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W F Boron

Publications and source records attributed to W F Boron.

At least 19 recordsLinked to original sources
PubMed1992

Na(+)-dependent Cl-HCO3 exchange in the squid axon. Dependence on extracellular pH.

Intracellular pH (pHi) in squid giant axons recovers from acid loads by means of a Na(+)-dependent Cl-HCO3 exchanger, the actual mechanism of which might be exchange of: (i) external Na+ and HCO3- for internal Cl- and H+, (ii) Na+ plus two HCO3- for Cl-, (iii) Na+ and CO3= for Cl-, or (iv) the NaCO3- ion pair for Cl-. Here we examine sensitivity of transport to changes of extracellular pH (pHo) in the range 7.1-8.6. We altered pHo in four ways, using: (i) classical "metabolic" disturbances in which we varied [HCO3-]o, [NaCO3-]o, and [CO3=]o at a fixed [CO2]o; (ii) classical "respiratory" disturbances in which we varied [CO2]o, [NaCO3-]o, and [CO3=]o at a fixed [HCO3-]o; (iii) novel mixed-type acid-base disturbances in which we varied [HCO3-]o and [CO2]o at a fixed [CO3=]o and [NaCO3-]o; and (iv) a second series of novel mixed-type disturbances in which we varied [CO2]o, [CO3=]o, and [Na+]o at a fixed [HCO3-]o and [NaCO3-]o. Axons (initial pHi approximately 7.4) were internally dialyzed with a pH 6.5 solution containing 400 mM Cl- but no Na+. After pHi, measured with a glass microelectrode, had fallen to approximately 6.6, dialysis was halted. The equivalent acid extrusion rate (JH) was computed from the rate of pHi recovery (i.e., increase) in the presence of Na+ and HCO3-. When pHo was varied by method (i), which produced the greatest range of [CO3=]o and [NaCO3-]o values, JH increased with pHo in a sigmoidal fashion; the relation was fitted by a pH titration curve with a pK of approximately 7.7 and a Hill coefficient of approximately 3.0. With method (ii), which produced smaller changes in [CO3=]o and [NaCO3-]o, JH also increased with pHo, though less steeply. With method (iii), which involved changes in neither [CO3=]o nor [NaCO3-]o, JH was insensitive to pHo changes. Finally, with method (iv), which involved changes in neither [HCO3-] nor [NaCO3-]o, but reciprocal changes in [CO3=]o and [Na+]o, JH also was insensitive to pHo changes. We found that decreasing pHo from 8.6 to 7.1 caused the apparent Km for external HCO3- ([Na+]o = 425 mM) to increase from 1.0 to 26.7 mM, whereas Jmax was relatively stable. Decreasing pHo from 8.6 to 7.4 caused the apparent Km values for external Na+ ([HCO3-]o = 48 mM) to increase from 8.6 to 81 mM, whereas Jmax was relatively stable.(ABSTRACT TRUNCATED AT 400 WORDS)

Acid-Base Equilibrium↗
PubMed1992

Role of G proteins in stimulation of Na-H exchange by cell shrinkage.

Many cells respond to shrinkage by stimulating specific ion transport processes (e.g., Na-H exchange). However, it is not known how the cell senses this volume change, nor how this signal is transduced to an ion transporter. We have studied the activation of Na-H exchange in internally dialyzed barnacle muscle fibers, measuring intracellular pH (pHi) with glass microelectrodes. When cells are dialyzed to a pHi of approximately 7.2, Na-H exchange is active only in shrunken cells. We found that the shrinkage-induced stimulation of Na-H exchange, elicited by increasing medium osmolality from 975 to 1,600 mosmol/kgH2O, is inhibited approximately 72% by including in the dialysis fluid 1 mM guanosine 5'-O-(2-thiodiphosphate). The latter is an antagonist of G protein activation. Even in unshrunken cells, Na-H exchange is activated by dialyzing the cell with 1 mM guanosine 5'-O-(3-thiotriphosphate), which causes the prolonged activation of G proteins. Activation of Na-H exchange is also elicited in unshrunken cells by injecting cholera toxin, which activates certain G proteins. Neither exposing cells to 100 nM phorbol 12-myristate 13-acetate nor dialyzing them with a solution containing 20 microM adenosine 3',5'-cyclic monophosphate (cAMP) (or 50 microM dibutyryl cAMP) plus 0.5 mM 3-isobutyl-1-methylxanthine substantially stimulates the exchanger. Thus our data suggest that a G protein plays a key role in the transduction of the shrinkage signal to the Na-H exchanger via a pathway that involves neither protein kinase C nor cAMP.

