Stimulation of chloride transport by HCO3-CO2 in rabbit cortical collecting tubule

1986 ◽  
Vol 251 (1) ◽  
pp. F49-F56 ◽  
Author(s):  
K. Tago ◽  
V. L. Schuster ◽  
J. B. Stokes
Keyword(s):  
Chloride Transport ◽  
Acid Base ◽  
Cl Transport ◽  
Collecting Tubule ◽  
Acid Base Status ◽  
Stimulation Of ◽  
Rabbit Cortical Collecting Tubule ◽  
Cortical Collecting Tubule

We examined both the role of HCO3-CO2 in Cl transport as well as the effect of in vivo acid-base status on Cl transport by the rabbit cortical collecting tubule. The lumen-to-bath 36Cl tracer flux, expressed as the rate coefficient KCl, was measured in either HEPES-buffered (CO2-free) or HCO3-CO2-containing solutions. Amiloride was added to the perfusate to minimize the transepithelial voltage and thus the electrical driving force for Cl diffusion. Because KCl fell spontaneously with time in HCO3-CO2 solutions in the absence but not the presence of cAMP, we used cAMP throughout to avoid time-dependent changes. Acute in vitro removal of bath HCO3-CO2 reduced KCl. Acetazolamide addition in HEPES-buffered solutions also lowered KCl; KCl could be restored to control values by adding exogenous HCO3-CO2 in the presence of acetazolamide. In vivo acid-base effects on Cl transport were determined by dissecting tubules from either NaHCO3-loaded or NH4Cl-loaded rabbits. Tubules from HCO3-loaded rabbits had higher rates of Cl self exchange. Acute in vitro addition of bath HCO3-CO2 increased KCl and did so to a greater degree in tubules from HCO3-loaded rabbits. Most of this effect of HCO3-CO2 addition on KCl could not be accounted for by Cl-HCO3 exchange; rather, it appeared due to stimulation of Cl self exchange. The data are consistent with 36Cl transport occurring via Cl-HCO3 exchange as well as Cl self exchange. Both processes are acutely stimulated by HCO3 and/or Co2, and both are chronically regulated by in vivo acid-base status.

Direct Na+-K+ pump stimulation by K+ in cortical collecting tubules: a mechanism for early renal K+ adaptation

1989 ◽  
Vol 257 (4) ◽  
pp. F595-F601 ◽  
Author(s):  
Y. Fujii ◽  
A. I. Katz
Keyword(s):  
Turnover Rate ◽  
Rapid Rise ◽  
Hormonal Factors ◽  
Collecting Tubule ◽  
Collecting Tubules ◽  
Stimulation Of ◽  
External K ◽  
Cortical Collecting Tubule

To evaluate the mechanism of increased Na+-K+ pump turnover rate that characterizes the early cortical collecting tubule (CCT) response to K+ loading [Y. Fujii, S. K. Mujais, and A. I. Katz. Am. J. Physiol. 256 (Renal Fluid Electrolyte Physiol. 25): F279-F284, 1989.], we measured ouabain-sensitive 86Rb+ uptake in microdissected rat CCT exposed acutely to elevated ambient K+ in vivo and in vitro. Tubules preincubated in 10 mM K+ had higher 86Rb+ uptake than when preincubated in 5 mM K+ (25.9 +/- 1.2 vs. 18.9 +/- 0.7 pmol.mm-1.min-1, P less than 0.001). KCl infusion (5 mumol.100 g-1.min-1 x 60 min) increased 86Rb+ uptake from 19.2 +/- 1.0 to 31.2 +/- 1.4 pmol.mm-1.min-1, P less than 0.001; the increment was preserved in tubules subsequently treated with monensin or nystatin in vitro, suggesting that pump stimulation was not mediated by increased cell Na+. This conclusion was confirmed in separate experiments in which the effect of K+ on 86Rb+ uptake was not altered by concurrent preincubation with amiloride. Studies with CCT from isolated perfused kidneys and from adrenalectomized animals revealed that stimulation of 86Rb+ uptake by a K+ load occurs rapidly (less than or equal to 5 min) and is independent of hormonal factors. Increased external K+ produces a rapid rise in K+-transporting capacity (turnover rate) of the Na+-K+ pump in CCT. This phenomenon probably represents a direct effect on K+ on the pump and is an important component of the early renal response to increased K+ secretory load.

