Urea gradient-associated fluid absorption with sigma urea = 1 in rat terminal collecting duct

1990 ◽  
Vol 258 (5) ◽  
pp. F1173-F1180 ◽  
Author(s):  
C. L. Chou ◽  
J. M. Sands ◽  
H. Nonoguchi ◽  
M. A. Knepper
Keyword(s):  
Mathematical Model ◽  
Absorption Rate ◽  
Collecting Duct ◽  
Null Point ◽  
Absorption Measurement ◽  
Urea Transport ◽  
Fluid Absorption ◽  
A Value ◽  
Collecting Ducts ◽  
Isolated Rat

It has been proposed that inner medullary collecting ducts (IMCDs) can absorb fluid in the absence of a transepithelial osmolality gradient if a perfusate-to-bath urea gradient is present. Such a process has been suggested to be caused by a nonunity reflection coefficient for urea (sigma urea less than 1). However, our recent measurements of sigma urea yielded values not significantly different from 1.0. The present study was done to readdress the possibility of direct coupling of water and urea transport in the rat IMCD. Isolated rat terminal IMCD segments were studied in the presence of 10(-10) M vasopressin with the osmolality of the perfusate equal to that of the peritubular bath but with a perfusate-to-bath urea gradient (bath osmolality balanced with NaCl). We measured both fluid absorption rate and urea concentration in collected fluid and calculated the osmolality of the collected fluid. We observed rapid fluid absorption associated with substantial urea absorption. The urea absorption caused a large fall in the osmolality of the collected fluid with respect to the bath. Simulations with a mathematical model of an isolated perfused tubule revealed that the transepithelial osmolality gradient generated along the length of tubule (caused by urea absorption) was large enough to account for the fluid absorption. Measurement of sigma urea with the "zero-flux" (or null point) method revealed a value of 1.00 +/- 0.02. Thus we conclude that the observed fluid absorption is the result of a transepithelial osmolality gradient generated by rapid urea absorption and does not require sigma urea less than one.

scholarly journals Glucocorticoids downregulate the vasopressin-regulated urea transporter in rat terminal inner medullary collecting ducts.

1997 ◽  
Vol 8 (4) ◽  
pp. 517-523 ◽  
Author(s):  
M Naruse ◽  
J D Klein ◽  
Z M Ashkar ◽  
J D Jacobs ◽  
J M Sands
Keyword(s):  
Collecting Duct ◽  
Northern Analysis ◽  
Sham Operation ◽  
Urea Transport ◽  
Urea Transporter ◽  
Transporter Protein ◽  
Urea Permeability ◽  
Collecting Ducts ◽  
Medullary Collecting Duct ◽  
Adrenalectomized Rats

This study tested whether glucocorticoids regulate tubular urea transport. Urea permeability was measured in perfused inner medullary collecting duct (IMCD) subsegments from rats that underwent adrenalectomy, adrenalectomy plus replacement with a physiologic dose of glucocorticoid (dexamethasone), or sham operation. Compared with sham rats, basal urea permeability in terminal IMCD was significantly increased in adrenalectomized rats and reduced in dexamethasone-treated rats. Vasopressin significantly increased urea permeability in all three groups. In contrast, there was no difference in basal or vasopressin-stimulated urea permeability in initial IMCD between the three groups. Next, membrane and vesicle fraction proteins were isolated from inner medullary tip or base and Western analysis was performed by use of an antibody to the rat vasopressin-regulated urea transporter. Vasopressin-regulated urea transporter protein was significantly increased in both membrane and vesicle fractions from the inner medullary tip of adrenalectomized rats. There was no change in vasopressin-regulated urea transporter protein in the inner medullary base, and Northern analysis showed no change in urea transporter mRNA abundance in either inner medullary region. It was concluded that glucocorticoids can downregulate function and expression of the vasopressin-regulated urea transporter in rat terminal IMCD.

