduced [2–14C-A1urate absorption to 3.8 +/- 0.7%/mm tubule. Probenecid alone had no effect on glucose transport. These studies suggest that the presence of either certain hexose sugars, phloridzin, or probenecid in the lumen of the proximal convoluted tubule inhibits the tubular absorption of urate.

Integral-mass balance method for determination of solvent drag reflection coefficient

1987 ◽  
Vol 253 (1) ◽  
pp. H194-H204 ◽  
Author(s):  
M. B. Wolf ◽  
P. D. Watson ◽  
D. R. Scott
Keyword(s):  
Reflection Coefficient ◽  
Mass Balance ◽  
Measurement Errors ◽  
Plasma Proteins ◽  
Solvent Drag ◽  
Fluid Filtration ◽  
Mean Values ◽  
Macromolecular Transport ◽  
Mass Balance Method

We have developed the integral-mass balance (IMB) method to measure the solvent drag reflection coefficient (sigma f) for transcapillary macromolecular transport in skeletal muscle and other organs. Of course, sigma f is calculated from the cumulative amounts of water and macromolecule that move convectively across the microvascular membrane as determined from changes in hematocrit and plasma macromolecule concentration over a period of fluid filtration. We have investigated the effects of both theoretical and experimental factors that affect the validity and accuracy of the method. The effect of the following factors on sigma f determination by the IMB method were explored: low Peclet number; random-measurement errors; and systematic errors due to vascular leakage, hemolysis of red blood cells, evaporation, and osmolality changes. We found that all of these factors produced overestimations of sigma f, but their effects could be corrected. Also, appropriate experimental design could minimize these effects. Experiments using the IMB method in the isolated, perfused cat hindlimb preparation to determine sigma f for albumin and plasma proteins resulted in mean values of 0.82 +/- 0.08 (SD) (n = 7) and 0.83 +/- 0.02 (n = 4), respectively.

Secretion of urate in the proximal convoluted tubule of the rat

1980 ◽  
Vol 239 (4) ◽  
pp. F383-F387 ◽  
Author(s):  
E. J. Weinman ◽  
S. C. Sansom ◽  
D. A. Steplock ◽  
A. U. Sheth ◽  
T. F. Knight ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
High Performance ◽  
Competitive Inhibitor ◽  
Capillary Perfusion ◽  
Perfusion Solution ◽  
Organic Acid Secretion ◽  
Net Flux ◽  
Rat Proximal Tubule ◽  
Urate Secretion

In order to examine the transepithelial secretory flux of urate in the rat proximal tubule, simultaneous perfusions of capillaries and lumens were performed. The capillary perfusate contained [2–14C]urate in concentrations of 0.305–2.941 mM. The secretory flux of urate increased as the concentration of urate in the capillary perfusion solution was increased from 0.305 to 1.235 mM but tended toward a plateau at higher concentrations. An apparent Km of 0.41 mM and Vmax of 4.7 pmol·min-1·mm-1 were calculated from the observed net flux and an estimated passive permeability coefficient of 0.725 pmol·min-1·mm-1. The addition of probenecid (10-4 M) to the capillary perfusion solution inhibited urate secretion in a manner consistent with that of a competitive inhibitor. The addition of p-chloromercuribenzoate (10-4 M) to the capillary perfusion solution inhibited the Vmax but not the Km, suggesting a non-competitive type of inhibition. These data provide the first estimates of the apparent transport constants for urate secretion in the rat proximal tubule determined in vivo. Urate secretion is mediated by a saturable carrier-mediated system. This carrier is not affected by the presence or absence of potassium in the perfusion solution but can be inhibited by the addition of either probenecid or p-chloromercuribenzoate. high-performance liquid chromatography with electrochemical detection; renal micropunction; organic acid secretion Submitted on March 5, 1980 Accepted on April 25, 1980

Transport by epithelia with compliant lateral intercellular spaces: asymmetric oncotic effects across the rat proximal tubule

