Axial heterogeneity in the rat proximal convoluted tubule. I. Bicarbonate, chloride, and water transport

1984 ◽  
Vol 247 (5) ◽  
pp. F816-F821 ◽  
Author(s):  
F. Y. Liu ◽  
M. G. Cogan
Keyword(s):  
Proximal Tubule ◽  
Water Transport ◽  
Wistar Rats ◽  
Proximal Convoluted Tubule ◽  
Free Flow ◽  
Concentration Profiles ◽  
Transport Capacity ◽  
Water Reabsorption ◽  
Substrate Concentrations

To measure simultaneously the concentration profiles of bicarbonate, chloride and inulin along the length of the superficial proximal convoluted tubule, free-flow micropuncture measurements were made sequentially from the end-proximal tubule to Bowman's space in 10 tubules of hydropenic Munich-Wistar rats. Bicarbonate and volume reabsorption were 354 +/- 21 pmol X mm-1 X min-1 and 5.9 +/- 0.4 nl X mm-1 X min-1 in the first millimeter and fell progressively in the remaining 3.8 mm of tubule, averaging 83 +/- 4 pmol X mm-1 X min-1 and 2.3 +/- 0.5 nl X mm-1 X min-1, respectively. The values in the initial millimeter represents a high transport capacity since they exceed rates that have been observed when comparable or even higher mean luminal substrate concentrations were presented to the late proximal tubule. In contrast, chloride reabsorption was only 206 +/- 55 peq X mm-1 X min-1 in the first millimeter compared with a mean of 306 +/- 22 peq X mm-1 X min-1 in the rest of the tubule. In conclusion, there is substantial axial transport heterogeneity, with bicarbonate and water reabsorption higher but chloride reabsorption lower in the early compared with the late superficial proximal convoluted tubule.

Axial heterogeneity in the rat proximal convoluted tubule. II. Osmolality and osmotic water permeability

1984 ◽  
Vol 247 (5) ◽  
pp. F822-F826 ◽  
Author(s):  
F. Y. Liu ◽  
M. G. Cogan ◽  
F. C. Rector
Keyword(s):  
Proximal Tubule ◽  
Water Permeability ◽  
Driving Force ◽  
Wistar Rats ◽  
Proximal Convoluted Tubule ◽  
Osmotic Gradient ◽  
Osmotic Water Permeability ◽  
Water Reabsorption ◽  
Osmotic Water ◽  
Measured Water

To assess whether proximal luminal fluid becomes hypotonic with respect to plasma, free-flow micropuncture measurements were made sequentially from the end-proximal tubule to Bowman's space in 10 tubules of hydropenic Munich-Wistar rats. Osmolality in Bowman's space was 2.8 +/- 0.3 mosmol less than in plasma. Tubular fluid osmolality fell along the tubule and by the end-proximal tubule was 7.5 +/- 0.7 mosmol/kg less than in plasma or 4.7 mosmol/kg less than in Bowman's space. Since luminal fluid became hypotonic, the reabsorbate was hypertonic. The transepithelial osmotic water permeability (Pf) was calculated using simultaneously measured water reabsorption rates. The osmotic gradient responsible for water reabsorption was assumed to be either lumen-to-reabsorbate or lumen-to-peritubular plasma, with a reflection coefficient for sodium chloride of 0.7-1.0. The Pf was then estimated to be between 0.2 and 2.0 cm/s in the first millimeter of tubule and to have fallen to 0.1-0.2 cm/s by the end of the tubule. In conclusion, luminal hypotonicity develops in the rat proximal convoluted tubule and must be considered as part of the osmotic driving force for water reabsorption.