Animals↗
PubMed1992

Activation of Na-H exchange by intracellular lithium in barnacle muscle fibers.

We internally dialyzed single barnacle muscle fibers (BMF) for 90 min with a dialysis fluid (DF) containing no Na+ and either 0 or 100 mM Li+ and measured intracellular pH (pHi) with a microelectrode. During dialysis, the pH 8.0 artificial seawater (ASW) contained neither Na+ nor HCO3-. After we halted dialysis with a Li(+)-free/low-pH DF and allowed pHi to stabilize at approximately 6.8, adding 440 mM Na(+)-10 mM HCO3- to the ASW caused pHi to recover rapidly and stabilize at 7.32. In contrast, when the DF contained 100 mM Li+, pHi stabilized at 7.49. In fibers dialyzed to a pHi of approximately 7.2, Li+ stimulated a component of acid extrusion that was dependent on Na+ but not affected by SITS. Thus Li+ activates a Na(+)-dependent acid-extrusion mechanism other than the well characterized Na(+)-dependent Cl-HCO3 exchanger. To study the Li(+)-activated mechanism, we minimized Na(+)-dependent Cl-HCO3 exchange by raising pHDF to 7.35 and pretreated BMFs with SITS. We found that dialysis with Li+ elicits a Na(+)-dependent pHi increase that is largely blocked by amiloride, consistent with the hypothesis that Li+ activates a latent Na-H exchanger even at a normal pHi. In the absence of Li+, the Na-H exchanger is relatively inactive at pHi 7.35 (net acid-extrusion rate, Jnet = 9.5 microM/min) but modestly stimulated by reducing pHi to 6.8 (Jnet = 64 microM/min). In the presence of Li+, the Na-H exchanger is very active at pHi values of both 7.35 (Jnet = 141 microM/min) and 6.8 (Jnet = 168 microM/min). Thus Li+ alters the pHi sensitivity of the Na-H exchanger. Because the Na-H exchanger is only approximately 6% as active as the Na(+)-dependent Cl-HCO3 exchanger in the absence of Li+ at a pHi of approximately 6.8, we suggest that the major role of the Na-H exchanger may not be in pHi regulation but in another function such as cell-volume regulation.

Acids↗
PubMed1991

Effect of diabetes on Na(+)-H+ exchange by single isolated hepatocytes.

We used the fluorescent dye 2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) to examine intracellular pH (pHi) regulation in single hepatocytes isolated from control rats and rats with either spontaneous or drug-induced diabetes mellitus (DM). In the absence of CO2-HCO3-, both control and DM cells recovered from cellular acid loads applied by the NH4+ prepulse technique. Because the pHi recovery was blocked by either Na+ withdrawal or ethylisopropylamiloride in both control and DM cells, it was presumably mediated by Na(+)-H+ exchange. In the control cells, the pHi threshold above which the rate of change of pHi (dpHi/dt) was zero was 7.06, and the slope of the dpHi/dt-pHi relationship was -0.030 s-1. In the DM cells, the pHi threshold was 7.22 and the slope was -0.017 s-1. Thus, at pHi values below approximately 6.9, the pHi recovery was slower in the DM cells. Inasmuch as we observed no difference in the cellular buffering power between control and DM cells, diabetes inhibits Na(+)-H+ exchange within this low pHi range. At pHi values above approximately 6.9, however, Na(+)-H+ exchange was apparently stimulated by diabetes. Thus diabetes induces two distinct alterations of Na(+)-H+ exchange, an alkaline shift in pHi threshold and decrease in slope. Treatment of diabetic rats with insulin for 48 h restored both Na(+)-H+ exchange parameters to normal. On the other hand, insulin added in vitro to DM cells for 2-5 h shifted the threshold toward the control value without affecting the slope, thus leading to a further inhibition of Na(+)-H+ exchange over the entire pHi range.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Intracellular-pH dependence of Na-H exchange and acid loading in quiescent and arginine vasopressin-activated mesangial cells.

