Acid extrusion in S3 segment of rabbit proximal tubule. II. Effect of basolateral CO2/HCO3-

1995 ◽  
Vol 268 (2) ◽  
pp. F193-F203 ◽  
Author(s):  
L. K. Chen ◽  
W. F. Boron

Monitoring intracellular absorbance spectra of the pH-sensitive dye dimethylcarboxyfluorescein we studied intracellular pH (pHi) regulation in the isolated perfused S3 segment of the rabbit proximal tubule. In the preceding study [Am. J. Physiol. 268 (Renal Fluid Electrolyte Physiol. 37): F179-F192, 1995.], we demonstrated that simultaneously adding CO2/HCO3- to both lumen and bath stimulated two acid-extruding mechanisms, one dependent on luminal Na+ (a Na+/H+ exchanger) and one independent of Na+ (presumably a H+ pump). Here, we examine the effects of adding CO2/HCO3- to the lumen only or to the bath only. Over a broad pHi range, the total rate of pHi recovery from an acid load in the presence of Na+ was not increased by luminal CO2/HCO3-. On the other hand, basolateral CO2/HCO3- increased the pHi recovery rate to an even greater extent than had bilateral CO2/HCO3-. Regarding the Na(+)-independent pHi recovery mechanism, we found that luminal CO2/HCO3- failed to increase the pHi recovery rate compared with controls also studied in the absence of Na+. Neither did luminal CO2/HCO3- significantly affect the lag time between the maximal acid load and the initiation of the Na(+)-independent pHi recovery (approximately 147 vs. approximately 212 s in controls). On the other hand, adding CO2/HCO3- to only the bath substantially increased the rate of Na(+)-independent pHi recovery, which generally was greater than that observed with bilateral CO2/HCO3-. CO2/HCO3- only in the bath also reduced the lag time to approximately 51 s, which is not significantly different from the value of approximately 36 s observed with bilateral CO2/HCO3-. Our data are consistent with the hypothesis that basolateral (but not luminal) CO2/HCO3- stimulates both a luminal Na+/H+ exchanger and a luminal H+ pump.

1995 ◽  
Vol 268 (2) ◽  
pp. F179-F192 ◽  
Author(s):  
L. K. Chen ◽  
W. F. Boron

Monitoring the absorbance spectra of the pH-sensitive dye dimethylcarboxyfluorescein, we studied intracellular pH (pHi) regulation in the isolated perfused S3 segment of rabbit proximal tubule. To explain a previous observation, that steady-state pHi is higher in the presence than in the absence of CO2/HCO3- (N. L. Nakhoul, L. K. Chen, and W. F. Boron. J. Gen. Physiol. 102: 1171-1205, 1993), we examined the effect of bilateral (i.e., luminal and basolateral) CO2/HCO3- on the acid extrusion processes responsible for recovery of pHi from acid loads. To compute fluxes from rates of pHi change, we determined the pHi dependence of intrinsic intracellular buffering power, which was approximately 50 mM/pH at pHi 6.5 and fell linearly to approximately 20 mM at pHi 7.4. In one series of experiments, we monitored the rate of pHi recovery from an acid load imposed by an NH4+/NH3 prepulse. Over a broad range of pHi values, total net acid extrusion was approximately four times higher in bilateral presence of CO2/HCO3- than in its absence. In a second group of experiments, which were designed to determine the effect of CO2/HCO3- on luminal Na+/H+ exchange, we monitored the rate of pHi recovery elicited by adding Na+ back to only the lumen, after first removing Na+ bilaterally. Initial rate of luminal Na(+)-dependent net acid extrusion in presence of CO2/HCO3- was approximately 229 microM/s (pHi 6.92), approximately 1.8 times higher than the flux of approximately 127 microM/s (P < 0.005) obtained in absence of CO2/HCO3- (pHi 6.66). CO2/HCO3- alkali-shifted the flux vs. pHi relationship by 0.3-0.4 pH units. In a final series of experiments, we examined the effect of CO2/HCO3- on the Na(+)-independent alkalinization that follows the rapid, initial acidification elicited by bilateral Na+ removal. In the presence of CO2/HCO3-, lag time for initiation of the Na(+)-independent alkalinization was only approximately 36 vs. approximately 211 s (P < 0.002) in absence of CO2/HCO3-. Also, Na(+)-independent net acid extrusion rate was approximately two to three times higher in presence than in absence of CO2/HCO3- at comparable pHi. This Na(+)-independent acid extrusion was insensitive to N-ethylmaleimide (2 mM), but was inhibited approximately 94% by efforts to deplete intracellular ATP (i.e., removal of glucose and amino acids, plus addition of 2 mM cyanide and 10 mM iodoacetic acid). Stimulation of luminal Na+/H+ exchange and Na(+)-independent acid extrusion appears to be the major, if not the entire, explanation for the higher steady-state pHi caused by bilateral addition of CO2/HCO3-.


