K+ transport in the mesonephric collecting duct system of the toadBufo bufo

2002 ◽  
Vol 205 (7) ◽  
pp. 897-904
Author(s):  
Nadja Møbjerg ◽  
Erik Hviid Larsen ◽  
Ivana Novak

SUMMARYWe studied the mechanisms of K+ transport in cells from isolated and perfused collecting tubules and ducts from the mesonephric kidney of the toad Bufo bufo. Cells were impaled with microelectrodes across the basal cell membrane. The basolateral membrane potential(Vbl) depolarized upon change of bath [K+] from 3 to 20 mmol l-1 demonstrating a large K+ conductance in this membrane. In collecting tubules and collecting ducts a Vbl of -66±2 mV and -74±4 mV depolarized by 30±2 mV and 36±3 mV, respectively (N=23; 15). The K+ channel inhibitor Ba2+ (1 mmol l-1)inhibited the basolateral K+ conductance and depolarized a Vbl of -64±4 mV by 30±6 mV (N=8). Luminal K+ steps (3 to 20 mmol l-1) demonstrated a K+ conductance in the apical cell membrane. In collecting tubules and collecting ducts a Vbl of -70±3 mV and-73±3 mV depolarized by 11±3 mV and 16±3 mV, respectively(N=11; 11). This conductance could also be inhibited by Ba2+, which depolarized a Vbl of -71±5 mV by 9±3 mV (N=5). The pump inhibitor ouabain (1 mmol l-1) depolarized Vbl, but addition of furosemide to bath solution did not affect Vbl. The[K+] in urine varied from 1.3 to 22.8 mmol l-1. In conclusion, we propose that the collecting duct system of B. bufosecretes K+ into the urine via luminal K+channels.

1983 ◽  
Vol 244 (1) ◽  
pp. F35-F47 ◽  
Author(s):  
B. M. Koeppen ◽  
B. A. Biagi ◽  
G. H. Giebisch

Cortical collecting ducts of the rabbit were perfused in vitro and the intracellular potential (Vbl) was measured with KCl-filled microelectrodes. The ratio of apical to basolateral membrane resistance (Ra/Rbl) was estimated from the voltage divider ratio using cable analysis. In control tubules Vbl averaged--84.0 +/- 2.5 mV and Ra/Rbl was 0.83 +/- 0.11. Pretreatment of the rabbits with mineralocorticoid caused Vbl to hyperpolarize to--105.8 +/- 3.1 mV and Ra/Rbl to decrease slightly to 0.62 +/- 0.10. A 10-fold increase of the luminal [K+] caused a 40.6 +/- 3.1 mV depolarization of Vbl in control tubules and a 33.0 +/- 4.2 mV depolarization in tubules from DOCA-pretreated rabbits. Concurrently, Ra/Rbl decreased in both groups, consistent with the existence of a conductive K+ channel at the apical cell membrane. This apical K+ channel was not sensitive to amiloride but was blocked by Ba2+. Conductive movement of Na+ across the apical membrane was also apparent in that Ra/Rbl increased with amiloride from 0.61 +/- 0.10 to 1.45 +/- 0.28. A 10-fold increase in the bath [K+] caused a 28.6 +/- 3.8 and a 49.4 +/- 4.4 mV depolarization of Vbl in tubules obtained from control and DOCA-pretreated rabbits, respectively. In both groups Ra/Rbl increased, suggesting that the basolateral cell membrane also contains a conductive K+ channel. Taken together the results support a model in which the transepithelial reabsorption of Na+ and the transepithelial secretion of K+ are driven by the Na+-K+-ATPase located in the basolateral cell membrane, with passive movement of these ions occurring through separate conductive pathways in the apical cell membrane.