Mathematical model of an avian urine concentrating mechanism

2000 ◽  
Vol 279 (6) ◽  
pp. F1139-F1160 ◽  
Author(s):  
H. E. Layton ◽  
John M. Davies ◽  
Giovanni Casotti ◽  
Eldon J. Braun
Keyword(s):  
Mathematical Model ◽  
Flow Parameter ◽  
Urine Osmolality ◽  
Energetic Cost ◽  
Loop Of Henle ◽  
Nacl Transport ◽  
A Value ◽  
Concentrating Mechanism ◽  
Collecting Ducts ◽  
Urine Concentrating Mechanism

A mathematical model was used to investigate how concentrated urine is produced within the medullary cones of the quail kidney. Model simulations were consistent with a concentrating mechanism based on single-solute countercurrent multiplication and on NaCl cycling from ascending to descending limbs of loops of Henle. The model predicted a urine-to-plasma (U/P) osmolality ratio of ∼2.26, a value consistent with maximum avian U/P osmolality ratios. Active NaCl transport from descending limb prebend thick segments contributed 70% of concentrating capability. NaCl entry and water extraction provided 80 and 20%, respectively, of the concentrating effect in descending limb flow. Parameter studies indicated that urine osmolality is sensitive to the rate of fluid entry into descending limbs and collecting ducts at the cone base. Parameter studies also indicated that the energetic cost of concentrating urine is sensitive to loop of Henle population as a function of medullary depth: as the fraction of loops reaching the cone tip increased above anatomic values, urine osmolality increased only marginally, and, ultimately, urine osmolality decreased.

Thiazide-sensitive NaCl absorption in rat cortical collecting duct

1990 ◽  
Vol 259 (3) ◽  
pp. F519-F528 ◽  
Author(s):  
Y. Terada ◽  
M. A. Knepper
Keyword(s):  
Collecting Duct ◽  
Sodium Absorption ◽  
Cortical Collecting Duct ◽  
Fluid Absorption ◽  
Secondary Active Transport ◽  
Nacl Transport ◽  
Transport Pathways ◽  
Chloride Absorption ◽  
Collecting Ducts ◽  
Transepithelial Voltage

The mechanism of transepithelial NaCl transport was investigated in isolated perfused cortical collecting ducts from the kidneys of deoxycorticosterone-treated rats. In the presence of vasopressin, hydrochlorothiazide (0.1 mM) markedly reduced the net rate of Na absorption, Cl absorption, and active fluid absorption but did not significantly change the transepithelial voltage. Similarly, in the absence of vasopressin, hydrochlorothiazide decreased the rate of sodium absorption by 50% without affecting transepithelial voltage. Amiloride (30 microM) completely eliminated the lumen-negative voltage but decreased net sodium absorption only by approximately 50%. In the presence of amiloride, chloride absorption occurred against an electrochemical gradient for chloride, indicating that there was active chloride absorption. Bumetanide (0.1 mM) did not affect chloride absorption or spontaneous fluid absorption in the presence of vasopressin. The combination of amiloride and hydrochlorothiazide inhibited net sodium absorption by a greater extent than did either agent alone. These results demonstrate the presence of the following two parallel sodium transport pathways in cortical collecting ducts from mineralocorticoid-replete rats: 1) an electrogenic pathway blocked by amiloride, which presumably involves an apical sodium channel, and 2) a thiazide-inhibitable electroneutral pathway, which presumably utilizes apical Na-Cl cotransport and mediates secondary active transport of chloride.

scholarly journals Potassium depletion increases proton pump (H+-ATPase) activity in intercalated cells of cortical collecting duct

2000 ◽  
Vol 279 (1) ◽  
pp. F195-F202 ◽  
Author(s):  
Randi B. Silver ◽  
Sylvie Breton ◽  
Dennis Brown
Keyword(s):  
Plasma Membrane ◽  
Atpase Activity ◽  
Collecting Duct ◽  
Proton Pumps ◽  
Intercalated Cells ◽  
Cortical Collecting Duct ◽  
Collecting Ducts ◽  
Acid Load ◽  
Collecting Tubules ◽  
Atpase Staining