1988 ◽  
Vol 92 (3) ◽  
pp. 369-393 ◽  
Author(s):  
N L Nakhoul ◽  
A G Lopes ◽  
J R Chaillet ◽  
W F Boron

We used the absorbance spectrum of 4',5'-dimethyl-5-(and 6) carboxyfluorescein to measure intracellular pH (pHi) in the isolated, perfused S3 segment of the rabbit proximal tubule. Experiments were conducted in HCO3- -free solutions. pHi recovered from an acid load imposed by an NH4+ prepulse, indicating the presence of one or more active acid-extrusion mechanisms. Removal of Na+ from bath and lumen caused pHi to decrease by approximately 0.6, whereas Na+ readdition caused complete pHi recovery. Removal of Na+ from the bath caused only a slow pHi decrease that was enhanced about fourfold when Na+ was subsequently removed from the lumen also. Similarly, the pHi recovery produced by the readdition of Na+ to the bath and lumen was about ninefold faster than when Na+ was returned to the bath only. Amiloride (1-2 mM) inhibited the pHi recovery that was elicited by returning 15 or 29 mM Na+ to lumen by only approximately 30%. However, in the absence of external acetate (Ac-), 1 mM amiloride inhibited approximately 66% of the pHi recovery induced by the readdition of 29 mM Na+ to the lumen only. The removal of external Ac- reduced the pHi recovery rate from an NH4+-induced acid load by approximately 47%, and that elicited by Na+ readdition, by approximately 67%. Finally, when bilateral removal of Na+ was maintained for several minutes, pHi recovered from the initial acidification, slowly at first, and then more rapidly, eventually reaching a pHi approximately 0.1 higher than the initial one. This Na+-independent pHi recovery was not significantly affected by lowering [HEPES]o from 32 to 3 mM or by adding N'N'-dicyclohexylcarbodiimide (10(-4) M) to the lumen, but it was reduced approximately 57% by iodoacetate (0.5 mM) plus cyanide (1 mM). We conclude that in the nominal absence of HCO3-, three transport systems contribute to acid extrusion by S3 cells: (a) a Na+-independent mechanism, possibly an H+ pump; (b) a Na-H exchanger, confined primarily to the luminal membrane; and (c) an Ac- and luminal Na+-dependent mechanism. The contribution of these three mechanisms to total acid extrusion, assessed by the rapid readdition of Na+, was approximately 13, approximately 30, and approximately 57%, respectively.


1990 ◽  
Vol 258 (2) ◽  
pp. F371-F381 ◽  
Author(s):  
N. L. Nakhoul ◽  
L. K. Chen ◽  
W. F. Boron

We studied the role of basolateral HCO3- transport in the regulation of intracellular pH (pHi) in the isolated perfused S3 segment of the rabbit proximal tubule. pHi was calculated from absorbance spectra of the pH-sensitive dye dimethylcarboxyfluorescein. Solutions were normally buffered to pH 7.4 at 37 degrees C with 25 mM HCO3- 5% CO2. pHi fell by approximately 0.17 when luminal [HCO3-] was lowered to 5 mM at fixed PCO2 (i.e., reducing pH to 6.8) but by approximately 0.42 when [HCO3-] in the bath (i.e., basolateral solution) was lowered to 5 mM. The pHi decrease elicited by reducing bath [HCO3-] was substantially reduced by removal of Cl- or Na+, suggesting that components of basolateral HCO3- transport are Cl- and/or Na+ dependent. We tested for the presence of basolateral Cl-HCO3 exchange by removing bath Cl-. This caused pHi to increase by approximately 0.23, with an initial rate of approximately 100 X 10(-4) pH/s. Although the initial rate of this pHi increase was not reduced by removing Na+ bilaterally, it was substantially lowered by the nominal removal of HCO3- from bath and lumen or by the addition of 0.1 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) to the bath. The results thus suggest that a Na-independent Cl-HCO3 exchanger is present at the basolateral membrane. We tested for the presence of basolateral Na-HCO3 cotransport by removing bath Na+. This caused pHi to fall reversibly by approximately 0.26 with initial rates of pHi decline and recovery being approximately 30 and approximately 41 X 10(-4) pH/s, respectively. Although the bilateral removal of Cl- had no effect on these rates, the nominal removal of HCO3- or the presence of DIDS substantially slowed the pHi changes. Thus, in addition to a Cl-HCO3 exchanger, the basolateral membrane of the S3 proximal tubule also appears to possess a Na-HCO3 cotransport mechanism. The data do not rule out the possibility of other basolateral HCO3- transporters.