1985 ◽  
Vol 248 (6) ◽  
pp. F858-F868 ◽  
Author(s):  
S. C. Sansom ◽  
R. G. O'Neil

The effects of mineralocorticoid (DOCA) treatment of rabbits on the Na+ and K+ transport properties of the cortical collecting duct apical cell membrane were assessed using microelectrode techniques. Applying standard cable techniques and equivalent circuit analysis to the isolated perfused tubule, the apical cell membrane K+ and Na+ currents and conductances could be estimated from the selective effects of the K+ channel blocker Ba2+ and the Na+ channel blocker amiloride on the apical membrane; amiloride treatment was observed also to decrease the tight junction conductance by an average of 10%. After 1 day of DOCA treatment, the Na+ conductance and current (Na+ influx) of the apical cell membrane doubled and remained elevated with prolonged treatment for up to 2 wk. The apical cell membrane K+ conductance was not influenced after 1 day, although the K+ current (K+ secretion) increased significantly due to an increased driving force for K+ exit. After 4 days or more of DOCA treatment the K+ conductance doubled, resulting in a further modest stimulation in K+ secretion. After 2 wk of DOCA treatment the tight junction conductance decreased by near 30%, resulting in an additional hyperpolarization of the transepithelial voltage, thereby favoring K+ secretion. It is concluded that the acute effect (within 1 day) of mineralocorticoids on Na+ and K+ transport is an increase in the apical membrane Na+ conductance followed by delayed chronic alterations in the apical membrane K+ conductance and tight junction conductance, thereby resulting in a sustained increased capacity of the tubule to reabsorb Na+ and secrete K+.


1987 ◽  
Vol 253 (6) ◽  
pp. F1263-F1272 ◽  
Author(s):  
M. Hunter ◽  
J. D. Horisberger ◽  
B. Stanton ◽  
G. Giebisch

Single collecting tubules of Amphiuma kidneys were perfused in vitro to characterize their electrophysiological properties. The lumen-negative potential (-24 mV) was abolished by amiloride in the lumen and by ouabain in the bath. Ion substitution experiments in the lumen demonstrated the presence of a large sodium conductance in the apical cell membrane, but no evidence was obtained for a significant potassium or chloride conductance. Ion substitutions in the bath solution and the depolarizing effect of barium on the basolateral membrane potential demonstrated the presence of a large potassium conductance in the basolateral cell membrane. Measurements of dilution potentials in amiloride-treated tubules revealed a modest cation selectivity of the paracellular pathway. These results support a cell model in which sodium reabsorption occurs by electrodiffusion across the apical cell membrane and active transport across the basolateral cell membrane. The absence of a detectable potassium conductance in the apical cell membrane suggests that secretion of this ion cannot take place by diffusion from cell to lumen.


1984 ◽  
Vol 247 (2) ◽  
pp. F291-F302 ◽  
Author(s):  
S. C. Sansom ◽  
E. J. Weinman ◽  
R. G. O'Neil

The chloride-conductive properties of the isolated rabbit cortical collecting duct were assessed with microelectrode techniques. The transepithelial, apical, and basolateral membrane potential differences, Vte, Va, and Vb, respectively, were monitored continuously along with periodic measurements of the transepithelial conductance, Gte, and fractional resistance, fRa (ratio of apical to apical plus basolateral membrane resistance). Active transport was eliminated in all experiments by luminal addition of 50 microM amiloride in HCO3-free solutions. Upon reducing the chloride activity in the bath (gluconate replacement), there was a marked depolarization of Vb and decrease in Gte and fRa, demonstrating a major dependence of the basolateral membrane conductance on the bath chloride activity. However, a significant K+ conductance at that barrier was also apparent since raising the bath K+ concentration caused an increase in Gte and fRa and depolarization of Vb. Lowering the chloride activity of the perfusate caused a consistent decrease of Gte but not of fRa, effects consistent with a high C1- conductance of the tight junction and little, if any, apical membrane C1- conductance. By use of the C1- -dependent conductances, the C1- permeabilities at equilibrium were estimated to be near 1.0 X 10(-5) cm X s-1 for the tight junction, PtiC1, and 5 X 10(-5) cm X s-1 for the basolateral cell membrane, PbC1. It is concluded that the paracellular pathway provides a major route for transepithelial C1- transport. Furthermore, since the isotopically measured C1- permeability is severalfold greater than PtiC1, a significant transcellular flux of C1- must exist, implicating a neutral exchange mechanism at the apical cell membrane in series with the high basolateral membrane C1- conductance.


