Localization of diuretic action in microperfused rat distal tubules: Ca and Na transport

1985 ◽  
Vol 248 (4) ◽  
pp. F527-F535 ◽  
Author(s):  
L. S. Costanzo
Keyword(s):  
Distal Tubule ◽  
Maximal Concentration ◽  
Na Transport ◽  
Tubule Cell ◽  
Ca Transport ◽  
Site Of Action ◽  
Distal Tubules ◽  
Sites Of Action ◽  
Distal Site

Experiments were performed in rats to examine the distal site of action of thiazide diuretics and the additive hypocalciuric properties of thiazides and amiloride. In clearance experiments, the maximal natriuretic and hypocalciuric dose of chlorothiazide was established. When amiloride was added, there was further augmentation of Ca reabsorption (P less than 0.025) but no additional natriuresis. Amiloride blunted thiazide-induced kaliuresis (P less than 0.001). Localization of the thiazide effect was studied in early and late distal tubules microperfused in vivo with control and thiazide-containing solutions. The maximally effective luminal drug concentration, 5 X 10(-4) M, inhibited Na transport (P less than 0.001) and enhanced Ca transport (P less than 0.01) in the early distal segments; late segments were on the average unaffected. It is suggested that thiazides interact with the distal convoluted tubule cell, whose predominant location is the early distal tubule. In two long distal tubules, with early and late segments, a maximal concentration of chlorothiazide increased Ca transport and decreased Na transport. Addition of 10(-5) M amiloride caused an additional increment in Ca reabsorption. As amiloride's action is located in the late distal tubule, it is suggested from these experiments that a basis for additive hypocalciuric actions of thiazides and amiloride is separate sites of action in the distal tubule.

Comparison of calcium and sodium transport in early and late rat distal tubules: effect of amiloride

1984 ◽  
Vol 246 (6) ◽  
pp. F937-F945 ◽  
Author(s):  
L. S. Costanzo
Keyword(s):  
Distal Tubule ◽  
Clearance Ratio ◽  
Membrane Hyperpolarization ◽  
Ca Transport ◽  
Luminal Membrane ◽  
Osmotic Water ◽  
Distal Tubules ◽  
Highly Correlated ◽  
Convoluted Tubules

In vivo tubular microperfusion experiments were performed in rats to compare the function of the early and late rat distal convoluted tubule and to examine the effect of amiloride on distal Na and Ca reabsorption. In clearance experiments, amiloride (6 micrograms/min) reduced fractional Ca excretion (P less than 0.05) and the calcium-to-sodium clearance ratio (P less than 0.001) without affecting fractional Na excretion. The in vivo microperfusion experiments revealed a higher rate of osmotic water flow in late distal convoluted tubules than in early tubules (P less than 0.001), while Na and Ca transport rates were comparable. The addition of 10(-5) M amiloride to the luminal perfusate inhibited net fluid reabsorption (P less than 0.05) and Na reabsorption (P less than 0.01) and enhanced Ca reabsorption (P less than 0.005) in late segments of the distal tubule. The drug did not change early distal function. The degree of enhancement of Ca transport was highly correlated with the degree of inhibition of Na transport, suggesting that the two effects are related. We suggest that increased Ca reabsorption is a result of luminal membrane hyperpolarization or of increased rates of Ca-Na exchange.

Active potassium absorption by the renal distal tubule

1992 ◽  
Vol 262 (3) ◽  
pp. F488-F493 ◽  
Author(s):  
M. D. Okusa ◽  
R. J. Unwin ◽  
H. Velazquez ◽  
G. Giebisch ◽  
F. S. Wright
Keyword(s):  
Distal Tubule ◽  
Sprague Dawley ◽  
Direct Demonstration ◽  
Sprague Dawley Rats ◽  
Potassium Flux ◽  
Low Potassium ◽  
Potassium Absorption ◽  
Transepithelial Voltage ◽  
Distal Tubules

