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R C Thomas

Publications and source records attributed to R C Thomas.

At least 37 records · Page 2Linked to original sources
PubMed1996

Translocation of the retinoblastoma gene product during mitosis.

This study reports the immunocytochemical localization of the retinoblastoma gene product within synchronized normal human keratinocytes. Data suggest that mitotic spindles function in the transport of the retinoblastoma tumor suppressor gene product during cell division. A diffuse anti-pRB reactivity was detected within the nuclei of G1-phase keratinocytes, although staining was not evident within the nucleoli. During S-phase and G2-phase the anti-pRB reactivity was localized to discrete regions within the nuclear compartment. The anti-pRB reactivity of M-phase cells was localized to the mitotic spindles and microtubule nucleation centers. Immunoprecipitation and Western blotting of the pRB antigen from synchronized keratinocytes showed that the apparent polypeptide molecular weight of pRB increased from 105 kDa during G1-phase to 115 kDa during M-phase. Immunoprecipitation of the pRB antigen from mitotic spindles resulted in the coprecipitation of two polypeptides with apparent polypeptide molecular weights of 115 and 50 kDa. Western blotting of the immunoprecipitates from purified keratinocyte mitotic spindles showed that beta-tubulin was the 50-kDa polypeptide associated with hyperphosphorylated pRB.

Biological Transport↗
PubMed1996

Relationship between intracellular calcium and its muffling measured by calcium iontophoresis in snail neurones.

1. We have measured intracellular free calcium ion concentration ([Ca2+]i) with fura-2, and intracellular chloride with chloride-sensitive microelectrodes, in voltage-clamped snail neurones. By making iontophoretic injections of CaCl2 we have investigated calcium muffling, the sum of the processes which minimize the calcium transient, at different values of [Ca2+]i. 2. By injection of calcium into cell-sized droplets of buffer we measured the calcium transport index. It was stable over the range pCa 6-7.4 (0.48 +/- 0.06 measured at pCa 6.70 +/- 0.12, n = 5). 3. Measurement of intracellular chloride activity during a series of fura-2-KCl pressure injections revealed a nearly linear relationship between fura-2 Ca(2+)-insensitive fluorescence and the sum of the increments in intracellular chloride. This allowed us to calculate the intracellular fura-2 concentration ([fura-2]i). 4. The rate of recovery of [Ca2+]i following a depolarization-induced load was increased by low [fura-2]i (10-20 microM) but decreased by higher [fura-2]i (40-80 microM). These effects are consistent with the addition of a mobile buffer to the cytoplasm. 5. Iontophoresis of Ca2+ at various membrane potentials allowed us to calculate the intracellular calcium muffling power (the amount of calcium required to cause a transient tenfold increase in [Ca2+]i per unit volume) and calcium muffling ratio (number of Ca2+ ions injected divided by the maximum increase in [Ca2+]i per unit volume) at different values of [Ca2+]i. 6. Calcium muffling power at resting [Ca2+]i was approximately 40 microM Ca2+ (pCa unit)-1, (about 250 times less than for hydrogen ions). It increased linearly about fivefold with [Ca2+]i over the range 20-120 nM (10 cells, 153 measurements) and therefore exponentially with decreasing pCa. 7. The calcium muffling ratio appeared to be constant (361 +/- 14, n = 10 cells, 130 measurements) over the range 20-120 nM Ca2+. 8. In three experiments we modelled the additional calcium buffering power produced by multiple pressure injections of fura-2 into voltage-clamped snail neurones. Back-extrapolation of the increases in calcium buffering power allowed us to calculate the calcium muffling power of the neurones. 9. Small increases in [fura-2]i (approximately 10 microM) significantly increased intracellular calcium muffling power in individual experiments. However, the variability among neurones in intracellular calcium muffling power was large enough to obscure the additional buffering produced by fura-2 in pooled experiments.

Animals↗
PubMed1996

Effects of injecting calcium-buffer solution on [Ca2+]i in voltage-clamped snail neurons.

