pH regulation and response to AVP in A10 cells differ markedly in the presence vs. absence of CO2-HCO3-

1990 ◽  
Vol 259 (3) ◽  
pp. C471-C483 ◽  
Author(s):  
D. Kikeri ◽  
M. L. Zeidel ◽  
B. J. Ballermann ◽  
B. M. Brenner ◽  
S. C. Hebert
Keyword(s):  
Steady State ◽  
Ph Regulation ◽  
Disulfonic Acid ◽  
Potential Contribution ◽  
Vasoactive Agents ◽  
Cell Responses ◽  
Extrusion Mechanism ◽  
Acid Extrusion ◽  
Ambient Co2 ◽  
Stimulation Of

The fluorescent pH-sensitive dye 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) was used to determine the effect of ambient CO2-HCO3- on the regulation of intracellular pH (pHi) and the pHi response to arginine vasopressin (AVP) in A10 vascular smooth muscle (VSM) cells. Steady-state pHi averaged 7.04 +/- 0.02 in the absence and 7.25 +/- 0.01 in the presence of CO2-HCO3-. In the absence of CO2-HCO3-, virtually all (greater than 96%) of the acid extrusion from acidification occurred by amiloride-sensitive Na(+)-H+ exchange. However, in the presence of CO2-HCO3-, acid extrusion after acidification occurred by both Na(+)-H+ exchange and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-sensitive Na(+)-dependent Cl(-)-HCO3- exchange. In CO2-HCO3(-)-containing media, amiloride-sensitive Na(+)-H+ exchange mediated 85% of acid extrusion at a pHi of 6.48, but the DIDS-sensitive acid extrusion mechanism (NA(+)-dependent Cl(-)-HCO3- exchange) was the dominant acid extrusion mechanism at a pHi of 6.94. Base exited A10 cells by a DIDS-sensitive process consistent with Na(+)-independent Cl(-)-HCO3- exchange. Both amiloride- and DIDS-sensitive processes regulated steady-state pHi in CO2-HCO3-. AVP (10(-7) M) alkalinized steady-state pHi in the absence of CO2-HCO3- (delta pHi = 0.08 +/- 0.01 pH units) by stimulating Na(+)-H+ exchange; however, AVP did not alter pHi of untreated cells in CO2-HCO3- (delta pHi = -0.01 +/- 0.01 pH units) because of concomitant stimulation of Na(+)-independent Cl(-)-HCO3-exchange. We conclude that the steady-state pHi, the mechanisms of pHi regulation, and the pHi response to AVP in A10 cells are critically influenced by the presence of extracellular CO2-HCO3-. Thus the potential contribution of pHi changes to VSM cell responses to vasoactive agents should be evaluated in the presence of CO2-HCO3-.

pH regulation in single glomerular mesangial cells. I. Acid extrusion in absence and presence of HCO3-

1988 ◽  
Vol 255 (6) ◽  
pp. C844-C856 ◽  
Author(s):  
G. Boyarsky ◽  
M. B. Ganz ◽  
R. B. Sterzel ◽  
W. F. Boron
Keyword(s):  
Steady State ◽  
Loading Rate ◽  
Mesangial Cells ◽  
Ph Regulation ◽  
Disulfonic Acid ◽  
Glomerular Mesangial Cells ◽  
Fluorescence Excitation ◽  
Dependent Transport ◽  
Acid Extrusion ◽  
Acid Loading