2002 ◽  
Vol 283 (4) ◽  
pp. F771-F783 ◽  
Author(s):  
Yukio Miyata ◽  
Yasushi Asano ◽  
Shigeaki Muto

Using the pH-sensitive fluorescent dye BCECF, we compared the effects of hyperosmotic urea on basolateral Na+/H+ exchange (NHE) with those of hyperosmotic mannitol in isolated nonperfused proximal tubule S2 segments from mice lacking both the mdr1a and mdr1b genes (KO) and wild-type (WT) mice. All the experiments were performed in CO2/HCO[Formula: see text]-free HEPES solutions. Osmolality of the peritubular solution was raised from 300 to 500 mosmol/kgH2O by adding mannitol or urea. NHE activity was assessed by the Na+-dependent acid extrusion rate ( J H) after an acid load with NH4Cl prepulse. In WT mice, hyperosmotic mannitol had no effect on J H at over the entire range of intracellular pH (pHi) studied (6.20–6.90), whereas in KO mice it increased J H at a pHi range of 6.20–6.45. In contrast, in both WT and KO mice, hyperosmotic urea increased J H at a pHi range of 6.20–6.90. In KO mice, J H in a hyperosmotic urea solution were similar to those in a hyperosmotic mannitol solution at a pHi range of 6.20–6.40 but were greater than in a hyperosmotic mannitol solution at a pHi range of 6.45–6.90. In WT mice, hyperosmotic urea caused an increase in V max without changing K mfor peritubular Na+. Staurosporine (the PKC inhibitor) inhibited hyperosmotic mannitol-induced NHE activation in KO mice, whereas it had no effect on hyperosmotic urea-induced NHE activation in WT or KO mice. Genistein (the tyrosine kinase inhibitor) inhibited hyperosmotic urea-induced NHE activation in WT and KO mice, whereas it caused no effect on hyperosmotic mannitol-induced NHE activation in KO mice. We conclude that hyperosmotic urea activates basolateral NHE via tyrosine kinase in tubules from both WT and KO mice, whereas hyperosmotic mannitol activates it via PKC only in tubules from KO mice.


2008 ◽  
Vol 53 (No. 4) ◽  
pp. 145-151
Author(s):  
J.P. Ramon-Ugalde ◽  
J. Folch ◽  
M.J. Cocero ◽  
R.E. Piña-Aguilar ◽  
J.L. Alabart

The efficiency of embryo recovery in a superovulatory treatment was studied by perfusing the oviduct or the uterine horn in 3.5 and 7 days after sponge withdrawal, respectively. Eighty-four and seventy ewes of Aragonesa breed were used as embryo donors and receptors, respectively. The donors were distributed in 3 replications. The oestrus was synchronized with the insertion of FGA intravaginal sponges (30 mg) for 13 days. Six intramuscular injections of 18 mg pFSH were applied in decreasing doses at 12 hour intervals starting 48 hours after sponge withdrawal. The recovery rate (RR) (83.2 vs. 75.8%), the viability rate (VR) (73.5 vs. 47.2%) and the number of viable embryos (VE) per donor ewe (5.9 ± 0.79 vs. 3.0 ± 0.37) were higher (<I>P</I> < 0.01) in ewes whose perfusion was done directly in oviducts. The interval from sponge withdrawal to oestrus had no influence on RR in any groups; however it had an effect on the VR in 3.5 and 7 days old embryos. Embryos from ewes showing the oestrus within 20 hours after sponge withdrawal had a higher viability. On the other hand, using morphologic criteria, 26.5% and 52.7% of 3.5 and 7 days old embryos, respectively, were discarded before transfer. The percentage of ewes in each group that became pregnant was similar in both groups. We conclude that in superovulated ewes the embryo recovery rate, viability and number of viable embryos are higher in embryos recovered from the oviduct compared to those recovered from the uterus, without decreasing the conception rate and the viability rate is higher in ewes that show the oestrus 20 hours before sponge withdrawal.