We have investigated why fura-2 and Ca(2+)-sensitive microelectrodes report different values for the intracellular free calcium ion concentration ([Ca(2+)]i or its negative log, pCa(i)) of snail neurons voltage-clamped to -50 or -60 mV. Both techniques were initially calibrated in vitro, using calcium calibration solutions that had ionic concentrations similar to those of snail neuron cytoplasm. Pressure injections of the same solutions at resting and elevated [Ca(2+)]i were used to calibrate both methods in vivo. In fura-2-loaded cells these pressure injections generated changes in [Ca(2+)]i that agreed well with those expected from the in vitro calibration. Thus, using fura-2 calibrated in vitro, the average resting [Ca(2+)]i was found to be 38 nM (pCa(i) 7.42 +/- 0.05). With Ca(2+)-sensitive microelectrodes, the first injection of calibration solutions always caused a negative shift in the recorded microelectrode potential, as if the injection lowered [Ca2+]i. No such effects were seen on the fura-2 ratio. When calibrated in vivo the Ca(2+)-sensitive microelectrode gave an average resting [Ca2+]i of approximately 25 nM (pCa(i) 7.6 +/- 0.1), much lower than when calibrated in vitro. We conclude that [Ca(2+)]i in snail neurons is approximately 40 nM and that Ca(2+)-sensitive microelectrodes usually cause a leak at the point of insertion. The effects of the leak were minimized by injection of a mobile calcium buffer.

Animals↗
PubMed1996

Mouse monoclonal antipeptide antibodies specific for cholesteryl ester transfer protein (CETP).

A synthetic peptide whose amino acid sequence corresponds to residues 131-142 of human cholesteryl ester transfer protein (CETP) was used as an immunogen to generate a panel of monoclonal antibodies (MAbs) specific for the intact CETP molecule. Spleen cells from BALB/c mice immunized with the peptide conjugated with keyhole limpet hemocyanin (KLH) were fused with SP2/0 myeloma cells. Two MAbs that bound fixed peptide in an enzyme-linked immunoabsorbent assay (ELISA) were partially characterized regarding their specificity and biological activity. ATM192 of the IgG1 subclass and J16-14 of the IgG3 subclass were used in a Western blot assay as well as in the ELISA. We have also shown through the use of immunoprecipitation that ATM192 can remove CETP enzyme activity from human serum without destroying the enzyme's activity. We have also shown that the antibodies can bind CETP from rabbits. The specificity studies and the lack of inhibition of enzymatic activity suggest that the MAbs bind a structural area of the CETP molecule not a part of the active binding site of the enzyme. We conclude that these antibodies can be valuable as tools for studying CETP levels in human serum as well as in tissue homogenates from rabbits and humans.

Animals↗
PubMed1996

(Alkylamino) piperidine bis(heteroaryl)piperizine analogs are potent, broad-spectrum nonnucleoside reverse transcriptase inhibitors of drug-resistant isolates of human immunodeficiency virus type 1 (HIV-1) and select for drug-resistant variants of HIV-1IIIB with reduced replication phenotypes.

The (alkylamino)piperidine bis(heteroaryl)piperizines (AAP-BHAPs) are a new class of human immunodeficiency virus type 1 (HIV-1)-specific inhibitors which were identified by targeted screening of recombinant reverse transcriptase (RT) enzymes carrying key nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance-conferring mutations and NNRTI-resistant variants of HIV-1. Phenotypic profiling of the two most potent AAP-BHAPs, U-95133 and U-104489, against in vitro-selected drug-resistant HIV-1 variants carrying the NNRTI resistance-conferring mutation (Tyr->Cys) at position 181 of the HIV-1 RT revealed submicromolar 90% inhibitory concentration estimates for these compounds. Moreover, U-104489 demonstrated potent activity against BHA-P-resistant HIV-1MF harboring the Pro-236->Leu RT substitution and significantly suppressed the replication of clinical isolates of HIV-1 resistant to both delavirdine (BHAP U-90152T) and zidovudine. Biochemical and phenotypic characterization of AAP-BHAPresistant HIV-1IIIB variants revealed that high-level resistance to the AAP-BHAPs was mediated by a Gly-190->Glu substitution in RT, which had a deleterious effect on the integrity and enzymatic activity of virion-associated RT heterodimers, as well as the replication capacity of these resistant viruses.

Antiviral Agents↗
PubMed1995

Effects of low doses of caffeine on [Ca2+]i in voltage-clamped snail (Helix aspersa) neurones.

