Distal perfusion studies: transport stimulation by native tubule fluid

1990 ◽  
Vol 258 (6) ◽  
pp. F1523-F1527 ◽  
Author(s):  
G. Malnic ◽  
R. W. Berliner ◽  
G. Giebisch
Keyword(s):  
Proximal Tubule ◽  
Distal Tubule ◽  
Free Flow ◽  
Flow Conditions ◽  
Perfusion Studies ◽  
Potassium Secretion ◽  
Series Of Experiments ◽  
Distal Tubules ◽  
Distal Perfusion ◽  
Tubule Fluid

It is well established that potassium secretion into the distal tubule increases with the rate of flow. In a previous study [G. Malnic, R. W. Berliner, and G. Giebisch. Am. J. Physiol. 256 (Renal Fluid Electrolyte Physiol. 25): F932-F1271, 1989] we found that the increase with the rate of perfusion with a fluid made up to resemble that normally found in the early distal tubule was substantially less than the increase in free-flow conditions [R. N. Khuri, M. Wiederholt, N. Strieder, and G. Giebisch. Am. J. Physiol. 228: 1249–1261, 1975]. Because of the possibility that some important component was missing from the artificial fluid, we have carried out another series of experiments in which distal tubules were perfused with fluid collected from late proximal tubules and compared the results with those obtained when tubules were perfused with an artificial fluid with an electrolyte composition similar to that of late proximal fluid. When proximal tubule fluid was used, the potassium concentrations in the collected distal fluid were higher and better maintained with increasing flow than when the artificial fluid was used, and consequently the rate of potassium secretion was substantially greater with the proximal tubule fluid, approaching the results of previous studies in free flow. The nature of the component missing from the artificial solution is not known.

Chloride-dependent potassium secretion in early and late renal distal tubules

1987 ◽  
Vol 253 (3) ◽  
pp. F555-F562 ◽  
Author(s):  
H. Velazquez ◽  
D. H. Ellison ◽  
F. S. Wright
Keyword(s):  
Interstitial Fluid ◽  
Diffusion Mechanism ◽  
Chloride Concentration ◽  
Distal Tubule ◽  
Distal Segment ◽  
Collecting Tubule ◽  
Potassium Secretion ◽  
Series Of Experiments ◽  
Distal Tubules

Potassium transport by subsegments of the rat surface distal tubule was studied using a modified in vivo microperfusion method. The nephron segments between 14 and 38% and between 62 and 83% of total distal length distance between macula densa region and confluence of tubule with another) were perfused separately. The first of these two segments is composed primarily of distal convoluted tubule (DCT) cells; the more distal segment is made up primarily by initial collecting tubule (ICT) epithelium. Experiments were performed to measure potassium secretion via two pathways: a diffusion mechanism driven by a favorable electrochemical gradient for potassium, and a cotransport mechanism activated when lumen chloride concentration is low. In a first series of experiments, both the DCT and the ICT secreted potassium when perfused with an artificial control solution resembling fluid normally present at the beginning of the distal tubule. Absolute rates of potassium secretion were higher in the ICT than in the DCT. Decreasing lumen Cl concentration stimulated potassium secretion more in the ICT than in the DCT. In a second series of experiments, the subsegments were perfused with a solution in which ion concentrations were raised to levels found in interstitial fluid. Under these circumstances, potassium secretion was lower in both segments. Decreasing lumen Cl concentration resulted in higher rates of potassium secretion in the DCT than those seen in the first series with low chloride; rates of potassium secretion in the ICT were as high as in the first series.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of pH on potassium transport by renal distal tubule

1982 ◽  
Vol 242 (5) ◽  
pp. F544-F551 ◽  
Author(s):  
B. A. Stanton ◽  
G. Giebisch
Keyword(s):  
Metabolic Acidosis ◽  
Distal Tubule ◽  
Potassium Transport ◽  
Free Flow ◽  
Acid Base Balance ◽  
Acid Base ◽  
Solution Ph ◽  
Fluid Delivery ◽  
Urinary Potassium ◽  
Potassium Secretion

