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)

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.

Unidirectional potassium fluxes in renal distal tubule: effects of chloride and barium

1986 ◽  
Vol 250 (5) ◽  
pp. F885-F894 ◽  
Author(s):  
D. H. Ellison ◽  
H. Velazquez ◽  
F. S. Wright
Keyword(s):  
Secretory Pathway ◽  
Chloride Concentration ◽  
Distal Tubule ◽  
Blocking Agent ◽  
Sprague Dawley ◽  
Potassium Permeability ◽  
Potassium Flux ◽  
Potassium Secretion ◽  
The Difference

Low luminal concentrations of chloride stimulate net potassium secretion by the renal distal tubule, independent of changes in transepithelial voltage. These effects are not prevented by the luminal application of the potassium channel blocking agent barium. Because net potassium secretion comprises secretory and absorptive components, we sought to evaluate the effects of chloride and barium on unidirectional potassium fluxes in the renal distal tubule. In vivo microperfusion methods were used in anesthetized Sprague-Dawley rats. Perfusion solutions contained either 42K or 86Rb as tracers for potassium. Tracer efflux coefficients, indicating apparent potassium permeability, were similar when measured using either isotope. Net potassium flux was determined as the difference between perfusion and collected rate, and unidirectional absorptive potassium flux was calculated as the product of the mean luminal potassium concentration and the tracer efflux coefficient. During perfusion with a solution that resembled fluid normally arriving at the early distal tubule, the absorptive potassium flux was approximately 25% of the unidirectional secretory flux. Reducing lumen chloride concentration increased net potassium secretion, because blood-to-lumen potassium flux increased from 61 +/- 12.7 to 96 +/- 14.6 pmol/min. Barium reduced both absorptive and secretory fluxes but did not prevent the stimulation of net potassium secretion that occurs when luminal chloride concentration is reduced. Apparent potassium permeability during perfusion with a solution that resembled fluid normally arriving at the early distal tubule was 800 nm/s when corrected for voltage. Together with the results of previous experiments, these results are consistent with the presence of a secretory pathway linking potassium with chloride in the luminal membrane of cells of the distal tubule.

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.

Luminal influences on potassium secretion: chloride replacement with sulfate

1982 ◽  
Vol 242 (1) ◽  
pp. F46-F55 ◽  
Author(s):  
H. Velazquez ◽  
F. S. Wright ◽  
D. W. Good
Keyword(s):  
Driving Forces ◽  
Distal Tubule ◽  
Perfusion Fluid ◽  
Cl Transport ◽  
K Secretion ◽  
Cotransport System ◽  
Potassium Secretion ◽  
Transepithelial Voltage ◽  
Series Of Experiments

Electrolyte transport by the renal distal tubule of rats was studied by in vivo continuous microperfusion to determine whether replacing luminal chloride with sulfate would stimulate net potassium secretion. Results in a first series of experiments showed that replacing all Cl in the perfusion fluid with SO4 reduced net Na absorption, reversed the direction of net Cl transport from net absorption to net secretion, increased the lumen-negative transepithelial voltage, and increased net K secretion. In a second series of experiments adding NaCl to a perfusion fluid containing SO4 increased net Na absorption, reversed the direction of net Cl transport from net secretion to net absorption, decreased the transepithelial voltage, and decreased net K secretion. In a third series of experiments addition of 10(-6) M amiloride to a SO4-containing perfusion fluid reduced the transepithelial voltage but did not prevent the increase in K secretion, indicating that the changes in K secretion cannot be explained solely by changes in electrical driving forces. Since net fluid absorption was controlled, the changes in K secretion cannot be attributed to solvent drag effects. In all three series of experiments the rate of net K secretion was increased when luminal Cl concentration was reduced to less than 10 mM. The results suggest the existence of a cotransport system mediating K and Cl absorption by the distal tubule. Inhibition of K absorption by low lumen Cl may contribute to the increased net K secretion seen when nonchloride anions are present in distal fluid.

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.

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.

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.

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.

Luminal influences on potassium secretion: sodium concentration and fluid flow rate

1979 ◽  
Vol 236 (2) ◽  
pp. F192-F205 ◽  
Author(s):  
D. W. Good ◽  
F. S. Wright
Keyword(s):  
Fluid Flow ◽  
Flow Rate ◽  
Distal Tubule ◽  
Sodium Concentration ◽  
Fluid Flow Rate ◽  
Physiological Range ◽  
Luminal Flow ◽  
Potassium Secretion ◽  
K Concentration

Two methods of in vivo continuous microperfusion were used to evaluate separately luminal sodium concentration and fluid flow rate as factors regulating potassium secretion by the renal distal tubule of the rat. Emphasis was placed on evaluating changes in sodium concentration (43-97 mM) and flow rate (4-27 nl/min) within the physiological range. Absolute rates of Na, K, Cl, and H2O transport were measured. Results showed that increasing early distal flow rate without increasing early distal Na concentration significantly increased the absolute rate of potassium secretion by the distal tubule. In contrast, increasing early distal Na concentration, distal Na delivery, and distal Na absorption did not affect potassium secretion if flow rate was not changed. Further studies showed that reducing early distal Na concentration below the physiological range (to 15 mM) caused the direction of net sodium transport to be reversed but did not significantly reduce potassium secretion. Increasing early distal K concentration (to 34 mM) caused the direction of net potassium transport to be reversed. The rate of potassium secretion appears to depend in part on the luminal potassium concentration. Increases in luminal flow rate may increase the rate of potassium secretion by lowering the luminal K concentration.

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)

Sign in / Sign up

Export Citation Format

Share Document