Maintenance of potassium homeostasis during potassium depletion appears to involve an active potassium absorptive mechanism in the distal nephron. Direct demonstration of such a pathway in the distal tubule of the rat has been lacking. The purpose of the current study was to examine the hypothesis that an ATP-dependent active transport mechanism plays a role in potassium absorption by the rat distal tubule. We utilized in vivo microperfusion techniques in Sprague-Dawley rats maintained on a regular diet of low-potassium diet for 3-4 wk. The effect of a selective inhibitor of the gastric H-K-adenosinetriphosphatase (ATPase) (Sch 28080, 0.1 mM) was tested in distal tubules of both groups of rats. Distal tubules of normal rats secreted potassium. Sch 28080 had no effect on this net potassium flux. In contrast, distal tubules of potassium-deficient rats absorbed potassium. Sch 28080 abolished this potassium absorption and produced a small hyperpolarization of the lumen-negative transepithelial voltage (VTE). The change in VTE can be explained by a concomitant increase in potassium concentration in the late distal tubule. These results are consistent with the presence of an H-K-ATPase in the distal tubule of potassium-deficient rats.

Distal tubular acidification in the remnant kidney

1990 ◽  
Vol 258 (1) ◽  
pp. F69-F74 ◽  
Author(s):  
R. T. Kunau ◽  
K. A. Walker
Keyword(s):  
Distal Tubule ◽  
Relative Increase ◽  
Control Group ◽  
Acid Base ◽  
Urine Ph ◽  
Base Parameters ◽  
Distal Tubules ◽  
The Difference ◽  
Remnant Kidney

The present studies examined the effect of three-fourths nephrectomy on the rate of acidification, i.e., total CO2 (tCO2) absorption (JtCO2) in the superficial distal tubule of the rat. Total glomerular filtration rate following three-fourths nephrectomy was 1.29 +/- 0.06 vs. 3.29 +/- 0.08 ml/min in sham controls, P less than 0.001. Systemic acid-base parameters were the same in both groups, but urine pH was lower in nephrectomized rats. In vivo microperfusion with identical isohydric solutions revealed that the JtCO2, fluid absorption (Jv), lumen-negative transepithelial potential difference (VT) were all significantly greater in the distal tubule of remnant kidneys. As the relative increase in Jv exceeded JtCO2, the perfusate tCO2 concentration increased markedly in remnant kidney distal tubules from 30.3 +/- 0.59 to 39.9 +/- 1.73 mM. To determine if the increase in tCO2 concentration accounted for the difference in JtCO2, a second control group was studied using a perfusate tCO2 concentration of 39.6 +/- 0.79 mM. Distal tubular JtCO2, Jv, and VT were significantly less in this control group than in the remnant kidney group. In separate studies, 10(-4) M amiloride was added to the perfusate used in remnant kidneys and controls studied with the elevated perfusate tCO2 concentration. The addition of 10(-4) M amiloride to the perfusate reduced VT and JtCO2. At identical values for VT, JtCO2 was higher in the distal tubule of remnant kidneys than in controls. We conclude the following. 1) The rate of acidification is increased in the distal tubule of remnant kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo adaptation of bicarbonate reabsorption by rat distal tubules during acid loading

1994 ◽  
Vol 267 (5) ◽  
pp. F737-F747 ◽  
Author(s):  
D. Z. Levine ◽  
M. Iacovitti ◽  
S. Buckman ◽  
D. Vandorpe ◽  
V. Harrison ◽  
...  
Keyword(s):  
Water Flux ◽  
Distal Tubule ◽  
Bafilomycin A1 ◽  
Bicarbonate Reabsorption ◽  
Distal Tubules ◽  
Acid Loading ◽  
Fasted Rats ◽  
Predominant Effect ◽  
Stimulation Of