1984 ◽  
Vol 247 (5) ◽  
pp. F848-F862 ◽  
Author(s):  
A. M. Weinstein
Keyword(s):  
Reflection Coefficient ◽  
Proximal Tubule ◽  
Electrical Resistance ◽  
Volume Flow ◽  
Intercellular Spaces ◽  
Water Reabsorption ◽  
Solute Permeability ◽  
Lateral Intercellular Spaces ◽  
Rat Proximal Tubule

Mathematical models of the proximal tubule are considered in which the lateral intercellular spaces distend in response to increased interstitial pressures and basal outlet permeabilities increase as a result of interspace widening. An approximate analytical model of the interspace reveals the possibility that such compliance may introduce an asymmetry to the effect of protein oncotic forces on transepithelial volume flow. Peritubular oncotic forces close the interspace, enhance interspace hypertonicity, and thus substantially increase volume reabsorption (enhanced intraepithelial solute-solvent coupling). The model also predicts a decline in epithelial water permeability (Lp), salt reflection coefficient, and salt permeability, with the application of peritubular protein. When parameters are chosen so as to represent the rat proximal tubule, the predicted effect on solute permeability is comparable to the observed changes in electrical resistance of the epithelium. However, when the luminal solution is slightly hypotonic to blood and proximal reabsorption has become isosmotic, the models show relatively small protein effects, which are dependent upon cell and tight junction permeabilities and are little influenced by interspace compliance. The capability of such models to represent the peritubular protein enhancement of isosmotic salt and water reabsorption by the proximal tubule in vivo is questioned.

scholarly journals Solvent drag measurement of transcellular and basolateral membrane NaCl reflection coefficient in kidney proximal tubule.

1991 ◽  
Vol 98 (2) ◽  
pp. 379-398 ◽  
Author(s):  
L B Shi ◽  
K Fushimi ◽  
A S Verkman
Keyword(s):  
Mathematical Model ◽  
Reflection Coefficient ◽  
Proximal Tubule ◽  
Time Course ◽  
Basolateral Membrane ◽  
Rabbit Kidney ◽  
Solvent Drag ◽  
Ratio Imaging ◽  
Drag Measurement ◽  
Axial Profile

The NaCl reflection coefficient in proximal tubule has important implications for the mechanisms of near isosmotic volume reabsorption. A new fluorescence method was developed and applied to measure the transepithelial (sigma NaClTE) and basolateral membrane (sigma NaClcl) NaCl reflection coefficients in the isolated proximal straight tubule from rabbit kidney. For sigma NaClTE measurement, tubules were perfused with buffers containing 0 Cl, the Cl-sensitive fluorescent indicator 6-methoxy-N-[3-sulfopropyl] quinolinium and a Cl-insensitive indicator fluorescein sulfonate, and bathed in buffers of differing cryoscopic osmolalities containing NaCl. The transepithelial Cl gradient along the length of the tubule was measured in the steady state by a quantitative ratio imaging technique. A mathematical model based on the Kedem-Katchalsky equations was developed to calculate the axial profile of [Cl] from tubule geometry, lumen flow, water (Pf) and NaCl (PNaCl) permeabilities, and sigma NaClTE. A fit of experimental results to the model gave PNaCl = (2.25 +/- 0.2) x 10(-5) cm/s and sigma NaClTE = 0.98 +/- 0.03 at 23 degrees C. For measurement of sigma NaClbl, tubule cells were loaded with SPQ in the absence of Cl. NaCl solvent drag was measured from the time course of NaCl influx in response to rapid (less than 1 s) Cl addition to the bath solution. With bath-to-cell cryoscopic osmotic gradients of 0, -60, and +30 mosmol, initial Cl influx was 1.23, 1.10, and 1.25 mM/s; a fit to a mathematical model gave sigma NaClbl = 0.97 +/- 0.04. These results indicate absence of NaCl solvent drag in rabbit proximal tubule. The implications of these findings for water and NaCl movement in proximal tubule are evaluated.