NH4Cl inhibition of transport in the rabbit cortical collecting tubule

1985 ◽  
Vol 248 (5) ◽  
pp. F631-F637 ◽  
Author(s):  
L. L. Hamm ◽  
C. Gillespie ◽  
S. Klahr
Keyword(s):  
Cation Transport ◽  
Sodium Reabsorption ◽  
Bathing Solution ◽  
Collecting Tubule ◽  
Potassium Secretion ◽  
Transepithelial Voltage ◽  
Rabbit Cortical Collecting Tubule ◽  
Cortical Collecting Tubule

Ammonium has previously been found to inhibit transport in a number of tissues. The present experiments were designed to evaluate the effect of ammonium chloride on transepithelial voltage (VTE) and cation transport in the isolated rabbit cortical collecting tubule perfused in vitro. Peritubular NH4Cl (2-10 mM) inhibited VTE in these tubules independent of bath or lumen pH. Luminal NH4Cl had a similar effect. However, VTE did not change with bath NH4Cl in tubules treated with amiloride or ouabain. Furthermore, when bath PCO2 was lowered simultaneously with the addition of NH4Cl to the bath, little change in VTE occurred, raising the possibility that intracellular pH falls after addition of NH4Cl to the bath. Consistent with the voltage effects, 5 mM NH4Cl in the bathing solution inhibited net sodium reabsorption by 36% and potassium secretion by 44%. Unidirectional lumen-to-bath tracer fluxes were consistent with predominant inhibition of the sodium reabsorptive flux and the potassium secretory flux. These findings may have relevance to metabolic acidosis in vivo because ionic ammonium concentrations attain the levels used in this study.

Cellular actions of cAMP on HCO3(-)-secreting cells of rabbit CCD: dependence on in vivo acid-base status

1994 ◽  
Vol 266 (4) ◽  
pp. F528-F535 ◽  
Author(s):  
C. Emmons ◽  
J. B. Stokes
Keyword(s):  
Anion Exchanger ◽  
Collecting Duct ◽  
Basolateral Membrane ◽  
Disulfonic Acid ◽  
Intercalated Cells ◽  
Cortical Collecting Duct ◽  
Acid Base ◽  
Acid Base Status

HCO3- secretion by cortical collecting duct (CCD) occurs via beta-intercalated cells. In vitro CCD HCO3- secretion is modulated by both the in vivo acid-base status of the animal and by adenosine 3',5'-cyclic monophosphate (cAMP). To investigate the mechanism of cAMP-induced HCO3- secretion, we measured intracellular pH (pHi) of individual beta-intercalated cells of CCDs dissected from alkali-loaded rabbits perfused in vitro. beta-Intercalated cells were identified by demonstrating the presence of an apical anion exchanger (cell alkalinization in response to removal of lumen Cl-). After 180 min of perfusion to permit decrease of endogenous cAMP, acute addition of 0.1 mM 8-bromo-cAMP or 1 microM isoproterenol to the bath caused a transient cellular alkalinization (> 0.20 pH units). In the symmetrical absence of either Na+, HCO3-, or Cl-, cAMP produced no change in pHi. Basolateral dihydrogen 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (0.1 mM) for 15 min before cAMP addition also prevented this alkalinization. In contrast to the response of cells from alkali-loaded rabbits, addition of basolateral cAMP to CCDs dissected from normal rabbits resulted in an acidification of beta-intercalated cells (approximately 0.20 pH units). The present studies demonstrate the importance of the in vivo acid-base status of the animal in the regulation of CCD HCO3- secretion by beta-intercalated cells. The results identify the possible existence of a previously unrecognized Na(+)-dependent Cl-/HCO3- exchanger on the basolateral membrane of beta-intercalated cells in alkali-loaded rabbits.

Effects of calcium on ADH action in the cortical collecting tubule perfused in vitro

1982 ◽  
Vol 243 (5) ◽  
pp. F481-F486
Author(s):  
S. Goldfarb
Keyword(s):  
Hydraulic Conductivity ◽  
Water Flow ◽  
Collecting Tubule ◽  
Bath Water ◽  
Mammalian System ◽  
Rabbit Cortical Collecting Tubule ◽  
Cortical Collecting Tubule