Intercalated cells (ICs) from kidney collecting ducts contain proton-transporting ATPases (H+-ATPases) whose plasma membrane expression is regulated under a variety of conditions. It has been shown that net proton secretion occurs in the distal nephron from chronically K+-depleted rats and that upregulation of tubular H+- ATPase is involved in this process. However, regulation of this protein at the level of individual cells has not so far been examined. In the present study, H+-ATPase activity was determined in individually identified ICs from control and chronically K+-depleted rats (9–14 days on a low-K+ diet) by monitoring K+- and Na+-independent H+ extrusion rates after an acute acid load. Split-open rat cortical collecting tubules were loaded with the intracellular pH (pHi) indicator 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, and pHiwas determined by using ratiometric fluorescence imaging. The rate of pHi recovery in ICs in response to an acute acid load, a measure of plasma membrane H+-ATPase activity, was increased after K+ depletion to almost three times that of controls. Furthermore, the lag time before the start of pHirecovery after the cells were maximally acidified fell from 93.5 ± 13.7 s in controls to 24.5 ± 2.1 s in K+-depleted rats. In all ICs tested, Na+- and K+-independent pHi recovery was abolished in the presence of bafilomycin (100 nM), an inhibitor of the H+-ATPase. Analysis of the cell-to-cell variability in the rate of pHi recovery reveals a change in the distribution of membrane-bound proton pumps in the IC population of cortical collecting duct from K+-depleted rats. Immunocytochemical analysis of collecting ducts from control and K+-depleted rats showed that K+-depletion increased the number of ICs with tight apical H+ATPase staining and decreased the number of cells with diffuse or basolateral H+-ATPase staining. Taken together, these data indicate that chronic K+ depletion induces a marked increase in plasma membrane H+ATPase activity in individual ICs.

Automated method for the isolation of collecting ducts

2006 ◽  
Vol 291 (1) ◽  
pp. F236-F245 ◽  
Author(s):  
R. Lance Miller ◽  
Ping Zhang ◽  
Tong Chen ◽  
Andreas Rohrwasser ◽  
Raoul D. Nelson
Keyword(s):  
Flow Cytometry ◽  
Large Particle ◽  
Fluorescent Protein ◽  
Collecting Duct ◽  
Complex Object ◽  
Cortical Collecting Duct ◽  
Fluorescent Intensity ◽  
Automated Method ◽  
Collecting Ducts ◽  
Time Required

The structural and functional heterogeneity of the collecting duct present a tremendous experimental challenge requiring manual microdissection, which is time-consuming, labor intensive, and not amenable to high throughput. To overcome these limitations, we developed a novel approach combining the use of transgenic mice expressing green fluorescent protein (GFP) in the collecting duct with large-particle-based flow cytometry to isolate pure populations of tubular fragments from the whole collecting duct (CD), or inner medullary (IMCD), outer medullary (OMCD), or connecting segment/cortical collecting duct (CNT/CCD). Kidneys were enzymatically dispersed into tubular fragments and sorted based on tubular length and GFP intensity using large-particle-based flow cytometry or a complex object parametric analyzer and sorter (COPAS). A LIVE/DEAD assay demonstrates that the tubules were >90% viable. Tubules were collected as a function of fluorescent intensity and analyzed by epifluorescence and phase microscopy for count accuracy, GFP positivity, average tubule length, and time required to collect 100 tubules. Similarly, mRNA and protein from sorted tubules were analyzed for expression of tubule segment-specific genes using quantitative real-time RT-PCR and immunoblotting. The purity and yield of sorted tubules were related to sort stringency. Four to six replicates of 100 collecting ducts (9.68 ± 0.44–14.5 ± 0.66 cm or 9.2 ± 0.7 mg tubular protein) were routinely obtained from a single mouse in under 1 h. In conclusion, large-particle-based flow cytometry is fast, reproducible, and generates sufficient amounts of highly pure and viable collecting ducts from single or replicate animals for gene expression and proteomic analysis.