We have developed a technique to measure the fluorescence of a pH-sensitive dye (2,7-biscarboxyethyl-5(6)-carboxyfluorescein) in single glomerular mesangial cells in culture. The intracellular fluorescence excitation ratio of the dye was calibrated using the nigericin-high-K+ approach. In the absence of CO2-HCO3-, mesangial cells that are acid loaded by an NH+4 prepulse exhibit a spontaneous intracellular pH (pHi) recovery that is blocked either by ethylisopropylamiloride (EIPA) or removal of external Na+. This pHi recovery most probably reflects the activity of a Na+-H+ exchanger. When the cells are switched from a N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered solution to one containing CO2-HCO3-, there is an abrupt acidification due to CO2 entry, which is followed by a spontaneous recovery of pHi to a steady-state value higher than that prevailing in HEPES. Both the rate of recovery and the higher steady-state pHi imply that the application of CO2-HCO3- introduces an increase in net acid extrusion from the cell. One third of total net acid extrusion in CO2-HCO3- is EIPA sensitive and most likely is mediated by the Na+-H+ exchanger. The remaining two thirds of acid extrusion could be caused by a decrease in the background acid-loading rate and/or the introduction of a new, HCO3- -dependent acid-extrusion mechanism. The HCO3- -induced alkalinization cannot be accounted for by a HCO3- -induced reduction in the acid-loading rate. The latter can be estimated by applying EIPA in the absence of HCO3- and observing the rate of pHi decline. We found that this acid-loading rate is only about one fifth as great as the total net acid extrusion rate in the presence of HCO3-. Indeed, two thirds of net acid extrusion in HCO3- is blocked by 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), an inhibitor of HCO3- -dependent transport. Furthermore, the effects of EIPA and SITS were additive. Thus, in the presence of CO2-HCO3-, a SITS-sensitive-HCO3- -dependent transporter is the dominant mechanism of acid extrusion. This mechanism also accounts for the increase in steady-state pHi on addition of CO2-HCO3-.

Control of intracellular pH during regulatory volume decrease in HL-60 cells

1994 ◽  
Vol 267 (4) ◽  
pp. C1057-C1066 ◽  
Author(s):  
K. R. Hallows ◽  
D. Restrepo ◽  
P. A. Knauf
Keyword(s):  
Intracellular Ph ◽  
Ph Regulation ◽  
Regulatory Volume Decrease ◽  
Transport Systems ◽  
Disulfonic Acid ◽  
Volume Dependence ◽  
Supportive Role ◽  
22Na Uptake ◽  
Volume Decrease ◽  
Stimulation Of

Intracellular pH (pHi) homeostasis was investigated in human promyelocytic leukemic HL-60 cells as they undergo regulatory volume decrease (RVD) in hypotonic media to determine how well pHi is regulated and which transport systems are involved. Cells suspended in hypotonic (50-60% of isotonic) media undergo a small (< 0.2 pH units), but significant (P < 0.05), intracellular acidification within 5 min. However, after 30 min of RVD, pHi is not significantly different from the initial pHi in 20 mM HCO3- medium and is significantly higher in HCO3(-)-free medium. Experiments performed in media with or without 150 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and HCO3- demonstrate that the anion exchanger (AE) mediates a net Cl- influx, with compensating HCO3- efflux, during RVD. To determine which transport systems are involved in counteracting this tendency toward acidification, we measured transport rates and examined the effect of transport system inhibitors on pHi. We found that inhibition of Na+/H+ exchange (NHE) with 12.5 microM ethylisoproplamiloride (EIPA) causes pHi to fall significantly by the end of 30 min of RVD. As assessed by EIPA-sensitive 22Na+ uptake measurements, NHE, largely dormant under resting isotonic conditions, becomes significantly activated by the end of 30 min of RVD, despite recovery of pHi and cell volume to near-normal levels. Thus a shift in the normal pHi dependence and/or volume dependence of NHE activity must occur during RVD under hypotonic conditions. In contrast, H(+)-monocarboxylate cotransport appears to play only a supportive role in pH regulation during RVD, as indicated by lack of stimulation of [14C]lactate efflux during RVD.

pH regulation in barnacle muscle fibers: dependence on intracellular and extracellular pH

1979 ◽  
Vol 237 (3) ◽  
pp. C185-C193 ◽  
Author(s):  
W. F. Boron ◽  
W. C. McCormick ◽  
A. Roos
Keyword(s):  
Ph Regulation ◽  
Muscle Fibers ◽  
Extracellular Ph ◽  
Disulfonic Acid ◽  
Extrusion Rate ◽  
Barnacle Muscle ◽  
Buffering Power ◽  
Acid Extrusion ◽  
Barnacle Muscle Fibers ◽  
Very High

Intracellular pH (pHi) regulation was studied in acid-loaded barnacle muscle fibers by monitoring recovery of pHi with a pH-sensitive microelectrode. By multiplying the rate of pHi recovery by total intracellular buffering power, the acid extrusion rate was obtained. The acid extrusion rate was greatest at low values of pHi, and declined toward zero as pHi approached normal levels. It increased as the extracellular pH (pHo) was raised either by increasing external [HCO3] ([HCO3]o) at constant PCO2 or by decreasing PCO2 at constant [HCO3]o, but more so in the former case than in the latter. These observations suggest that pHo per se is an important determinant of the acid extrusion rate, but that raising [HCO3]o by itself also stimulates acid extrusion. This would be expected if acid extrusion involves the inward movement of HCO3. When fibers were exposed to HCO3-containing solutions at very low or very high pHo, pHi drifted downward or upward, respectively; thbe drifts were inhibited by 4-acetamido-4' isothiocyanostilbene-2,2' disulfonic acid (SITS). Our results are discussed in terms of possible mechanisms of acid extrusion.

scholarly journals Effect of basolateral CO2/HCO3- on intracellular pH regulation in the rabbit S3 proximal tubule.