We studied intracellular pH (pHi) regulation in the absence of HCO3- in single mesangial cells (MCs) with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(and -6)carboxyfluorescein. Our approach was to acid load the cells by an NH+4 prepulse and to monitor the subsequent pHi recovery. Previous work on MCs and other cells has shown that the recovery is prevented by adding ethylisopropyl amiloride (EIPA) or removing Na+ before the recovery begins, suggesting that at low pHi only Na-H exchange contributes to the recovery. This conclusion is often extrapolated to the entire pHi range. To test this, we interrupted the recovery with EIPA at various pHi values, finding that EIPA unmasked a background acidification that was negligible at pHi less than approximately 6.7 but increased steeply at higher pHi values. Correcting the total recovery rate for this EIPA-insensitive component, we found that the EIPA-sensitive (Na-H exchange) rate fell steeply with increasing pHi between 6.3 and 6.7 but was relatively pHi insensitive between 6.7 and 7.2. Thus, the recovery halts as pHi approaches approximately 7.2 not so much because Na-H exchange slows, but because acid loading accelerates. Applying the mitogen arginine vasopressin (AVP; 100 nM) caused a rapid pHi decrease of approximately 0.4, followed by a slower increase to a level approximately 0.15 higher than the initial pHi. Coincident with this biphasic change in pHi was a biphasic change in Na-H exchange kinetics. In the early phase (i.e., pHi recovery commencing approximately 8 min after AVP addition), AVP linearized the pHi dependence of the exchanger; its rate was unaffected by AVP at pHi less than approximately 6.7 but was progressively inhibited at higher pHi values. In the later phase (i.e., pHi recovery commencing approximately 14 min after AVP addition), AVP shifted this linear pHi dependence in the alkaline direction; the exchanger was stimulated at pHi less than 6.9 but was modestly inhibited at higher pHi values (i.e., in the physiological range). At all times, AVP greatly inhibited background acid loading. Thus, AVP raises steady-state pHi not because Na-H exchange is stimulated but because, although the exchanger is inhibited, acid loading is inhibited even more.

Amiloride↗
PubMed1990

Angiotensin II stimulates both Na(+)-H+ exchange and Na+/HCO3- cotransport in the rabbit proximal tubule.

Angiotensin II (AII) is a potent stimulus for HCO3- reabsorption in the rat proximal tubule in vivo. To determine the ionic mechanism of increased HCO3- reabsorption, we have examined the effect of AII on luminal Na(+)-H+ exchange and basolateral Na+/HCO3- cotransport in perfused S1 proximal tubules isolated from superficial nephrons of the rabbit kidney. Transporter activity was assessed by removing Na+ from both luminal and basolateral (i.e., bath) solutions and determining the rate at which intracellular pH (pHi) increased after Na+ was returned to only the lumen or only the bath. pHi was measured with the pH-sensitive fluorescent dye 2', 7'-bis(2-carboxyethyl)-5(and 6)-carboxyfluorescein. We found that basolateral administration of 1 nM AII not only increased the rate of luminal Na(+)-H+ exchange approximately 3.5-fold but also increased the rate of basolateral Na+/HCO3- cotransport approximately 2.5-fold. 5-(N-Ethyl-N-isopropyl)amiloride (50 microM) blocked luminal Na(+)-H+ exchange before and after stimulation by AII but had no effect on basolateral Na+/HCO3- cotransport. Conversely, 4,4'-diisothiocyanato-2,2'-stilbenedisulfonate (50 microM) blocked basolateral Na+/HCO3- cotransport before and after AII but had no effect on luminal Na(+)-H+ exchange. Our data thus indicate that, at least under the conditions of our assay, AII independently stimulates the transporters responsible for both the luminal and basolateral steps of transepithelial HCO3- reabsorption.

Angiotensin II↗
PubMed1990

Intracellular pH regulation in rabbit S3 proximal tubule: basolateral Cl-HCO3 exchange and Na-HCO3 cotransport.