The mechanisms of urea transport by early life stages of rainbow trout (Oncorhynchus mykiss)

2000 ◽  
Vol 203 (20) ◽  
pp. 3199-3207 ◽  
Author(s):  
C.M. Pilley ◽  
P.A. Wright
Keyword(s):  
Rainbow Trout ◽  
Oncorhynchus Mykiss ◽  
Urea Transport ◽  
Early Life Stages ◽  
Urea Transporter ◽  
Urea Excretion ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Collecting Ducts ◽  
External Water ◽  
Very High

We tested the hypothesis that urea transport in rainbow trout (Oncorhynchus mykiss) embryos is dependent, in part, on a bidirectional urea-transport protein. Acute exposure to phloretin and urea analogs [acetamide, thiourea, 1,(4-nitrophenyl)-2-thiourea] reversibly inhibited urea excretion from the embryos to the external water. Unidirectional urea influx was inhibited by acetamide and thiourea, with IC(50) values of 0.04 and 0.05 mmol l(−1), respectively. Influx of urea from the external water to the embryo tended to saturate at elevated external urea concentrations (V(max)=10.50 nmol g(−1) h(−1); K(m)=2 mmol l(−1)). At very high urea concentrations (20 mmol l(−1)), however, a second, non-saturable component was apparent. These results indicate that urea excretion in trout embryos is dependent, in part, on a phloretin-sensitive facilitated urea transporter similar to that reported in mammalian inner medullary collecting ducts and elasmobranch kidney.

Relationship between interdigestive duodenal motility and fluid transport in humans

1990 ◽  
Vol 259 (3) ◽  
pp. G348-G354 ◽  
Author(s):  
H. Sjovall ◽  
I. Hagman ◽  
H. Abrahamsson
Keyword(s):  
Motor Activity ◽  
Phase Ii ◽  
Absorption Rate ◽  
Fluid Transport ◽  
Late Phase ◽  
Fluid Absorption ◽  
Amylase Release ◽  
Duodenal Fluid ◽  
Interdigestive Motility ◽  
Motility Cycle

In 22 healthy volunteers distal duodenal fluid absorption was related to the interdigestive motility cycle. Fluid absorption was measured with a triple-lumen perfusion technique, and motility was registered with a low-compliance pneumohydraulic system. Pancreatic and biliary secretions were estimated by measurement of bilirubin and amylase release into the duodenal segment. Duodenal fluid absorption rate changed during the interdigestive motility cycle; the highest absorption rate was registered during phase I (low-motor activity) and absorption rate then decreased in parallel with increasing motor activity during phase II (r = -0.69, P less than 0.001). In late phase II a net fluid secretion was frequently registered, together with an increased release of bilirubin into the duodenal lumen. This pattern was seen during perfusion with both glucose-containing (30 mM) and glucose-free solutions. The results show that duodenal fluid absorption rate changes markedly during the interdigestive motility cycle. This effect may be a hydrodnamic phenomenon or may be due to activation of a neural secretory mechanism during phase II.

A mathematical model of rat collecting duct II. Effect of buffer delivery on urinary acidification

2002 ◽  
Vol 283 (6) ◽  
pp. F1252-F1266 ◽  
Author(s):  
Alan M. Weinstein
Keyword(s):  
Mathematical Model ◽  
Carbonic Anhydrase ◽  
Collecting Duct ◽  
Phosphate Concentration ◽  
Rate Coefficients ◽  
Urinary Flow ◽  
Urinary Acidification ◽  
Model Predictions ◽  
Disequilibrium Ph ◽  
Urinary Acid

A mathematical model of the rat collecting duct (CD) is used to examine the effect of delivered load of bicarbonate and nonbicarbonate buffer on urinary acidification. Increasing the delivered load of HCO[Formula: see text] produces bicarbonaturia, and, with luminal carbonic anhydrase absent, induces a disequilibrium luminal pH and a postequilibration increase in urinary Pco 2. At baseline flows, this disequilibrium disappears when luminal carbonic anhydrase rate coefficients reach 1% of full catalysis. The magnitude of the equilibration Pco 2 depends on the product of urinary acid phosphate concentration and the disequilibrium pH. Thus, although increasing phosphate delivery to the CD decreases the disequilibrium pH, the increase in urinary phosphate concentration yields an overall increase in postequilibration Pco 2. In simulations of experimental HCO[Formula: see text] loading in the rat, model predictions of urinary Pco 2 exceed the measured Pco 2 of bladder urine. In part, the higher model predictions for urinary Pco 2 may reflect higher urinary flow rates and lower urinary phosphate concentrations in the experimental preparations. However, when simulation of CD function during HCO[Formula: see text] loading acknowledges the high ambient renal medullary Pco 2 (5), the predicted urinary Pco 2 of the model CD is yet that much greater. This discrepancy cannot be resolved within the model but requires additional experimental data, namely, concomitant determination of urinary buffer concentrations within the tubule fluid sampled for Pco 2 and pH. This model should provide a means for simulating formal testing of urinary acidification and thus for examining hypotheses regarding transport defects underlying distal renal tubular acidosis.