1993 ◽  
Vol 102 (6) ◽  
pp. 1171-1205 ◽  
Author(s):  
N L Nakhoul ◽  
L K Chen ◽  
W F Boron
Keyword(s):  
Steady State ◽  
Proximal Tubule ◽  
Intracellular Ph ◽  
Ph Regulation ◽  
Uptake Mechanism ◽  
Luminal Membrane ◽  
S3 Segment ◽  
Acid Extrusion ◽  
Acid Loading

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).

Acid extrusion in S3 segment of rabbit proximal tubule. I. Effect of bilateral CO2/HCO3-

1995 ◽  
Vol 268 (2) ◽  
pp. F179-F192 ◽  
Author(s):  
L. K. Chen ◽  
W. F. Boron
Keyword(s):  
Steady State ◽  
Proximal Tubule ◽  
Initial Rate ◽  
Iodoacetic Acid ◽  
Buffering Power ◽  
Acid Load ◽  
S3 Segment ◽  
Series Of Experiments ◽  
Acid Extrusion ◽  
Stimulation Of

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-.

pH regulation in the vertebrate central nervous system: microelectrode studies in the brain stem of the lamprey

1987 ◽  
Vol 65 (5) ◽  
pp. 986-993 ◽  
Author(s):  
Mitchell Chesler
Keyword(s):  
Brain Stem ◽  
Ph Regulation ◽  
Disulfonic Acid ◽  
Small Rise ◽  
Free Media ◽  
Acid Extrusion ◽  
Acid Loading ◽  
The Brain ◽  
Vertebrate Central Nervous System ◽  
Dependent Mechanism

Studies of intracellular pH (pHi) in nervous tissue are summarized and recent investigation of intracellular and extracellular pH (pHo) in the isolated brain stem of the lamprey is reviewed. In the lamprey, pHi regulation was studied in single reticulospinal neurons using double-barrel ion-selective microelectrodes (ISMs). In nominally [Formula: see text]-free HEPES-buffered media, acute acid loading was followed by a spontaneous recovery of pHi requiring 10–20 min and was associated with a prolonged rise in intracellular Na+. The recovery of pHi was blocked by 1–2 mM amiloride. Amiloride also caused a small rise in pHo. Substitution of external Na+ caused a slow intracellular acidification and extracellular alkalinization. Return of external Na+ reversed these effects. Transition from HEPES to [Formula: see text]-buffered media increased the rate of acid extrusion during recovery of pHi. Recovery in [Formula: see text]-buffered media was inhibited by 4,4′-diisothio-cyanostilbene-2,2′-disulfonic acid and was slowed after exposure to Cl−-free media. Following inhibition of acid extrusion by amiloride, transition to [Formula: see text] media restored pHi recovery. These data indicate that lamprey neurons recover from acute acid loads by both Na+–H+ exchange and an independent [Formula: see text]-dependent mechanism. Evidence for [Formula: see text]-dependent acid extrusion in other vertebrate cells and the protocols of pHi studies using ISMs are discussed.

pH regulation in single glomerular mesangial cells. II. Na+-dependent and -independent Cl(-)-HCO3- exchangers

1988 ◽  
Vol 255 (6) ◽  
pp. C857-C869 ◽  
Author(s):  
G. Boyarsky ◽  
M. B. Ganz ◽  
R. B. Sterzel ◽  
W. F. Boron
Keyword(s):  
Mesangial Cells ◽  
Ph Regulation ◽  
Large Fraction ◽  
Preceding Paper ◽  
Disulfonic Acid ◽  
Glomerular Mesangial Cells ◽  
Total Acid ◽  
Small Component ◽  
Rate Of Recovery ◽  
Acid Extrusion