To test the effects of calcium on ADH action in an in vitro mammalian system, the rabbit cortical collecting tubule was studied. After 25 microunits/ml ADH (n=8) in the presence of 1.25 mM calcium bath, water flow (Jv) rose to 1.56 +/- 0.34 nl.mm-1. min-1 and hydraulic conductivity (Lp, cm.s-1.atm-1 X 10(7)) rose to 123 +/- 22. After 25 microunits/ml ADH in the presence of 3.75 mM calcium bath (n=7), Jv rose to 2.96 +/- 0.6 nl.mm-1.min-1 (P less than 0.05 vs. control) and Lp rose to 286 +/- 62 cm.s-1.atm-1 X 10(7) (P less than 0.02 vs. 1.25 mM bath calcium control). Tubules (n=6) perfused with 3.75 mM Ca and bathed in 3.75 mM Ca also showed an Lp of 279 +/- 82 cm.s-1.atm-1 X 10 (7) following 25 microunits/ml ADH. Tubules similarly studied in 1.25 (n=6) or 3.75 mM Ca (n=6) bath but treated with 10(-4) M 8-[p-chlorophenylthio]cAMP demonstrated Lp of 222 +/- 26 and 235 +/- 37 cm.s-1.atm-1 X 10(7), respectively. These data suggest that increased bath Ca enhances ADH- but not cAMP-stimulated water flow in the rabbit cortical collecting tubule. High perfusate Ca2+ does not alter the stimulatory effect of elevated peritubular Ca2+.

scholarly journals Temperature Effects on Haemolymph Acid-Base Status In Vivo and In Vitro in the Two-Striped Grasshopper Melanoplus Bivittatus

1988 ◽  
Vol 140 (1) ◽  
pp. 421-435 ◽  
Author(s):  
JON M. HARRISON
Keyword(s):  
Body Temperature ◽  
Carbonic Acid ◽  
Temperature Shift ◽  
Effect Of Temperature ◽  
Locomotory Activity ◽  
Acid Base ◽  
Protein Dissociation ◽  
Acid Base Status

In this study, I examine the effect of temperature on haemolymph acid-base status in vivo and in vitro in the two-striped grasshopper Melanoplus bivittatus. Melanoplus bivittatus experience wide (up to 40 °C) diurnal body temperature fluctuations in the field, but maintain body temperature relatively constant during sunny days by behavioural thermoregulation. Haemolymph pH was statistically constant (7.12) between 10 and 25°C, but decreased by −0.017 units °C− from 25 to 40°C. Relative alkalinity and fractional protein dissociation were conserved only at body temperatures at which feeding and locomotory activity occur, above 20°C. Haemolymph total CO2 (Ctot) increased from 10 to 20°C and decreased from 20 to 40°C. Haemolymph Pco2 increased from 10 to 20°C and was statistically constant between 20 and 40°C. Carbonic acid pKapp in haemolymph was 6.122 at 35°C, and decreased with temperature by −0.0081 units°C−1. Haemolymph buffer value averaged −35mequivl−1pHunit−1. Haemolymph pH changes with temperature were small (less than −0.004 units°C−1) in vitro at constant Pco2. Therefore, passive physicochemical effects cannot account for the pattern of acid-base regulation in vivo. The temperature shift from 10 to 20°C was accompanied by a net addition of 4.2-6.2 mmoll−1 of bicarbonate equivalents to the haemolymph. The temperature shift from 20 to 40°C was accompanied by a net removal of 10–14 mmoll−1 of bicarbonate equivalents from the haemolymph. Haemolymph acid-base regulation in vivo during temperature changes is dominated by active variation of bicarbonate equivalents rather than by changes in Pco2 as observed for most other air-breathers.

Cell volume regulation of rabbit cortical collecting tubule in anisotonic media

1990 ◽  
Vol 258 (6) ◽  
pp. F1657-F1665 ◽  
Author(s):  
E. Natke
Keyword(s):  
Volume Regulation ◽  
Control Volume ◽  
Cell Volume Regulation ◽  
Volume Regulatory Decrease ◽  
Collecting Tubule ◽  
Collecting Tubules ◽  
Volume Regulatory Increase ◽  
Rabbit Cortical Collecting Tubule ◽  
Cortical Collecting Tubule

Volume regulation of nonperfused rabbit cortical collecting tubules in anisotonic bathing media was examined in vitro. When media osmolality is abruptly increased by 150 mosmol/kgH2O with the addition of NaCl, tubules shrink by 20% but do not volume regulate. However, volume regulatory increase (VRI) is observed when 1 mM butyrate is present in the bathing media or when tubules are pretreated with hypotonic media. When media osmolality is increased, butyrate-treated tubules shrink to 74% of their isotonic control volume. As evidence of volume regulation, butyrate-treated tubules swell while still bathed in hypertonic media, recovering in 30 min 78% of the volume lost due to osmotic shrinkage. The butyrate effect requires external Na+ and is inhibited by amiloride. When media osmolality is lowered to 150 mosmol/kgH2O, nonbutyrate tubules swell before showing typical volume regulatory decrease. When these tubules are returned to isotonic media, they immediately shrink to 78% of control volume before showing evidence of VRI. These results suggest that, under the appropriate conditions, cortical collecting tubules are capable of VRI.