Water permeability and pathways in the proximal tubule

1983 ◽  
Vol 245 (3) ◽  
pp. F279-F294 ◽  
Author(s):  
C. A. Berry
Keyword(s):  
Proximal Tubule ◽  
Water Transport ◽  
Water Permeability ◽  
Intercellular Space ◽  
Proximal Convoluted Tubule ◽  
Pressure Gradients ◽  
Solvent Drag ◽  
Lateral Intercellular Space ◽  
Volume Absorption ◽  
Osmotic Water

The route of water transport in the proximal tubule could be either transjunctional or transcellular. A transjunctional route is supported by data showing high osmotic-to-diffusive water permeability ratios, the possible correlation of junctional leakiness to ions and nonelectrolytes with water permeability, and solvent drag of nonelectrolytes and ions. These data, however, are not convincing. A transcellular route of water transport is supported by data showing that the osmotic water permeability (Pf) for apical and/or basolateral cell membranes is sufficiently high to account for the transepithelial Pf, making a tentative conclusion for a transcellular route of water transport possible. In addition, measurements of Pf have yielded insights into the mechanism of solute-solvent coupling. Pf has been reported to be mostly between 0.1 and 0.3 cm/s. In the rabbit proximal straight and the Necturus proximal convoluted tubule, in which water transport rates are low, this range of Pf will account for volume absorption with only small osmotic gradients (less than 6 mosmol). Higher osmotic gradients are required in the rat and possibly the rabbit proximal convoluted tubule, where water transport rates are higher. Solute-solvent coupling in all species is probably due to both luminal hypotonicity and lateral intercellular space hypertonicity. These two processes are directly linked. Mass balance requires that generation of luminal hypotonicity also generates a hypertonic absorbate and, thus, some degree of lateral intercellular space hypertonicity. It is likely that, in the rabbit at least, effective osmotic pressure gradients due to differences in solute reflection coefficients play little role in solute-solvent coupling.

Osmolality, bicarbonate concentration, and water reabsorption in proximal tubule of the dog nephron

1963 ◽  
Vol 205 (2) ◽  
pp. 273-280 ◽  
Author(s):  
James R. Clapp ◽  
John F. Watson ◽  
Robert W. Berliner
Keyword(s):  
Plasma Concentration ◽  
Proximal Tubule ◽  
Proximal Convoluted Tubule ◽  
Water Reabsorption ◽  
Bicarbonate Concentration ◽  
Water Diuresis ◽  
Vasopressin Infusion ◽  
Proximal Tubular

Micropuncture and microanalytical techniques were used to study the effect of antidiuresis and water diuresis on osmolality, bicarbonate concentration, and water reabsorption in the proximal tubule of the dog nephron. Samples collected during antidiuresis and water diuresis remained isotonic to plasma throughout the first 50% of the proximal convoluted tubule. Mean bicarbonate concentrations of 16 mEq/liter and 17 mEq/liter were found in the middle third of the tubule during antidiuresis and water diuresis, respectively. These values were slightly less than the plasma concentration of 22 mEq/liter. Proximal tubular fluid samples for inulin concentration were collected during antidiuresis, water diuresis, and during vasopressin infusion in water-loaded dogs. A mean tubular fluid to plasma (TF/P) inulin ratio of 2.3 was found in the middle third of the proximal tubule during antidiuresis. This value is significantly different ( P < 0.01) from a mean of 1.6 in the same portion of the tubule during water diuresis. Vasopressin administration to hydrated dogs returned the TF/P inulin ratio in the middle third of the proximal tubule to 2.0. These results suggest that vasopressin stimulated Na reabsorption in the proximal tubule of the dog nephron.

Effect of hypermagnesemia on rat jejunal sodium and water transport

1976 ◽  
Vol 231 (6) ◽  
pp. 1771-1776 ◽  
Author(s):  
GF DiBona ◽  
LL Sawin
Keyword(s):  
Proximal Tubule ◽  
Water Transport ◽  
Renal Proximal Tubule ◽  
Epithelial Tissue ◽  
Rat Jejunum ◽  
Water Reabsorption ◽  
Sodium Influx ◽  
Sodium Efflux ◽  
Rat Renal Proximal Tubule

Hypermagnesemia decreases sodium and water reabsorption in the rat renal proximal tubule. To further understand this action, the effect of hypermagnesemia on sodium and water transport in the in vivo perfused rat jejunum was studied. The rat jejunum was chosen as another transporting epithelial tissue in the same species with unidirectional sodium flux characteristics similar to the rat renal proximal tubule, i.e., leaky as opposed to tight. Hypermagnesemia decreased net jejunal sodium and water reabsorption. This decrease was due to a reduction in unidirectional sodium efflux from lumen to blood and not to an increase in unidirectional sodium influx from blood to lumen. Hypermagnesemia did not change the jejunal permeability to inulin. The effect of hypermagnesemia on jejunal sodium and water transport is similar to that renal proximal tubule sodium and water transport. This similarity suggests that the mechanism of action of magnesium of these two transporting epithelial tissues is similar.