1975 ◽  
Vol 229 (6) ◽  
pp. 1654-1661 ◽  
Author(s):  
RA Kramp ◽  
RH Lenoir

Permeability of the tubular epithelium to urate presented on the peritubular side was studied in anesthetized rats during mannitol diuresis by capillary microinjections of [14C]urate and [3H]inulin, [14C]PAH and [3H]inulin, or [14C]urate and [3H]PAH. Recovery of isotopes was determined in urine collected serially from the injected and contralateral kidney. Appearance and peak excretion of urate in the experimental but not in the contralateral kidney preceded inulin and coincided with PAH, indicating proximal permeability to urate. Recovery of urate was higher from the injected than from the contralateral kidney. Urate precession and recovery did not change after addition of PAH (1.5-6.4 mm) to [14C]urate-[3H]inulin solutions, whereas they decreased significantly in the experimental kidney after pyrazinoate (1.6-3.2 mM) addition. On the other hand, no effect of urate on [14C]PAH-[3H]inulin injections was detectable. These findings are suggestive of a carrier-mediated transtubular influx of urate in rat proximal tubule. Absence of competition with PAH may suggest differences in the secretory mechanisms for organic acids.


1993 ◽  
Vol 102 (6) ◽  
pp. 1171-1205 ◽  
Author(s):  
N L Nakhoul ◽  
L K Chen ◽  
W F Boron

We used the absorbance spectrum of the pH-sensitive dye dimethylcarboxyfluorescein to monitor intracellular pH (pHi) in the isolated perfused S3 segment of the rabbit proximal tubule, and examined the effect on pHi of switching from a HEPES to a CO2/HCO3- buffer in the lumen and/or the bath (i.e., basolateral solution). Solutions were titrated to pH 7.40 at 37 degrees C. With 10 mM acetate present bilaterally (lumen and bath), this causing steady-state pHi to be rather high (approximately 7.45), bilaterally switching the buffer from 32 mM HEPES to 5% CO2/25 mM HCO3- caused a sustained fall in pHi of approximately 0.26. However, with acetate absent bilaterally, this causing steady-state pHi to be substantially lower (approximately 6.9), bilaterally switching to CO2/HCO3- caused a transient pHi fall (due to the influx of CO2), followed by a sustained rise to a level approximately 0.18 higher than the initial one. The remainder of the experiments was devoted to examining this alkalinization in the absence of acetate. Switching to CO2/HCO3- only in the lumen caused a sustained pHi fall of approximately 0.15, whereas switching to CO2/HCO3- only in the bath caused a transient fall followed by a sustained pHi increase to approximately 0.26 above the initial value. This basolateral CO2/HCO3(-)-induced alkalinization was not inhibited by 50 microM DIDS applied shortly after CO2/HCO3- washout, but was slowed approximately 73% by DIDS applied more than 30 min after CO2/HCO3- washout. The rate was unaffected by 100 microM bilateral acetazolamide, although this drug greatly reduced CO2-induced pHi transients. The alkalinization was not blocked by bilateral removal of Na+ per se, but was abolished at pHi values below approximately 6.5. The alkalinization was also unaffected by short-term bilateral removal of Cl- or SO4=. Basolateral CO2/HCO3- elicited the usual pHi increase even when all solutes were replaced, short or long-term (&gt; 45 min), by N-methyl-D-glucammonium/glucuronate (NMDG+/Glr-). Luminal CO2/HCO3- did not elicit a pHi increase in NMDG+/Glr-. Although the sustained pHi increase elicited by basolateral CO2/HCO3- could be due to a basolateral HCO3- uptake mechanism, net reabsorption of HCO3- by the S3 segment, as well as our ACZ data, suggest instead that basolateral CO2/HCO3- elicits the sustained pHi increase either by inhibiting an acid-loading process or stimulating acid extrusion across the luminal membrane (e.g., via an H+ pump).