We used the pH-sensitive dye 2,7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF) to further characterize the mechanisms of intracellular pH (pHi) regulation in renal mesangial cells. In the accompanying paper [Am. J. Physiol. 255 (Cell Physiol. 24): C844-C856, 1988], we showed that acid extrusion from mesangial cells is mediated by both an ethylisopropylamiloride (EIPA)-sensitive Na+-H+ exchanger and a 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS)-sensitive-HCO3(-)-dependent mechanism. In this study, we examined the ionic dependencies of pHi-regulatory mechanisms in the presence of CO2-HCO3-. We found that in CO2-HCO3-, approximately 90% of the net acid extrusion occurring during recovery from an acid load is blocked by removing external Na+. Short-term (less than 15 min) removal of external Cl- has little effect on the rate of recovery in CO2-HCO3-. In contrast longer periods of external Cl- removal (1-2 h) blocks 40-60% of the rate of recovery, which is consistent with the hypothesis that a large fraction of the SITS-sensitive-HCO3(-)-dependent recovery mechanism described in the preceding paper is also Na+- and Cl(-)-dependent. Therefore, this Cl(-)-dependent component is probably mediated by a Na+-dependent Cl(-)-HCO3- exchanger. As much as 16% of total acid extrusion is insensitive to EIPA and long-term Cl- removal but is blocked by SITS. Thus either 1-2 h of Cl- removal is insufficient to wash out all internal Cl-, or a small component of acid extrusion is mediated by a Cl(-)-independent mechanism, such as the electrogenic Na+/HCO3- cotransporter. We also studied the effect on pHi of the removal and readdition of external Cl-, observing pHi changes consistent with the existence of a Na+-independent Cl(-)-HCO3- exchanger, which would presumably function as an acid loader. In contrast to the Na+-H+ exchanger and Na+-dependent Cl(-)-HCO3- exchanger, which are stimulated at low pHi, the Cl(-)-HCO3- exchanger is stimulated at high pHi. Thus the acid-extruding and acid-loading mechanisms have opposite pHi dependencies.

scholarly journals Regulation of Intracellular pH in Single Rat Cortical Neurons in vitro: A Microspectrofluorometric Study

1993 ◽  
Vol 13 (5) ◽  
pp. 827-840 ◽  
Author(s):  
Yibing Ou-Yang ◽  
Pekka Mellergård ◽  
Bo K. Siesjö
Keyword(s):  
Steady State ◽  
Intracellular Ph ◽  
Cortical Neurons ◽  
Ph Sensitive ◽  
Disulfonic Acid ◽  
Extrusion Rate ◽  
Rat Cortical Neurons ◽  
Acid Extrusion

Intracellular pH (pHi) and the mechanisms of pHi regulation in cultured rat cortical neurons were studied with microspectrofluorometry and the pH-sensitive fluorophore 2′,7′-bis(carboxyethyl)-5,6-carboxyfluorescein. Steady-state pHi was 7.00 ± 0.17 (mean ± SD) and 7.09 ± 0.14 in nominally HCO3− -free and HCO3−-containing solutions, respectively, and was dependent on extracellular Na+ and Cl−. Following an acid transient, induced by an NH1 prepulse or an increase in CO2 tension, pHi decreased and then rapidly returned to baseline, with an average net acid extrusion rate of 2.6 and 2.8 mmol/L/min, in nominally HCO3− -free and HCO3− -containing solutions, respectively. The recovery was completely blocked by removal of extracellular Na+ and was partially inhibited by amiloride or 5- N-methyl- N-isobutylamiloride. In most cells pHi recovery was completely blocked in the presence of harmaline. The recovery of pHi was not influenced by addition of 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) or removal of Cl−. The rapid regulation of pHi seen following a transient alkalinization was not inhibited by amiloride or by removal of extracellular Na+, but was partially inhibited by DIDS and by removal of extracellular Cl−. The results are compatible with the presence of at least two different pHi-regulating mechanisms: an acid-extruding Na+/H+ antiporter, possibly consisting of different subtypes, and a passive Cl−/HCO3− exchanger, mediating loss of HCO3− from the cell.

scholarly journals Intracellular pH Regulation in Cultured Astrocytes from Rat Hippocampus