We carried out in vivo microperfusion experiments in acid-loaded rats to characterize the adaptive response of the unidirectional components secretory flux (Jsec) and reabsorptive flux (Jreab)] of distal tubule bicarbonate reabsorption and to test the hypothesis that Jreab is dependent on bafilomycin A1-sensitive H(+)-adenosinetriphosphatase activity. During 18 h of severe acidosis there was a significant decrease in Jsec (-15 +/- 3 vs. -38 +/- 5 pmol.min-1.mm-1, P < 0.05) and a significant increase in Jreab (37 +/- 6 vs. 0 +/- 5 pmol.min-1.mm-1, P < 0.05), which was insensitive to 10(-5) M bafilomycin A1, 10(-5) M Sch-28080, and 3 mM amiloride. After 3 days of acid loading, these same inhibitors reduced Jreab by approximately 60%. However, when water flux was completely inhibited by isosmotic perfusion, a significant Jreab (15 +/- 2 pmol.min-1.mm-1) resistant to 10(-5) M bafilomycin A1 persisted, as in severe acidosis. In reabsorbing distal tubules of overnight-fasted rats, Sch-28080 elicited no inhibition, whereas bafilomycin A1 and amiloride had significant effects (28 +/- 5, 24 +/- 4, respectively, vs. 50 +/- 4 pmol.min-1.mm-1 for fasted rats, P < 0.05). Thus, although Jsec is reduced in the transition from mild to severe metabolic acidosis of 18-h duration, the predominant effect is a stimulation of bafilomycin A1-resistant Jreab.

In vivo modulation of rat distal tubule net HCO3 flux by VIP, isoproterenol, angiotensin II, and ADH

1994 ◽  
Vol 266 (6) ◽  
pp. F878-F883 ◽  
Author(s):  
D. Z. Levine ◽  
M. Iacovitti ◽  
S. Buckman ◽  
V. Harrison
Keyword(s):  
Angiotensin Ii ◽  
Vasoactive Intestinal Peptide ◽  
Distal Tubule ◽  
Similar Response ◽  
Acid Base Balance ◽  
Base Balance ◽  
Distal Tubules ◽  
In Vivo Effects ◽  
Fasted Rats

To examine the in vivo effects of agonists reported to influence bicarbonate flux (JtCO2), microperfusion experiments were carried out on distal tubules of normally fed or overnight-fasted rats. As we previously reported, distal tubules from fed rats reabsorbed no bicarbonate, whereas overnight-fasted rats consistently reabsorbed bicarbonate (JtCO2 10 +/- 3 pmol.min-1.mm-1; P < 0.01). Vasoactive intestinal peptide and isoproterenol infused intravenously (7.3 and 4.0 micrograms.kg-1.h-1, respectively) in fasted rats suppressed JtCO2 and, in the case of vasoactive intestinal peptide, elicited net bicarbonate secretion (JtCO2 -10 +/- 2 and -4 +/- 4 pmol.min-1.mm-1, respectively). In fed rats, angiotensin II infused at a rate of 1.2 micrograms.kg-1.h-1 stimulated bicarbonate reabsorption (JtCO2 16 +/- 3 pmol.min-1.mm-1), while antidiuretic hormone infused at 0.024 micrograms.kg-1.h-1 elicited a similar response (17 +/- 4 pmol.min-1.mm-1), both values being significantly different from control. These results, therefore, demonstrate for the first time that these agonists can modulate JtCO2 at the distal tubule site in vivo and therefore may be potential regulators of systemic acid-base balance.

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)

Augmented bidirectional HCO3 transport by rat distal tubules in chronic alkalosis

1991 ◽  
Vol 261 (2) ◽  
pp. F308-F317 ◽  
Author(s):  
D. E. Wesson ◽  
G. M. Dolson
Keyword(s):  
Metabolic Alkalosis ◽  
Distal Tubule ◽  
Free Flow ◽  
Proton Secretion ◽  
Nephron Segment ◽  
Distal Tubules ◽  
And Control