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.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1990

Effects of mitogens and other agents on rat mesangial cell proliferation, pH, and Ca2+.

We investigated effects of various agents on proliferation, intracellular pH (pHi), and intracellular calcium [( Ca2+]i) of rat mesangial cells (MCs) in early passages (2-5). Serum-starved MCs incubated in HCO3- were exposed to one of the following: fetal calf serum (FCS), serotonin, angiotensin II (ANG II), arginine vasopressin (AVP), bombesin (Bom), bradykinin (BK), epidermal growth factor (EGF), epinephrine (Epi), interleukin 1 (IL-1), norepinephrine (NE), neuropeptide Y, oxytocin, substance P (SP), platelet-derived growth factor, or 12-O-tetradecanoylphorbol-13-acetate (TPA). We assessed DNA synthesis from [3H]thymidine uptake during exposure to test agent. All agents except ANG II, NE, Bom, and SP were mitogenic. When MCs were incubated in a HCO3(-) -free N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium, maximal mitogenic responses to FCS, AVP, and EGF were 41, 44, and 55% (P less than 0.01) lower, respectively, than those in presence of HCO3-. In absence of HCO3-, agents other than BK and IL-1 produced a biphasic pHi response characterized by a transient acidification followed by a prolonged alkalinization that was both Na(+)-dependent and amiloride-sensitive. In presence of HCO3-, agents produced only a small and gradual acidification, except for IL-1 and Epi. Addition of all agonists except IL-1, EGF, and TPA produced significant transient increases in [Ca2+]i, the magnitudes of which were similar in HCO3- and non-HCO3- buffers. These results demonstrate that, in presence of HCO3-, agents (i.e., NE and ANG II) can produce typical [Ca2+]i transients and still not cause MC proliferation. Conversely, an agent may cause proliferation without eliciting a short-term change in either [Ca2+]i or pHi (i.e., IL-1), a change in [Ca2+]i but not pHi (i.e., Epi), or a change in pHi but not [Ca2+]i (i.e., TPA). Thus, at least for MCs, proliferation in HCO3- can be dissociated from early agonist-induced changes in pHi and [Ca2+]i.

Animals↗
PubMed1989

Arginine vasopressin enhances pHi regulation in the presence of HCO3- by stimulating three acid-base transport systems.

Growth factors raise intracellular pH (pHi) by stimulating Na+/H+ exchange in the absence of HCO3-. In mutant cells that lack the Na+/H+ exchange activity, this alkalinization does not occur, and the cells do not proliferate without artificial elevation of pHi. It has therefore been widely suggested that an early pHi increase is a necessary signal for mitogenesis. In the presence of HCO3- however, growth factors fail to raise pHi in A431 cells, renal mesangial cells and 3T3 fibroblasts. In mesangial cells, arginine vasopressin (AVP) raises pHi in the absence of HCO3-, but lowers it when HCO3- is present; growth is stimulated under both conditions. We report here that, in the presence of HCO3-, AVP stimulates two potent HCO3- transporters, as well as the Na+/H+ exchanger. These are the Na+-dependent and Na+-independent Cl-/HCO3- exchangers. Our results indicate that AVP causes acidification in the presence of HCO3- because, at the resting pHi, it stimulates Na+-independent Cl-/HCO3- exchange (which lowers pHi) more than it stimulates the sum of Na+/H+ exchange and Na+-dependent Cl-/HCO3- exchange (both of which raise pHi). The stimulation of three acid-base transporters by the growth factor AVP greatly enhances the ability of the cell to regulate pHi.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1989

Intracellular pH-regulating mechanism of the squid axon. Interaction between DNDS and extracellular Na+ and HCO3-.