1985 ◽  
Vol 248 (4) ◽  
pp. F500-F506 ◽  
Author(s):  
B. M. Koeppen

Segments of outer medullary collecting duct were dissected from the inner stripe of the rabbit kidney (OMCDi) and perfused in vitro. The conductive properties of the tubule epithelium and individual cell membranes were determined by means of cable analysis and intracellular voltage-recording microelectrodes. In 35 tubules the transepithelial voltage (VT) and resistance (RT) averaged 17.2 +/- 1.4 mV, lumen positive, and 58.6 +/- 5.3 k omega X cm, respectively. The basolateral membrane voltage, (Vbl) was -29.2 +/- 2.1 mV (n = 23). The apical cell membrane did not contain appreciable ion conductances, as evidenced by the high values of apical cell membrane fractional resistance (fRa = Ra/Ra + Rb), which approached unity (0.99 +/- 0.01; n = 23). Moreover, addition of amiloride or BaCl2 to the tubule lumen was without effect on the electrical characteristics of the cell, as was a twofold reduction in luminal [Cl-]. The conductive properties of the basolateral cell membrane were assessed with bath ion substitutions. A twofold reduction in bath [Cl-] depolarized Vbl by 14.7 +/- 0.4 mV (theoretical, 17 mV), while a 10-fold increase in bath [K+] resulted in only a 0.9 +/- 0.4 mV depolarization (theoretical, 61 mV). Substituting bath Na+ with tetramethylammonium (from 150 to 75 mM) was without effect. Reducing bath [HCO-3] from 25 to 5 mM (constant PCO2) resulted in a steady-state depolarization of Vbl of 8.4 +/- 0.4 mV that could not be attributed to conductive HCO-3 movement. Thus, the basolateral cell membrane is predominantly Cl- selective.(ABSTRACT TRUNCATED AT 250 WORDS)


2018 ◽  
Vol 64 (2) ◽  
pp. 60-63 ◽  
Author(s):  
Gergő Ráduly ◽  
Zsuzsánna Pap ◽  
Loránd Dénes ◽  
Annamária Szántó ◽  
Zoltán Pávai

Abstract Introduction: The metanephrogenic zone, renal cortex and renal pyramids develop into their final form by week 13. The metanephric kidney produces large quantities of diluted urine in order to maintain volumes of amniotic fluid. Aquaporins are transmembrane protein channels that enable water transport through biological membranes. Aquaporin 2 (AQP2) is a water channel found in the supranuclear region and apical area of the cell membrane of the kidneys collecting tubule cells. Its main function is reabsorption of water through vasopressin stimulation. Materials and methods: Immunohistochemistry was used to study fetal renal tissue of 34 post-mortem fetuses of 9 weeks to 24 weeks gestational age. Results: AQP2 expression is present in connecting tubules and collecting tubules during the targeted time period. From week 9 to 12, the expression is cytoplasmic. From week 13 to 20 the enhancement of expression in the apical cell membrane occurs with the advancement of fetal age. At the end of the studied period, from week 21 to 24, both cytoplasmic and apical expression were observed. In animal studies AQP2 expression has an increasing trend during development. In contradiction with these results, other authors described low AQP2 levels in the human fetal kidney. Conclusions: This study helps to understand the amniotic fluid’s homeostasis during pregnancy. In the beginning of the fetal period AQP2 protein is present in the cytoplasm of epithelial cells of the collecting duct and distal connecting duct. During the fetal period, AQP2 expression in collecting ducts becomes more enhanced in the apical membrane of the cells.


1990 ◽  
Vol 258 (3) ◽  
pp. F568-F582 ◽  
Author(s):  
G. Frindt ◽  
E. E. Windhager