Nephron sites of action of nicotinamide on phosphate reabsorption

1984 ◽  
Vol 246 (1) ◽  
pp. F27-F31
Author(s):  
J. A. Haas ◽  
T. J. Berndt ◽  
A. Haramati ◽  
F. G. Knox
Keyword(s):  
Parathyroid Hormone ◽  
Proximal Tubule ◽  
Distal Tubule ◽  
Proximal Convoluted Tubule ◽  
Free Flow ◽  
Loop Of Henle ◽  
Phosphate Deprivation ◽  
Phosphate Reabsorption ◽  
Pars Recta ◽  
Sites Of Action

The administration of nicotinamide results in urinary phosphate excretions similar to those obtained with pharmacologic doses of parathyroid hormone (PTH). Free-flow micropuncture was performed to localize the nephron site(s) of inhibition of phosphate reabsorption by nicotinamide or PTH in thyroparathyroidectomized (TPTX) rats stabilized on a normal or low phosphate diet. In rats fed a normal phosphate diet phosphaturia was observed following either nicotinamide or PTH treatment. Nicotinamide inhibited phosphate reabsorption in the loop of Henle (pars recta) but not in the accessible proximal tubule. PTH inhibited phosphate reabsorption in both the accessible proximal tubule and the pars recta. In phosphate deprivation, the phosphaturic response to either nicotinamide or PTH was blunted. Although phosphate reabsorption was markedly inhibited in the accessible proximal tubule with both nicotinamide and PTH, subsequent reabsorption in the loop of Henle and distal tubule blunted the phosphaturia. We conclude that nicotinamide primarily inhibits phosphate reabsorption by the pars recta in rats fed a normal phosphate diet, whereas it inhibits phosphate reabsorption by the proximal convoluted tubule in rats fed a low phosphate diet. Furthermore, avid reabsorption of phosphate in the pars recta accounts for the resistance to the phosphaturic effect of nicotinamide or PTH seen in rats fed a low phosphate diet.

Hypocalcemia-associated modulation of renal response to acute volume expansion in rats

1987 ◽  
Vol 253 (4) ◽  
pp. F726-F733
Author(s):  
D. E. Wesson
Keyword(s):  
Body Weight ◽  
Proximal Tubule ◽  
Volume Expansion ◽  
Wistar Rats ◽  
Prostaglandin Synthesis ◽  
Free Flow ◽  
Renal Response ◽  
Clearance Studies ◽  
Chloride Excretion ◽  
Filtered Load

The present study used free-flow micropuncture and whole-kidney clearance studies to determine the renal response to normocalcemic vs. hypocalcemic acute volume expansion (AVE) in anesthetized Munich-Wistar rats. Animals received AVE with Ringer bicarbonate to 10% body weight; half of these animals were supplemented with calcium to maintain normocalcemia (VE + Ca2+) and half were allowed to become hypocalcemic (VE). Filtered load of chloride and total CO2 (TCO2) to the superficial proximal tubule and delivered load to the superficial loop segment were not different between groups. Superficial proximal tubule absolute Cl reabsorption was not different, but superficial loop segment absolute Cl reabsorption was less in the VE + Ca2+ animals (2,221+/- 106 vs. 2,651+/- 125 pmol/min, P less than 0.05) and whole-kidney fractional chloride excretion was greater (10.5+/- 1.6 vs. 4.3+/- 0.5%, P less than 0.05). When indomethacin (I) was administered to hypocalcemic (VE + I) and normocalcemic (VE + Ca2+ + I) AVE animals, both groups of animals had tubular and whole-kidney chloride reabsorption similar to VE animals. TCO2 reabsorption was not influenced by Ca2+ or I. The data indicate that normocalcemic vs. hypocalcemic AVE results in reduced superficial loop segment chloride reabsorption and greater whole-kidney fractional chloride excretion in the absence but not in the presence of prostaglandin inhibition. The data are compatible with an effect of hypocalcemia during AVE to limit superficial loop segment and whole-kidney chloride excretion by inhibiting renal prostaglandin synthesis.