Intracellular pH (pHi) of the squid axon is regulated by a stilbenesensitive transporter that couples the influx of Na+ and HCO3- (or the equivalent) to the efflux of Cl-. According to one model, the extracellular ion pair NaCO3- exchanges for intracellular Cl-. In the present study, the ion-pair model was tested by examining the interaction of the reversible stilbene derivative 4,4'-dinitrostilbene-2,2'-disulfonate (DNDS) with extracellular Na+ and HCO3-. Axons (initial pHi approximately 7.4) were internally dialyzed with a pH 6.5 solution containing 400 mM Cl- but no Na+. After pHi, as measured with a glass microelectrode, had fallen to approximately 6.6, dialysis was halted. In the presence of both external Na+ and HCO3- (pHo = 8.0, 22 degrees C), pHi increased due to the pHi-regulating mechanism. At a fixed [Na+]o of 425 mM and [HCO3-]o of 12 mM, DNDS reversibly reduced the equivalent acid-extrusion rate (JH) calculated from the rate of pHi recovery. The best-fit value for maximal inhibition was 104%, and for the [DNDS]o at half-maximal inhibition, 0.3 mM. At a [Na+]o of 425 mM, the [HCO3-]o dependence of JH was examined at 0, 0.1, and 0.25 mM DNDS. Although Jmax was always approximately 20 pmol cm-2 s-1, Km(HCO3-) was 2.6, 5.7, and 12.7 mM, respectively. Thus, DNDS is competitive with HCO3-. At a [HCO3-]o of 12 mM, the [Na+]o dependence of JH was examined at 0 and 0.1 mM DNDS. Although Jmax was approximately 20 pmol cm-2 s-1 in both cases, Km(Na+) was 71 and 179 mM, respectively. At a [HCO3-]o of 48 mM, Jmax was approximately 20 pmol cm-2 s-1 at [DNDS]o levels of 0, 0.1, and 0.25 mM. However, Km(Na+) was 22, 45, and 90 mM, respectively. Thus, DNDS (an anion) is also competitive with Na+. The results are consistent with simple competition between DNDS and NaCO3-, and place severe restrictions on other kinetic models.

Animals↗
PubMed1989

Depolarization-induced alkalinization in proximal tubules. I. Characteristics and dependence on Na+.

We used intracellular pH-sensitive and voltage microelectrodes to examine the effects of depolarization on intracellular pH (pHi) in isolated perfused proximal tubules from the tiger salamander Ambystoma tigrinum. Tubules were depolarized by raising [K+] in the bath (b) or lumen (l), or by adding Ba2+ (1 mM) to the bath or lumen, always in nominally HCO3-free solutions. Increasing [K+]b from 2.5 to 50 mM caused the basolateral membrane to depolarize by an average of 45 mV, and pHi to increase by 0.23 over 3 min. Similar alkalinization was observed when basolateral Ba2+ (1 mM) was used to depolarize the cell at constant extracellular [K+], suggesting that the alkalinization observed during exposure to elevated [K+]b results from depolarization rather than an increase in [K+]b. The initial rate of depolarization-induced alkalinization (DIA) was proportional to the magnitude of the depolarization, regardless of whether tubules were depolarized by elevated [K+]b, elevated [K+]l, or by basolateral Ba2+. An exception was the initial rate of the alkalinization caused by 1 mM luminal Ba2+, which was more than 10-fold greater than that predicted from the depolarization. The voltage and pHi responses to basolateral Ba2+ were smaller in some tubules than others, as were the responses to elevated [K+]l. Tubules with small responses to 1 mM [Ba2+]b had large responses to 50 mM [K+]l, whereas tubules with large responses to 1 mM [Ba2+]b had small responses to 50 mM [K+]l. This variability can be accounted for by differences in the luminal K+ conductance. The DIA was partially inhibited by removal of Na+ from only the lumen or only the bath, but completely inhibited by bilateral Na+ removal. We conclude that the depolarization-induced alkalinization results from additive effects of Na+-dependent processes at both the luminal and basolateral membranes.

Ambystoma↗
PubMed1989

Depolarization-induced alkalinization in proximal tubules. II. Effects of lactate and SITS.