Experiments were carried out to test whether maneuvers believed to increase intracellular Ca2+ concentration [( Ca2+]cell) inhibit Na transport in cortical collecting tubules (CCTs). Unidirectional Na efflux (JNa1----b) and Na influx (JNab----1) were measured isotopically in isolated perfused renal CCTs of rabbits. The animals were either untreated or pretreated with deoxycorticosterone (DOC) for 1-3 wk. To raise [Ca2+]cell, ionomycin or quinidine were added to, or [Na] reduced in, pertubular fluid. In control DOC-pretreated CCTs JNa1----b tended to saturate as luminal Na concentration was increased, reaching 22.9 +/- 1.2 pmol.cm-1.s-1 at 145 mM. In addition, in these CCTs, in contrast to non-DOC-treated tubules, the apical cell membrane was not found to be rate limiting for Na reabsorption as neither amphotericin B nor vasopressin further enhanced JNa1----b. In non-DOC-treated CCTs 10(-6) M ionomycin inhibited JNa1----b by 44.7%. When DOC-pretreated CCTs were exposed to either 10(-6)M ionomycin or 10(-4)M quinidine, JNa1----b was inhibited by 27 and 26%, respectively, while JNab----1 remained unchanged. This ionomycin-induced inhibition was Ca dependent. Exposure of DOC-pretreated CCTs to 5 mM Na-Ringer solution (Na replaced by choline or N-methyl-D-glucamine) for 30 min reduced JNa1----b by 18-30%. The inhibition of JNa1----b caused by any of the three maneuvers was fully reversed upon addition of amphotericin B to the luminal fluid. The results are consistent with the view that a sustained increase in [Ca2+]cell reduces Na transport by inhibition of the rate of Na+ entry across the apical cell membrane.


1991 ◽  
Vol 261 (1) ◽  
pp. F36-F43 ◽  
Author(s):  
T. Shimizu ◽  
M. Nakamura ◽  
K. Yoshitomi ◽  
M. Imai

To determine the renal tubular site and mechanism of the anticalciuric effects of trichloromethiazide (TCM) and amiloride, we studied the effects of these diuretics on net Ca2+ absorption (JCa) in isolated rabbit connecting tubules (CNT) and cortical collecting ducts (CCD). TCM (100 microM) in the lumen increased JCa in the CNT without affecting lumen-negative transepithelial voltage (VT). This effect was dependent on the amount of parathyroid hormone (PTH, 0.1 or 1 nM) in the bath. TCM had no detectable effect on JCa in the absence of PTH. Addition of 100 microM ouabain to the bath decreased PTH-stimulated JCa and abolished the TCM-stimulated JCa. Elimination of Na+ from the lumen increased PTH-stimulated JCa. Under this condition the ability of TCM to increase JCa was abolished, suggesting that the inhibition of Na+ entry from the lumen with TCM may account for the increase in PTH-stimulated JCa. Elimination of Na+ from the bath in the presence of PTH decreased JCa and abolished the stimulatory effect of TCM on JCa in the presence of PTH. Changes in VT caused by amiloride may not account for the increase in JCa, because JCa was not changed when VT was deflected to more positive direction by increasing bath K+ from 5 to 15 mM. Neither TCM nor amiloride affected JCa in the CCD. From these observations, we speculate that the inhibition of Na+ entry across the apical cell membrane by either thiazides or amiloride may stimulate PTH-induced JCa. The intact Na(+)-Ca2+ antiporter in the basolateral cell membrane is essential for the anticalciuric effect of thiazides and amiloride.


1987 ◽  
Vol 252 (2) ◽  
pp. C121-C127 ◽  
Author(s):  
S. E. Guggino ◽  
W. B. Guggino ◽  
N. Green ◽  
B. Sacktor

The conductive properties of a clone of medullary thick ascending limb (MTAL) cells (GRB-MAL1) were assessed using conventional microelectrodes and the patch clamp technique. The apical cell membrane potential (Va) of MTAL cells was -46 +/- 3 mV. Addition of Ba2+ (1 mM) to the apical solution induced a 22 +/- 2 mV depolarization of Va, whereas furosemide hyperpolarized Va by -5 +/- 1 mV. In the cell-attached patch configuration, the most frequently occurring channel had a single channel conductance of 121 +/- 5 pS and carried outward current. In excised patches, current movement was down the electrochemical K+ gradient. Fluctuations were activated by depolarization of Va and by increasing Ca2+ concentration on the intracellular face. Micromolar amounts of Ba2+ on the intracellular face of the membrane inhibited channel activity. We conclude that cultures of MTAL cells GRB-MAL1 retain at least two of the properties of the mature phenotype, namely, an apical K+ conductance and a sensitivity to loop diuretics; the most frequently occurring channel in the apical cell membrane is a Ca2+-activated, maxi-K+ channel; and, finally Ca2+-activated K+ channels may play a role in generating the apical K+ conductance in cultured MTAL cells.


Sign in / Sign up

Export Citation Format

Share Document