2002 ◽  
Vol 282 (4) ◽  
pp. F718-F729 ◽  
Author(s):  
Yukio Miyata ◽  
Yasushi Asano ◽  
Shigeaki Muto

Using the pH-sensitive fluorescent dye 2′,7′-bis(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester, we examined the effects of hyperosmotic mannitol on basolateral Na+/H+ exchange (NHE) activity in isolated nonperfused proximal tubule S2 segments from mice lacking both the mdr1a and mdr1b genes (KO) and wild-type mice (WT). All experiments were performed in CO2/HCO[Formula: see text]-free HEPES solutions. Osmolality of the peritubular solution was raised from 300 to 500 mosmol/kgH2O by the addition of mannitol. NHE activity was assessed by Na+-dependent acid extrusion rates ( J H) after an acid load with NH4Cl prepulse. Under isosmotic conditions, J H values at a wide intracellular pH (pHi) range of 6.20–6.90 were not different between the two groups. In WT mice, hyperosmotic mannitol had no effect on J H at the wide pHi range. In contrast, in KO mice, hyperosmotic mannitol increased J H at a pHi range of 6.20–6.45 and shifted the J H-pHi relationship by 0.15 pH units in the alkaline direction. In KO mice, hyperosmotic mannitol caused an increase in maximal velocity without changing the Michaelis-Menten constant for peritubular Na+. Exposure of cells from WT mice to the hyperosmotic mannitol solution including the P-gp inhibitor cyclosporin A increased J H (at pHi6.30) to an extent similar to that in cells from KO mice exposed to hyperosmotic mannitol alone. In KO mice, staurosporine and calphostin C inhibited the hyperosmotic mannitol-induced increase in J H. The stimulatory effect of hyperosmotic mannitol on J H was mimicked by addition to the isosmotic control solution, including phorbol 12-myristate 13-acetate (PMA; the PKC activator). In WT mice, hyperosmotic mannitol with PMA increased J H. We conclude that, in the absence of P-gp activity, hyperosmotic mannitol activates basolateral NHE via protein kinase C, whereas in the presence of P-gp activity, it does not.


1979 ◽  
Vol 42 (05) ◽  
pp. 1388-1397
Author(s):  
Shigeru Hayashi ◽  
Kaneo Yamada

SummaryUsing treatment with thrombin associated with trans-aminomethylcyclohexane carboxylic acid (t-AMCHA), a simple and rapid method for isolating soluble fibrin complexes (SFC) from fibrinogen in the plasma was developed. By this procedure, the recovery rates of SFC and early FDP (mainly X) increased according to the concentration of t-AMCHA, reaching a maximum at 286 mM t-AMCHA. On the other hand, the recovery rate of fibrinogen remained below 1.5% and that of late FDP was almost 100% at all concentrations of t- AMCHA. These results suggested that SFC and FDP could be isolated from fibrinogen by thrombin and t-AMCHA (286 mM) treatment. Moreover, it was possible to isolate SFC from FDP using gel filtration after treatment with thrombin and t-AMCHA. The SFC could be quantified by assay of the eluted fractions containing SFC by the staphylococcal clumping test.


1987 ◽  
Vol 253 (2) ◽  
pp. F282-F289
Author(s):  
J. L. Atkins ◽  
M. B. Burg

Steady-state pH (defined as the limiting pH reached at slow flow rates) was measured in isolated perfused rabbit proximal straight tubules (S2). With normal bath conditions (pH 7.4, bicarbonate 25 mM) the luminal steady-state pH was 6.85. Steady-state pH was directly related to bath pH and bicarbonate, but not to bath PCO2. Lowering of bath pH or bicarbonate consistently decreased luminal steady-state pH, and raising either caused steady-state pH to increase. When bath PCO2 was increased, on the other hand, steady-state pH either increased or decreased, depending on the concomitant changes in bicarbonate and pH. The changes in steady-state pH observed in the present studies following alterations in bath pH and bicarbonate concentration should, when extrapolated to the in vivo kidney, result in decreased delivery of bicarbonate from the proximal tubule in acidosis and increased delivery in alkalosis. The effects of potassium and chloride were also determined. Removal of potassium from the bath increased the steady-state pH, but removal of chloride from both the perfusate and bath had no significant effect.


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