Intracellular pH and voltage microelectrodes were used to further characterize the depolarization-induced alkalinization (DIA) observed in isolated perfused proximal tubules of the tiger salamander Ambystoma tigrinum. Tubules were depolarized by raising basolateral [K+] from 2.5 to 50 mM. The solutions were air equilibrated and nominally HCO3- free (estimated [HCO3-] = 0.2 mM). In the preceding study we showed that the DIA is partially blocked by removal of Na+ from only the lumen or only the bath, but completely blocked by bilateral Na+ removal. In the present study we found that bilateral amiloride (1 mM) had no effect on the DIA, suggesting that Na-H exchange is not involved. In contrast, basolateral 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) (0.5 mM) partially blocked the DIA, presumably due to inhibition of one or more of three SITS-sensitive basolateral transporters present in amphibian proximal tubules: electrogenic Na-HCO3 cotransport, Na-dependent Cl-HCO3 exchange, and H-lactate cotransport. Bilateral removal of all organic substrates, or of only lactate (Lac-) also blocked the DIA partially. As shown elsewhere (A. W. Siebens, and W. F. Boron, J. Gen. Physiol. 90: 799-831, 1987), in the absence of depolarization, luminal Lac- causes a pHi increase due to luminal Lac- entry via a Na-Lac cotransporter, followed by basolateral Lac- exit via an H-Lac cotransporter sensitive to alpha-cyano-4-hydroxycinnamate (CHC). Three lines of evidence indicate that this Na-Lac/H-Lac mechanism is involved in the DIA. 1) As noted previously, the DIA is partially blocked by luminal Na+ removal. 2) With the DIA partially blocked by basolateral SITS, removal of Lac- from only the lumen blocks the remainder of the DIA. 3) Basolateral CHC partially blocks the DIA. Our data suggest that the DIA is mediated by at least two additive mechanisms, a basolateral transporter that is SITS sensitive and Na+ dependent, and the Na-Lac/H-Lac transport system.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1989

Effects of acetate on luminal acidification processes in the S3 segment of the rabbit proximal tubule.

We determined that, in the nominal absence of HCO-3, acetate (Ac-) doubles luminal acidification in the S3 segment of the rabbit proximal tubule. This stimulation had two components, one that was dependent on Na+ and luminal Ac- and a second that was independent of Na+ but dependent on basolateral Ac-. In the presence of 25 mM HCO-3, Ac- did not stimulate acid secretion (i.e., HCO-3 reabsorption), but actually inhibited it. The inhibition was 35% with bilateral Ac- and 15% with basolateral Ac-. The effects of Ac- were reversible both in the absence and presence of HCO-3, and are present at concentrations as low as 1 mM. We conclude that acetate (i.e., monocarboxylates) has a significant effect on luminal acidification processes both in the presence and absence of HCO-3.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1989

Basolateral sodium-coupled acid-base transport mechanisms of the rabbit proximal tubule.

We studied Na+-coupled acid-base transport at the basolateral membrane of single, isolated, perfused rabbit proximal tubules by monitoring the time course of intracellular pH (pHi). The latter was determined using a microspectrofluorometric apparatus to alternatively excite the pH-sensitive fluorescent dye 2',7'-bis-2-carboxyethyl-5(and -6)-carboxyfluorescein (BCECF) at 440 and 490 nm, while the fluorescence emission, was measured at 530 nm. All experiments were conducted in the nominal absence of HCO-3 S1, S2, and S3 segments from both superficial and juxtamedullary nephrons were examined individually. We found that removing Na+ from both the lumen and bath (i.e., basolateral solution) caused pHi to fall from 7.24 to 6.75 in the superficial S1 segment (SS1), from 7.14 to 6.67 in the SS2, and from 7.09 to 6.69 in the SS3. Similarly, in juxtamedullary nephrons (J), bilateral Na+ removal caused pHi to fall from 7.25 to 6.76 in the JS1, from 7.16 to 6.71 in the JS2, and from 7.10 to 6.75 in the JS3. In all six proximal tubule subtypes, returning Na+ to the bath caused pHi to recover (i.e., increase). 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 50 microM), an inhibitor of HCO-3 transport systems, blocked this Na+-dependent pHi recovery in all three superficial subtypes and the JS3 but had no effect in either the JS1 or JS2. On the other hand, 50 microM ethylisopropyl amiloride (EIPA), an inhibitor of Na-H exchange, blocked the Na+-dependent pHi recovery in the JS1 and JS2 but had no effect in the JS3 or any of the superficial subtypes.(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