1997 ◽  
Vol 110 (4) ◽  
pp. 453-465 ◽  
Author(s):  
Mark O. Bevensee ◽  
Regina A. Weed ◽  
Walter F. Boron
Keyword(s):  
Intracellular Ph ◽  
Ph Regulation ◽  
Disulfonic Acid ◽  
Bath Solution ◽  
Major Cation ◽  
Cultured Astrocytes ◽  
Buffering Power ◽  
Acid Load ◽  
Acid Extrusion ◽  
Best Fit

We studied the regulation of intracellular pH (pHi) in single cultured astrocytes passaged once from the hippocampus of the rat, using the dye 2′,7′-biscarboxyethyl-5,6-carboxyfluorescein (BCECF) to monitor pHi. Intrinsic buffering power (βI) was 10.5 mM (pH unit)−1 at pHi 7.0, and decreased linearly with pHi; the best-fit line to the data had a slope of −10.0 mM (pH unit)−2. In the absence of HCO3−, pHi recovery from an acid load was mediated predominantly by a Na-H exchanger because the recovery was inhibited 88% by amiloride and 79% by ethylisopropylamiloride (EIPA) at pHi 6.05. The ethylisopropylamiloride-sensitive component of acid extrusion fell linearly with pHi. Acid extrusion was inhibited 68% (pHi 6.23) by substituting Li+ for Na+ in the bath solution. Switching from a CO2/HCO3−-free to a CO2/HCO3−-containing bath solution caused mean steady state pHi to increase from 6.82 to 6.90, due to a Na+-driven HCO3− transporter. The HCO3−-induced pHi increase was unaffected by amiloride, but was inhibited 75% (pHi 6.85) by 400 μM 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS), and 65% (pHi 6.55–6.75) by pretreating astrocytes for up to ∼6.3 h with 400 μM 4-acetamide-4′-isothiocyanatostilbene-2,2′-disulfonic acid (SITS). The CO2/HCO3−-induced pHi increase was blocked when external Na+ was replaced with N-methyl-d-glucammonium (NMDG+). In the presence of HCO3−, the Na+-driven HCO3− transporter contributed to the pHi recovery from an acid load. For example, HCO3− shifted the plot of acid-extrusion rate vs. pHi by 0.15–0.3 pH units in the alkaline direction. Also, with Na-H exchange inhibited by amiloride, HCO3− increased acid extrusion 3.8-fold (pHi 6.20). When astrocytes were acid loaded in amiloride, with Li+ as the major cation, HCO3− failed to elicit a substantial increase in pHi. Thus, Li+ does not appear to substitute well for Na+ on the HCO3− transporter. We conclude that an amiloride-sensitive Na-H exchanger and a Na+-driven HCO3− transporter are the predominant acid extruders in astrocytes.

Analysis of Cl- -HCO3(-) exchange during recovery from intracellular acidosis in cardiac Purkinje strands

1984 ◽  
Vol 246 (5) ◽  
pp. C391-C400 ◽  
Author(s):  
B. Vanheel ◽  
A. de Hemptinne ◽  
I. Leusen
Keyword(s):  
Steady State ◽  
Membrane Permeability ◽  
Intracellular Ph ◽  
Significant Role ◽  
Exchange Mechanism ◽  
Disulfonic Acid ◽  
Intracellular Acidification ◽  
Intracellular Acidosis ◽  
Acid Extrusion

The possible role of a Cl- -HCO3(-) exchange mechanism in the recovery from intracellular acidosis of isolated cardiac Purkinje strands was investigated. Intracellular pH (pHi) was measured using double-barreled pH-sensitive microelectrodes. Acidifications were produced by withdrawing 20 meq NH+4 from the superfusate. Experiments were performed in normal CO2-HCO3(-)-buffered, in HCO3(-)free, and in Cl-free solutions and also in the presence of 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), a blocker of Cl--HCO3(-) exchange. In the absence of external HCO3(-), the apparent rate of acid extrusion following induced acidification was only slightly decreased, but the observed effect does not necessarily imply the intervention of a Cl--HCO3(-) exchange mechanism. SITS had little effect on the response to acidification. In zero-Cl- solutions, recovery of pHi from acidosis was not impaired. These observations suggest that in Purkinje fibers, [Cl-]i-[HCO3(-)]o exchange plays no significant role in recovery from intracellular acidification. Moreover, additional evidence is presented in favor of a passive HCO3(-) efflux at steady-state pHi in the normal superfusate. The apparent membrane permeability to HCO-3 was estimated to be 3.2 X 10(-8) cm X s-1.

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