D-Glucose enhancement of water reabsorption in proximal tubule of the rat kidney

1976 ◽  
Vol 231 (3) ◽  
pp. 777-780 ◽  
Author(s):  
EJ Weinman ◽  
WN Suki ◽  
G Eknoyan
Keyword(s):  
Proximal Tubule ◽  
Rat Kidney ◽  
Specific Effect ◽  
Proximal Convoluted Tubule ◽  
Water Reabsorption ◽  
Perfusion Solution ◽  
Tubular Lumen ◽  
Artificial Solution

Water reabsorption in the proximal convoluted tubule of the rat kidney was examined by in vivo microperfusion techniques in order to examine the effect of D-glucose within the tubular lumen. When tubules were perfused with a balanced artificial solution containing Na, K, Cl, HCO3, urea, and D-glucose, absolute reabsorption averaged 4.01 +/- 0.24 nl/min per mm. Addition of D-glucose to the NaCl perfusate enhanced water reabsorption to values similar to those obtained with the balanced artificial perfusate. The enhanced water reabsorption consequent to the addition of D-glucose to the NaCl perfusion solution was completely inhibited by addition of phloridzin to the perfusate. The addition of an unabsorbed hexose, 2-deoxy-D-glucose, to the NaCl perfusate failed to enhance water reabsorption, whereas the addition of an incompletely reabsorbed sugar that is not metabolized, 3-O-methyl-D-glucose, resulted in partial enhancement of theabsolute rate of water reabsorption. These studies demonstrate that D-glucose has the specific effect of augmenting water reabsorption in the proximal tubule of the rat kidney.

The early proximal tubule: a high-capacity delivery-responsive reabsorptive site

1987 ◽  
Vol 252 (4) ◽  
pp. F573-F584 ◽  
Author(s):  
D. A. Maddox ◽  
F. J. Gennari
Keyword(s):  
Proximal Tubule ◽  
High Capacity ◽  
Proximal Convoluted Tubule ◽  
Dynamic State ◽  
Transport Capacity ◽  
Load Dependence ◽  
Almost All ◽  
Early Proximal Tubule

The proximal convoluted tubule is responsible for reclaiming almost all of the filtered bicarbonate, glucose, and amino acids, as well as 40% or more of the filtered sodium, fluid, chloride, and phosphate. Walker and co-workers demonstrated the importance of this nephron segment as a high-capacity transport site in the first mammalian micropuncture studies, and they suggested that the first portion of the proximal tubule played a particularly important role in the ability of the nephron to adapt to variations in filtered load. Since then, many studies using micropuncture and in vivo and in vitro microperfusion techniques have confirmed that the early proximal tubule has a higher transport capacity than the late proximal tubule for a number of solutes. Moreover, at least for bicarbonate, fluid, and chloride, the transport capacity is not static, but is in a dynamic state, adapting in response to changes in filtration. In this review we have focused on the high capacity and load dependence of early proximal bicarbonate and fluid reabsorption. In addition, we summarize the evidence for axial heterogeneity along the proximal convoluted tubule for transport of a variety of other solutes.