To determine the relative importance of plasma and luminal pH changes as factors regulating potassium secretion by rat distal tubule, superficial tubules were continuously microperfused in vivo. The effects of changes in plasma pH were examined by producing acute systemic metabolic acidosis or alkalosis and holding luminal flow rate, solute composition, and pH constant by microperfusion. Alternatively, the effect of luminal solution pH was evaluated by microperfusing tubules with solutions buffered to either pH 6.5 or 8.0 at constant systemic acid-base balance. Net transport of Na and K and the pH of the luminal fluid were measured. Results showed that metabolic acidosis inhibited and metabolic alkalosis stimulated potassium secretion. Increased luminal fluid pH, in contrast, did not stimulate potassium transport. In experiments in which metabolic acidosis produced a diuresis, urinary potassium excretion was enhanced compared with hydropenic controls. Free-flow micropuncture studies revealed that the rate of fluid delivery to the distal tubule was 45% greater during acidosis compared with control and that potassium secretion increased in both the distal and collecting tubule. Since the rate of fluid delivery is a potent stimulus of potassium secretion in the distal tubule, it is concluded that the stimulus of increased delivery of fluid, observed in free-flow conditions, masked the inhibitory effect of acidosis on potassium transport. Potassium transport by the distal tubule, during acid-base disorders, is regulated by plasma pH and the rate of delivery of fluid but is not stimulated by alkalinization of the luminal fluid.

Stimulation of distal potassium secretion by low lumen chloride in the presence of barium

1985 ◽  
Vol 248 (5) ◽  
pp. F638-F649 ◽  
Author(s):  
D. H. Ellison ◽  
H. Velazquez ◽  
F. S. Wright
Keyword(s):  
Chloride Concentration ◽  
Distal Tubule ◽  
Perfusion Fluid ◽  
Transport Pathway ◽  
Luminal Membrane ◽  
Potassium Secretion ◽  
Transepithelial Voltage ◽  
Tubule Fluid ◽  
Stimulation Of

Potassium secretion into the renal distal tubule is increased when chloride in the tubule fluid is replaced by another anion. The present experiments were done to determine whether this increment in transported potassium traverses a conductive pathway from cell to lumen. Transport rates of potassium, sodium, chloride, and fluid by the renal distal tubule of rats were examined in vivo by continuous microperfusion. The effects of substituting gluconate for chloride in the presence and absence of 5 mM barium in the perfusion fluid were determined. When gluconate replaced chloride in the perfusion solutions, potassium secretion increased (by 44%) without a significant change in transepithelial voltage. Barium in the lumen increased the magnitude of the lumen-negative transepithelial voltage (by 30%) and reduced potassium secretion (by 56%) by inhibiting conductive potassium movement. Barium also decreased both sodium (by 51%) and chloride (by 37%) absorption. Barium did not reduce the stimulation of potassium secretion caused by reducing lumen chloride concentration. Potassium secretion increased (by 77%) when lumen chloride was reduced in the presence of 5 mM barium. We interpret these results by postulating that a cotransport mechanism linking potassium and chloride is present in the luminal membrane of distal tubule cells, that this mechanism operates in parallel with a conductive transport pathway for potassium, and that the K-Cl cotransport mechanism is not inhibited by barium.

Tubular Handling of Phosphate along the Nephron of Thyroparathyroidectomized Rats Injected with Ethane-1-Hydroxy-1,1-Diphosphonate

1981 ◽  
Vol 60 (2) ◽  
pp. 171-177 ◽  
Author(s):  
R. C. Mühlbauer ◽  
J.-P. Bonjour ◽  
H. Fleisch
Keyword(s):  
Proximal Tubule ◽  
Bone Mineral ◽  
Adaptive Response ◽  
Distal Tubule ◽  
Tubular Reabsorption ◽  
Free Flow ◽  
Induced Changes ◽  
Terminal Nephron ◽  
Early Proximal Tubule

1. Previous studies have shown that in thyroparathyroidectomized rats injection of disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP) at doses that inhibit bone mineral retention (0.16 mmol = 10 mg of phosphorus/kg body wt. per day subcutaneously) leads to a decrease in the net tubular reabsorption of phosphate. 2. In the present work the tubular response to EHDP (0.16 mmol/kg body wt.) injected subcutaneously for 9 days has been localized by free-flow micropuncture in thyroparathyroidectomized rats. 3. The results show that the net tubular reabsorption of phosphate along the first portion of the (early) proximal tubule was markedly depressed in the EHDP-injected thyroparathyroidectomized rats compared with that in the pair-fed thyroparathyroidectomized control animals. In this latter group the delivery of phosphate to the distal tubule was larger than in the final urine, confirming previous reports. In the EHDP-injected thyroparathyroidectomized rats no difference in delivery of phosphate was found between the distal tubule and the final urine, suggesting that diphosphonate inhibited net reabsorption of phosphate in the terminal nephron. 4. The sites of the EHDP-induced changes in the tubular handling of phosphate were similar to those previously determined for the adaptive response to an increase in the supply of phosphate.