Vasopressin receptor subtype 2 activation increases cell proliferation in the renal medulla of AQP1 null mice

2007 ◽  
Vol 293 (6) ◽  
pp. F1858-F1864 ◽  
Author(s):  
Qi Cai ◽  
Matthew R. McReynolds ◽  
Maggie Keck ◽  
Kevin A. Greer ◽  
James B. Hoying ◽  
...  
Keyword(s):  
Cyclin D1 ◽  
Collecting Duct ◽  
Renal Medulla ◽  
Nuclear Antigen ◽  
Receptor Subtype ◽  
Protein Abundance ◽  
Activating Transcription Factor 3 ◽  
Collecting Ducts ◽  
Growth Changes ◽  
Activating Transcription Factor

Aquaporin (AQP) 1 null mice have a defect in the renal concentrating gradient because of their inability to generate a hyperosmotic medullary interstitium. To determine the effect of vasopressin on renal medullary gene expression, in the absence of high local osmolarity, we infused 1-deamino-8-d-arginine vasopressin (dDAVP), a V2 receptor (V2R)-specific agonist, in AQP1 null mice for 7 days. cDNA microarray analysis was performed on the renal medullary tissue, and 5,140 genes of the possible 12,000 genes on the array were included in the analysis. In the renal medulla of AQP1 null mice, 245 transcripts were identified as increased by dDAVP infusion and 200 transcripts as decreased (1.5-fold or more). Quantitative real-time PCR measurements confirmed the increases seen for cyclin D1, early growth response gene 1, and activating transcription factor 3, genes associated with changes in cell cycle/growth. Changes in mRNA expression were correlated with changes in protein expression by semiquantitative immunoblotting; cyclin D1 and ATF3 were increased significantly in abundance following dDAVP infusion in the renal medulla of AQP1 null mice (161 and 461%, respectively). A significant increase in proliferation of medullary collecting ducts cells, following V2R activation, was identified by proliferating cell nuclear antigen immunohistochemistry; colocalization studies with AQP2 indicated that the increase in proliferation was primarily observed in principal cells of the inner medullary collecting duct (IMCD). V2R activation, via dDAVP, increased AQP2 and AQP3 protein abundance in the cortical collecting ducts of AQP1 null mice. However, V2R activation did not increase AQP2 protein abundance in the IMCD of AQP1 null mice.

scholarly journals Airborne infection in a fully air-conditioned hospital: III. Transport of gaseous and airborne particulate material along ventilated passageways

1975 ◽  
Vol 75 (1) ◽  
pp. 45-56 ◽  
Author(s):  
O. M. Lidwell
Keyword(s):  
Mathematical Model ◽  
Flow Velocity ◽  
Effective Diffusion ◽  
Diffusion Constant ◽  
Particulate Material ◽  
Airborne Particulate ◽  
Airborne Infection ◽  
Directional Flow ◽  
A Value

SUMMARYA mathematical model is described for the transport of gaseous or airborne particulate material between rooms along ventilated passageways.Experimental observations in three hospitals lead to a value of about 0.06m.2/sec. for the effective diffusion constant in air without any systematic directional flow. The ‘constant’ appears to increase if there is any directional flow along the passage, reaching about 0.12 m.2/sec. at a flow velocity of 0.04 m./sec.Together with previously published methods the present formulae make it possible to calculate the expected average amounts of gaseous or particulate material that will be transported from room to room in ventilated buildings in which the ventilation and exchange airflows can be calculated.The actual amounts transported in occupied buildings, however, vary greatly from time to time.

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