Effects of acute alterations in PCO2 on proximal HCO-3, Cl-, and H2O reabsorption

1984 ◽  
Vol 246 (1) ◽  
pp. F21-F26 ◽  
Author(s):  
M. G. Cogan
Keyword(s):  
Sodium Transport ◽  
Wistar Rats ◽  
Proximal Convoluted Tubule ◽  
Free Flow ◽  
Arterial Pco2 ◽  
Nephron Segments ◽  
Bicarbonate Reabsorption ◽  
Juxtamedullary Nephron ◽  
Acute Changes ◽  
Significant Increment

The effect of acute changes in arterial PCO2 on absolute proximal reabsorption of bicarbonate, chloride, and water has not been systematically studied. In the present free-flow micropuncture studies in Munich-Wistar rats, arterial PCO2 was increased or decreased by 20 mmHg. Under conditions of stable SNGFR, proximal and whole kidney electrolyte reabsorption was measured. Acute hypocapnia decreased absolute proximal bicarbonate reabsorption by 23% (from 1,008 +/- 38 to 773 +/- 36 pmol/min). Proximal volume reabsorption also decreased. Although bicarbonate delivery out of the superficial proximal convoluted tubule did not exceed normal levels, bicarbonaturia developed, suggesting an additional suppression of acidification by distal and/or juxtamedullary nephron segments. Acute hypercapnia increased absolute proximal bicarbonate reabsorption by only 10% in chronically alkalotic animals (from 1,050 +/- 68 to 1,176 +/- 77 pmol/min). In acutely alkalotic animals, hypercapnia caused no significant increment in the higher basal level of absolute proximal bicarbonate reabsorption (from 1,158 +/- 120 to 1,234 +/- 97 pmol/min). Whole kidney bicarbonate reabsorption rose, again suggesting a distal and/or juxtamedullary effect. Hypercapnia inhibited proximal chloride reabsorption and caused a chloruresis. In conclusion, acute hypo- and hypercapnia caused alterations in proximal bicarbonate, chloride, and sodium transport that may participate, at least in part, in the changes in whole kidney electrolyte reabsorption observed in these conditions. Distal and/or juxtamedullary nephrons also appeared to contribute to the changes in renal acidification induced by alterations in systemic PCO2.

scholarly journals Angiotensin II stimulates trafficking of NHE3, NaPi2, and associated proteins into the proximal tubule microvilli

2010 ◽  
Vol 298 (1) ◽  
pp. F177-F186 ◽  
Author(s):  
Anne D. M. Riquier-Brison ◽  
Patrick K. K. Leong ◽  
Kaarina Pihakaski-Maunsbach ◽  
Alicia A. McDonough
Keyword(s):  
Angiotensin Ii ◽  
Proximal Tubule ◽  
Flow Rate ◽  
Enzyme Inhibitor ◽  
Volume Flow Rate ◽  
Ang Ii ◽  
Sprague Dawley ◽  
Water Reabsorption ◽  
Associated Proteins ◽  
Gradient Fractionation

Angiotensin II (ANG II) stimulates proximal tubule (PT) sodium and water reabsorption. We showed that treating rats acutely with the angiotensin-converting enzyme inhibitor captopril decreases PT salt and water reabsorption and provokes rapid redistribution of the Na+/H+ exchanger isoform 3 (NHE3), Na+/Pi cotransporter 2 (NaPi2), and associated proteins out of the microvilli. The aim of the present study was to determine whether acute ANG II infusion increases the abundance of PT NHE3, NaPi2, and associated proteins in the microvilli available for reabsorbing NaCl. Male Sprague-Dawley rats were infused with a dose of captopril (12 μg/min for 20 min) that increased PT flow rate ∼20% with no change in blood pressure (BP) or glomerular filtration rate (GFR). When ANG II (20 ng·kg−1·min−1 for 20 min) was added to the captopril infusate, PT volume flow rate returned to baseline without changing BP or GFR. After captopril, NHE3 was localized to the base of the microvilli and NaPi2 to subapical cytoplasmic vesicles; after 20 min ANG II, both NHE3 and NaPi2 redistributed into the microvilli, assayed by confocal microscopy and density gradient fractionation. Additional PT proteins that redistributed into low-density microvilli-enriched membranes in response to ANG II included myosin VI, DPPIV, NHERF-1, ezrin, megalin, vacuolar H+-ATPase, aminopeptidase N, and clathrin. In summary, in response to 20 min ANG II in the absence of a change in BP or GFR, multiple proteins traffic into the PT brush-border microvilli where they likely contribute to the rapid increase in PT salt and water reabsorption.

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