High affinity Ca2+–Mg2+ ATPase in the distal tubule of the mouse kidney

1987 ◽  
Vol 65 (10) ◽  
pp. 2093-2098 ◽  
Author(s):  
Michèle G. Brunette ◽  
Sylvie Blouin ◽  
Meathan Chan
Keyword(s):  
Proximal Tubule ◽  
Kinetic Parameters ◽  
Atp Hydrolysis ◽  
Limit Of Detection ◽  
Distal Tubule ◽  
Mouse Kidney ◽  
Distal Nephron ◽  
Low Concentrations ◽  
Distal Tubules ◽  
Shed Light

The purpose of this study was to investigate whether Ca2+–Mg2+ ATPase in the distal tubule (where calcium transport is active, against a gradient, and hormone dependent) presents some characteristics different from those observed in the proximal tubule, and whether these characteristics are likely to shed light on the respective roles of this enzyme at the two sites of the nephron. The Ca2+- and Mg2+-dependent ATP hydrolysis was measured in microdissected segments of the distal nephron, the kinetic parameters were determined, and the influence of magnesium upon the sensitivity to calcium was examined. Results were compared with those obtained in the proximal tubule, and in purified membranes as reported by others. In the distal tubule, low concentrations of Mg2+ (< 10−7 M) did not influence ATP hydrolysis. At concentrations above 10−7 M, Mg2+ increased ATP hydrolysis according to Michaelis kinetics (apparent Km = 11.3 ± 2.4 μM, Vmax = 219 ± 26 pmol∙mm−1∙20 min−1). The addition of 1 μM Ca2+ decreased the apparent Km for Mg2+ and the Vmax for Mg2+. Similar results were obtained in the proximal tubule. At low Mg2+ concentrations, Ca2+ also stimulated ATP hydrolysis according to Michaelis kinetics with an apparent Km value for Ca2+ of 0.18 ± 0.06 and 0.10 ± 0.03 μM Ca2+ (ns) and a Vmax of 101 ± 12 and 89 ± 9 pmol∙mm−1∙20 min−1 (ns) in the distal and proximal tubules, respectively. In the two segments, the addition of Mg2+ strongly decreased the sensitivity to 1 μM Ca2+ so that at 1 mM Mg2+, the Ca2+-dependent ATPase activity was at the limit of detection. In conclusion, the kinetic parameters of the Ca2+- and Mg2+-dependent ATP hydrolysis were similar at the two sites of the nephron, and were also similar to those reported for the enzyme present in purified basolateral membranes. The nonadditive effect of the two cations Ca2+ and Mg2+ suggests that the two ATPase activities belong to the same enzyme, and this enzyme is the same in the proximal and distal tubules. Differences in Ca2+ transport characteristics should be attributed to factors other than variations in the nature of the Ca2+–Mg2+ ATPase.

scholarly journals Effect of propranolol on phosphate reabsorption by superficial nephron segments in response to parathyroid hormone in phosphate-deprived rats.

1990 ◽  
Vol 1 (2) ◽  
pp. 200-204
Author(s):  
A Rybczynska ◽  
A Hoppe ◽  
F G Knox
Keyword(s):  
Parathyroid Hormone ◽  
Proximal Tubule ◽  
Distal Tubule ◽  
Free Flow ◽  
Phosphate Deprivation ◽  
Phosphate Reabsorption ◽  
Nephron Segments ◽  
Pars Recta

Phosphate deprivation causes a resistance to the phosphaturic effect of parathyroid hormone. The decreased phosphaturic response to parathyroid hormone in rats fed a low phosphate diet for 1 day can be restored by propranolol infusion. Free-flow micropuncture studies were performed to localize the nephron site of restoration of the phosphaturic effect of parathyroid hormone by propranolol in rats deprived of phosphate for one day. In animals fed low phosphate diet and in the presence of parathyroid hormone, propranolol infusion did not change phosphate delivery to the late proximal tubule; however, fractional delivery of phosphate to the early distal tubule was significantly increased from 18.3 +/- 2.9 to 32.2 +/- 4.1%. In rats fed a normal phosphate diet, propranolol infusion did not change phosphate delivery along the nephron. We conclude that the restoration of the phosphaturic effect of parathyroid hormone by propranolol infusion in rats deprived of phosphate for 1 day is primarily due to decreased reabsorption of phosphate by superficial loop segments, most likely the pars recta segment of the proximal tubule.

scholarly journals Endopeptidases (kininases) are able to hydrolyze kinins in tubular fluid along the rat nephron

1999 ◽  
Vol 277 (1) ◽  
pp. F66-F74 ◽  
Author(s):  
D. E. Casarini ◽  
M. A. Boim ◽  
R. C. R. Stella ◽  
N. Schor
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Proximal Tubule ◽  
Physiological Role ◽  
Distal Tubule ◽  
Neutral Endopeptidase ◽  
Prolyl Endopeptidase ◽  
Proximal Tubules ◽  
Converting Enzyme ◽  
Distal Nephron ◽  
Distal Tubules