Free-flow micropuncture studies show both augmented net HCO3 reabsorption in the distal tubule of rats with chronic metabolic alkalosis and higher HCO3 delivery to this nephron segment. The present studies in rats used in vivo microperfusion of surface distal tubules to investigate whether the augmented net reabsorption 1) was due to decreased HCO3 secretion and/or to increased proton secretion or 2) depended on the higher HCO3 delivery to the distal tubule. Artificial perfusates were designed to simulate in situ deliveries of HCO3 to the distal tubules of both alkalotic and control animals and to represent extremes of in situ Cl deliveries. Rather than being decreased, both measured and calculated HCO3 secretion were higher in the alkalotic animals for each perfusate used. Similarly, calculated proton secretion (difference between net HCO3 reabsorption and calculated HCO3 secretion) was higher for the alkalotic animals using each HCO3-containing perfusate. Augmented net HCO3 reabsorption by alkalotic animals was more clearly demonstrated using higher HCO3 deliveries and Cl-free perfusates. These studies demonstrate that both the reabsorptive and secretory components of net HCO3 transport are increased in the distal tubule of animals with chronic metabolic alkalosis.

Endothelin-1 increases rat distal tubule acidification in vivo

1997 ◽  
Vol 273 (4) ◽  
pp. F586-F594 ◽  
Author(s):  
Donald E. Wesson ◽  
George M. Dolson
Keyword(s):  
Distal Tubule ◽  
Endothelin Receptor ◽  
Endothelin 1 ◽  
Anesthetized Rats ◽  
Receptor Inhibition ◽  
Dietary Acid ◽  
Distal Tubules ◽  
Do So

Because endothelin receptor inhibition blunts increased distal tubule acidification induced by dietary acid, we examined whether endothelin-1 (ET-1) increases acidification of in vivo perfused distal tubules of anesthetized rats. ET-1 was infused intra-aortically (1.4 pmol ⋅ kg−1 ⋅ min−1) into control animals and into those with increased distal tubule HCO3 secretion induced by drinking 80 mM NaHCO3 solution for 7–10 days. ET-1 increased distal tubule acidification in both control and NaHCO3 animals. Increased acidification in control animals was mediated by increased distal tubule H+ secretion (23.7 ± 2.2 vs. 18.7 ± 1.7 pmol ⋅ mm−1 ⋅ min−1, P < 0.05) with no changes in HCO3 secretion. By contrast, ET-1 increased distal tubule acidification in NaHCO3 animals predominantly by decreasing HCO3 secretion (−9.5 ± 1.0 vs. −18.7 ± 1.8 pmol ⋅ mm−1 ⋅ min−1, P < 0.001) with less influence on H+ secretion. When indomethacin was infused (83 μg ⋅ kg−1 ⋅ min−1) to inhibit synthesis of prostacyclin, an agent previously shown to increase HCO3 secretion in the distal tubule, ET-1 increased distal tubule H+ secretion in both control (24.3 ± 2.2 vs. 15.7 ± 1.6 pmol ⋅ mm−1 ⋅ min−1, P < 0.02) and NaHCO3 (20.0 ± 2.0 vs. 13.6 ± 1.4 pmol ⋅ mm−1 ⋅ min−1, P < 0.05) without affecting HCO3 secretion. The data show that ET-1 increases distal tubule acidification in vivo and can do so by increasing H+ secretion and by decreasing HCO3 secretion when the latter is augmented by dietary NaHCO3.

Effect of uroguanylin on potassium and bicarbonate transport in rat renal tubules

2006 ◽  
Vol 84 (10) ◽  
pp. 1003-1010 ◽  
Author(s):  
José Benedito Oliveira Amorim ◽  
Raif Musa-Aziz ◽  
Lucilia M.A. Lessa ◽  
Gerhard Malnic ◽  
Manassés Claudino Fonteles
Keyword(s):  
Rat Kidney ◽  
Distal Tubule ◽  
Bicarbonate Transport ◽  
Control Group ◽  
Renal Tubules ◽  
Stationary Concentration ◽  
K Channels ◽  
Series Of Experiments ◽  
Distal Tubules