Proximal tubule glucose efflux in the rat as a function of delivered load

1980 ◽  
Vol 238 (6) ◽  
pp. F499-F503 ◽  
Author(s):  
T. F. Knight ◽  
H. O. Senekjian ◽  
S. C. Sansom ◽  
E. J. Weinman
Keyword(s):  
Proximal Tubule ◽  
Glucose Concentration ◽  
Glucose Solution ◽  
Initial Glucose Concentration ◽  
Perfusion Solution ◽  
Glucose Flux ◽  
Flow Dependency ◽  
Absorptive Flux ◽  
Rat Proximal Tubule

The effect of altering the delivered load of glucose by either increasing the rate of perfusion or the initial glucose concentration on the absorptive flux of glucose was examined in rat proximal tubule using the in vivo microperfusion technique. The passive flux coefficient was determined to be 1.27 pmol . min-1 . mm-1 . mM-1 glucose concentration gradient. With initial glucose concentrations of either 11.1 or 22.2 mM, the glucose flux increased as the rate of perfusion was increased. At similar rates of perfusion, glucose flux was higher from 22.2 mM glucose solution than from the 11.1 mM solution. Estimation of the driving force for passive glucose efflux indicates that the increase in glucose efflux when flow rate is increased cannot be accounted for by passive changes in efflux out of the proximal tubule. When large transepithelial glucose gradients are imposed across the tubule, passive glucose flux plays a more significant role, but cannot totally account for higher rates of glucose efflux observed with the perfusion solution containing 22.2 mM glucose. These results are considered in light of the recent model of the flow dependency of nonelectrolyte absorption of Barfuss and Schafer [Am. J. Physiol. 236 (Renal Fluid Electrolyte Physiol. 5): F163–F174. 1979].

scholarly journals Microelectrode determination of pH and PCO2 in rat proximal tubule after benzolamide: Evidence for hydrogen ion secretion

1979 ◽  
Vol 15 (6) ◽  
pp. 624-629 ◽  
Author(s):  
Thomas D. DuBose ◽  
Leo R. Pucacco ◽  
Donald W. Seldin ◽  
Norman W. Carter ◽  
Juha P. Kokko
Keyword(s):  
Proximal Tubule ◽  
Hydrogen Ion ◽  
Ion Secretion ◽  
Rat Proximal Tubule

Reduction of Potassium in Kidney Proximal Tubules to Aid in Electron Probe X-Ray Microanalysis of Calcium

1985 ◽  
Vol 43 ◽  
pp. 474-475
Author(s):  
A. LeFurgey ◽  
P. Ingram ◽  
L.J. Mandel
Keyword(s):  
Smooth Muscle ◽  
Proximal Tubule ◽  
Electron Probe ◽  
Clinical Applications ◽  
Proximal Tubules ◽  
Rabbit Kidney ◽  
Target Cells ◽  
X Ray ◽  
Freeze Dried

For quantitative determination of subcellular Ca distribution by electron probe x-ray microanalysis, decreasing (and/or eliminating) the K content of the cell maximizes the ability to accurately separate the overlapping K Kß and Ca Kα peaks in the x-ray spectra. For example, rubidium has been effectively substituted for potassium in smooth muscle cells, thus giving an improvement in calcium measurements. Ouabain, a cardiac glycoside widely used in experimental and clinical applications, inhibits Na-K ATPase at the cell membrane and thus alters the cytoplasmic ion (Na,K) content of target cells. In epithelial cells primarily involved in active transport, such as the proximal tubule of the rabbit kidney, ouabain rapidly (t1/2= 2 mins) causes a decrease2 in intracellular K, but does not change intracellular total or free Ca for up to 30 mins. In the present study we have taken advantage of this effect of ouabain to determine the mitochondrial and cytoplasmic Ca content in freeze-dried cryosections of kidney proximal tubule by electron probe x-ray microanalysis.

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