The activities of serine endopeptidase, prolyl endopeptidase and neutral endopeptidase were determined in tubular fluid collected from several portions of the rat nephron as well as in urine. The enzyme activities were measured by HPLC using bradykinin (BK) as substrate. Free residual peptides of BK obtained by the action of these enzymes on the locally produced BK were also determined. The endopeptidase activities were found to be present throughout the nephron. Equimolar fragments of BK were detected in the early proximal tubule (Arg1-Pro7, Phe8-Arg9, Arg1-Gly4, Phe5-Arg9, and BK), late proximal tubule (Arg1-Phe5, Arg1-Pro7, Gly4-Pro7, Gly4-Arg9, and BK), late distal tubule (Arg1-Gly4, Phe5-Arg9, Arg1-Phe5, Ser6-Arg9, Gly4-Arg9, BK, and [des-Arg9]BK) and urine (Phe8-Arg9, Phe5-Arg9, Arg1-Phe5, Ser6-Arg9, Arg1-Pro7, Gly4-Pro7, Gly4-Arg9, BK, and [des-Arg9]BK). Our data suggest that the endopeptidases and exopeptidases are secreted by the nephron. Early proximal tubules secrete angiotensin converting enzyme and neutral endopeptidase, differing from late distal tubules that produce prolyl endopeptidase, serine endopeptidase, carboxypeptidase, and also neutral endopeptidase. All enzymes detected along the rat nephron were found in the urine. The existence of endopeptidases and carboxypeptidase in the distal nephron may have a potential physiological role in the inactivation of the kinins formed by kallikrein in the kidney and also in the inactivation of additional peptides other than BK.

Luminal influences on potassium secretion: low sodium concentration

1984 ◽  
Vol 246 (5) ◽  
pp. F609-F619 ◽  
Author(s):  
D. W. Good ◽  
H. Velazquez ◽  
F. S. Wright
Keyword(s):  
Driving Forces ◽  
Sodium Concentration ◽  
Perfusion Fluid ◽  
Low Sodium ◽  
K Secretion ◽  
Potassium Secretion ◽  
Transepithelial Voltage ◽  
Series Of Experiments ◽  
Distal Tubules

In vivo microperfusion techniques were employed in anesthetized rats to determine whether K secretion by renal distal tubules requires the presence of Na in luminal fluid, and, if it does, in what concentration range do changes in Na concentration have the most effect. In a first series of experiments Na in perfusion fluid was replaced at constant Cl with tetramethylammonium (TMA). When the perfusion fluid Na concentration was reduced from 96 or 34 mM to 10 or 3 mM, K secretion was reduced by 50-60% and transepithelial voltage ( VTE ) was reduced by 40-60%. In a second series of experiments, in which NaCl was replaced with urea, perfusion fluid Na concentration again was reduced to 3 mM, and K secretion and VTE were reduced. In a third series of experiments, Na was replaced with rubidium. The reduced K secretion could not be explained solely by changes in electrical driving forces. The results indicate that some luminal Na (half-maximal concentration approx 10 mM) is necessary to permit K secretion to proceed at a normal rate. Considering prior measurements of luminal Na concentration in rat distal tubules, it is unlikely that changes in luminal Na concentration play an important role in regulating the rate of distal K secretion.

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.

Localization of Diuretic Action of Chlormerodrin in the Nephron of the Dog

1958 ◽  
Vol 194 (3) ◽  
pp. 540-546 ◽  
Author(s):  
R. H. Kessler ◽  
K. Hierholzer ◽  
R. S. Gurd ◽  
R. F. Pitts
Keyword(s):  
Proximal Tubule ◽  
Active Transport ◽  
Distal Tubule ◽  
Chloride Ions ◽  
Flow Conditions ◽  
Flow Method ◽  
Diuretic Action ◽  
Partial Inhibition ◽  
Equivalent Reduction ◽  
Stop Flow

The stop flow method of Malvin, Sullivan and Wilde ( Physiologist 1:58, 1957) has been applied in a study to localize the diuretic action of chlormerodrin in the nephron of the dog. It has been observed that under stop flow conditions, chlormerodrin reduces both the U/P ratio for creatinine in the proximal tubule and the gradient against which the proximal tubule can reabsorb sodium and chloride ions. These results are interpreted as indicating partial inhibition of active transport of sodium and/or chloride ions in the proximal segment of the nephron and equivalent reduction in the osmotic back flow of water. The reabsorption of sodium and/or chloride ions is inhibited in the same portion of the tubule which secretes the diuretic and which secretes p-aminohippurate. These experiments provide no evidence for inhibition of reabsorption of sodium of sodium and chloride ions by chlormerodrin in the distal tubule.

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