Acidification of luminal fluid by the rabbit cortical collecting tubule perfused in vitro

1982 ◽  
Vol 242 (5) ◽  
pp. F521-F531 ◽  
Author(s):  
B. M. Koeppen ◽  
S. I. Helman
Keyword(s):  
Disulfonic Acid ◽  
Reverse Polarity ◽  
Perfusion Fluid ◽  
Data Support ◽  
Collecting Tubule ◽  
Transepithelial Voltage ◽  
Ph Electrodes ◽  
Rabbit Cortical Collecting Tubule ◽  
Cortical Collecting Tubule

The ability of the rabbit cortical collecting tubule to acidify the luminal fluid was determined with double-barreled antimony pH electrodes. In Na+/K+ Ringer the tubules maintained a transepithelial voltage (VToc) of -45.4 +/- 5.5 mV (bath grounded) and a minimum luminal fluid pH of 5.93 +/- 0.11. Chronic mineralocorticoid pretreatment of the rabbits caused the VToc to become more negative (-78.7 +/- 8.2 mV) and decreased the minimum luminal fluid pH to 5.43 +/- 0.16. In most tubules (control and mineralocorticoid-pretreated) the measured pH was more acidic than could be accounted for by either the lumen-negative VToc or CO2 equilibration of the perfusion fluid. When tubules were perfused and bathed in 0 Na+/0 K+ Ringer they developed a lumen-positive VToc, which was stimulated by mineralocorticoid, was sensitive to the PCO2 of the bathing solutions, but was not dependent on Cl- in either the luminal or bath solutions. Luminal acidification in the absence of Na+ and K+ (pH = 6.05 +/- 0.12) occurred against a lumen-positive VToc of +11.5 +/- 1.9 mV. Addition of 10(-4) M ouabain to the bath of tubules studied in Na+/K+ Ringer caused the VToc to reverse polarity and the luminal fluid pH to increase. In contrast, ouabain had no effect on either the lumen-positive VToc or the minimum luminal fluid pH when added to the bath of tubules in 0 Na+/0 K+ Ringer. Bath addition of 10(-4) M acetazolamide and/or 5 X 10(-4) M 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) caused alkalinization of the luminal fluid in tubules studied in either Na+/K+ or 0 Na+/0 K+ Ringer. In 0 Na+/0 K+ Ringer, acetazolamide and SITS reduced the lumen-positive VToc to near zero. The data support the existence of a distinct acidification mechanism in the rabbit cortical collecting tubule, which is both active and electrogenic.

The Effect of Salt Adaptation and Amiloride on the In Vivo Acid-Base Status of the Euryhaline Toad Bufo Viridis

1981 ◽  
Vol 93 (1) ◽  
pp. 93-99
Author(s):  
U. KATZ
Keyword(s):  
Tap Water ◽  
Salt Adaptation ◽  
Acid Base ◽  
Bufo Viridis ◽  
Acid Base Status ◽  
Simultaneous Decrease ◽  
Toad Bufo

1. The acid-base status of the blood of the toad Bufo viridis was studied during adaptation to high salinity and in tap water containing amiloride. 2. Both salt adaptation and immersion for 2-3 days in 5 x10−4 M amiloride in tap water resulted in a decrease in blood pH (from 7.720 ± 0.026 in tap water to 7.456±0.051 in 500 mOsm NaCl-adapted toads; mean ± S.E.), and a simultaneous decrease in the concentration of HCO3- (from 17.8 ±1.4 in tap water to 9.5±1.2 in salt-adapted toads). 3. In vitro determination of Na+/H+ exchange across the skin showed a 1:1 relation in skins from tap-water-adapted toads; this exchange was inhibited by amiloride. H+ secretion was abolished in skins from salt-adapted toads and the uptake of sodium was reduced.

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