The effect of uroguanylin (UGN) on K+ and H+ secretion in the renal tubules of the rat kidney was studied using in vivo stationary microperfusion. For the study of K+ secretion, a tubule was punctured to inject a column of FDC-green-colored Ringer's solution with 0.5 mmol KCl/L ± 10−6 mol UGN/L, and oil was used to block fluid flow. K+ activity and transepithelial potential differences (PD) were measured with double microelectrodes (K+ ion-selective resin vs. reference) in the distal tubules of the same nephron. During perfusion, K+ activity rose exponentially, from 0.5 mmol/L to stationary concentration, allowing for the calculation of K+ secretion (JK). JK increased from 0.63 ± 0.06 nmol·cm–2·s–1 in the control group to 0.85 ± 0.06 in the UGN group (p < 0.01). PD was –51.0 ± 5.3 mV in the control group and –50.3 ± 4.98 mV in the UGN group. In the presence of 10−7 mol iberiotoxin/L, the UGN effect was abolished: JK was 0.37 ± 0.038 nmol·cm–2·s–1 in the absence of, and 0.38 ± 0.025 in the presence of, UGN, indicating its action on maxi-K channels. In another series of experiments, renal tubule acidification was studied, using a similar method: proximal and distal tubules were perfused with solutions containing 25 mmol NaHCO3/L. Acidification half-time was increased both in proximal and distal segments and, as a consequence, bicarbonate reabsorption decreased in the presence of UGN (in proximal tubules, from 2.40 ± 0.26 to 1.56 ± 0.21 nmol·cm–2·s–1). When the Na+/H+ exchanger was inhibited by 10−4 mol hexamethylene amiloride (HMA)/L, the control and UGN groups were not significantly different. In the late distal tubule, after HMA, UGN significantly reduced JHCO3–, indicating an effect of UGN on H+-ATPase. These data show that UGN stimulated JK+ by acting on maxi-K channels, and decreased JHCO3– by acting on NHE3 in proximal and H+-ATPase in distal tubules.

Reduced bicarbonate secretion mediates increased distal tubule acidification induced by dietary acid

1996 ◽  
Vol 271 (3) ◽  
pp. F670-F678 ◽  
Author(s):  
D. E. Wesson
Keyword(s):  
Distal Tubule ◽  
Bicarbonate Secretion ◽  
Anesthetized Rats ◽  
Nephron Segment ◽  
Dietary Acid ◽  
Distal Tubules ◽  
Tubule Fluid

We examined the components of net HCO3 reabsorption (H+/HCO3 secretion) in in vivo perfused distal tubules of anesthetized rats to determine the mechanisms by which dietary acid increases acidification in this nephron segment. Animals eating a minimum electrolyte diet drank either 80 mM NH4Cl or 40 mM (NH4)2SO4 for 7-10 days and were compared with controls drinking distilled H2O. Net HCO3 reabsorption in distal tubules perfused with HCO3 concentration ([HCO3]) similar to that in situ (5 mM) was higher in (NH4)2SO4 animals than in control (21.6 +/- 1.8 vs. 12.5 +/- 1.3 pmol.mm-1.min-1, respectively, P < 0.02), but that for NH4Cl (17.9 +/- 1.5 pmol.mm-1.min-1, P = 0.09 vs. control) animals was not. Calculated H+ secretion was not different among groups perfused with the 5 mM HCO3 solution, but calculated HCO3 secretion was lower in (NH4)2SO4 animals than control (-2.4 +/- 0.3 vs. -5.3 +/- 0.6 pmol.mm-1.min-1, respectively, P < 0.02), but that for NH4Cl (-7.2 +/- 0.7 pmol.mm-1.min-1, P = not significant vs. control) was not. When distal tubules were perfused with solutions containing higher [HCO3] (10 nM), both net HCO3 reabsorption and calculated H+ secretion were significantly higher than control in both acid-ingesting groups. The data show that reduced HCO3 secretion mediates the increased distal tubule acidification induced by dietary acid, particularly at the low tubule fluid [HCO3] in situ. The data also show that acid ingested as the Cl- compared with the SO4(-) salt does not reduce HCO3 secretion and less effectively increases acidification in this nephron segment.

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