1. We have measured cytosolic free Ca2+ concentrations ([Ca2+]i) in voltage-clamped snail neurones using fura-2. Transient increases in [Ca2+]i were induced by depolarizing voltage steps of 20-60 mV for 0.1-10 s from a holding potential of -50 or -60 mV. 2. Low doses of caffeine, 0.2-1 mM, increased the size of the [Ca2+]i transients by both increasing the peak and producing an undershoot. 3. Ryanodine, an inhibitor of Ca2+ release from the intracellular Ca2+ stores, and cyclopiazonic acid (CPA), an inhibitor of the Ca(2+)-ATPase of the intracellular Ca2+ stores, both reduced the size of the [Ca2+]i transients and blocked the effects of caffeine on the transients. 4. The effects of caffeine and CPA were greater on transients produced by long, small, rather than short, large depolarizations. This suggests that calcium-induced calcium release (CICR) played a greater role in the [Ca2+]i increase resulting from longer, smaller depolarizations. 5. Increasing the extracellular pH from 7.5 to over 9, which inhibits the plasmalemmal Ca(2+)-H(+)-ATPase, increased the resting [Ca2+]i level. Depolarization-induced [Ca2+]i transients became much larger while the two effects of caffeine remained. CPA was ineffective at high pH. 6. In some experiments the increase in basal [Ca2+]i caused by alkaline pH was reduced by 0.2 or 0.5 mM caffeine. The increase in basal [Ca2+]i caused by maintained depolarization was reduced, after a transient increase, by 0.5 mM caffeine. Both reduction and increase were blocked by CPA. 7. We conclude that low doses of caffeine can increase uptake by intracellular Ca2+ stores. Caffeine could also release Ca2+ from ryanodine-insensitive Ca(2+)-ATPase-dependent stores as well as facilitating normal ryanodine-sensitive CICR.

Animals↗
PubMed1995

Simultaneous mutations at Tyr-181 and Tyr-188 in HIV-1 reverse transcriptase prevents inhibition of RNA-dependent DNA polymerase activity by the bisheteroarylpiperazine (BHAP) U-90152s.

The replacement of either Tyr-181 or Tyr-188 of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) by the corresponding HIV-2 RT amino acids Ile-181 or Leu-188 is known to result in active mutant enzymes (Y181I; Y188L) with virtual loss of sensitivity towards three structural classes of nonnucleoside RT inhibitors; L-697,661, nevirapine, and TIBO R82913. The bisheteroarylpiperazine (BHAP) U-90152S, a highly specific inhibitor (IC50, 0.29 +/- 0.01 microM) of HIV-1 RT, inhibited the recombinant Y181I and Y188L HIV-1 RT mutants with IC50 values of 3.6 +/- 0.15 microM and 0.71 +/- 0.02 microM, respectively. Construction and in vitro analysis of double mutants Y181I/Y188L and Y181C/Y188L of HIV-1 RT showed > 150-fold resistance to U-90152S. An HIV-2 RT mutant containing amino acids 176-190 from HIV-1 RT acquired full sensitivity to U-90152S (IC50, 0.26 +/- 0.01 microM). It is concluded that simultaneous mutations at Tyr-181 and Tyr-188 of HIV-1 RT promotes resistance to U-90152S.

Amino Acid Sequence↗
PubMed1995

Intracellular calcium and its sodium-independent regulation in voltage-clamped snail neurones.

1. We have used both Ca(2+)-sensitive microelectrodes and fura-2 to measure the intracellular free calcium ion concentration ([Ca2+]i or its negative log, pCai) of snail neurones voltage clamped to -50 or -60 mV. Using Ca(2+)-sensitive microelectrodes, [Ca2+]i was found to be approximately 174 nM and pCai, 6.76 +/- 0.09 (mean +/- S.E.M.; n = 11); using fura-2, [Ca2+]i was approximately 40 nM and pCai, 7.44 +/- 0.06 (mean +/- S.E.M., n = 10). 2. Depolarizations (1-20 s) caused an increase in [Ca2+]i which was abolished by removal of extracellular Ca2+, indicating that the rise in [Ca2+]i was due to Ca2+ influx through voltage-activated Ca2+ channels. 3. Caffeine (10-20 mM) caused an increase in [Ca2+]i in the presence or absence of extracellular Ca2+. The effects of caffeine on [Ca2+]i could be prevented by ryanodine. 4. Thapsigargin, an inhibitor of the endoplasmic reticulum Ca(2+)-ATPase, caused a small increase in resting [Ca2+]i and slowed the rate of recovery from Ca2+ loads following 20 s depolarizations. 5. Neither replacement of extracellular sodium with N-methyl-D-glucamine (NMDG), nor loading the cells with intracellular sodium, had any effect on resting [Ca2+]i or the rate of recovery of [Ca2+]i following depolarizations. 6. The mitochondrial uncoupling agent carbonyl cyanide m-chlorophenylhydrazone (CCmP) caused a small gradual rise in resting [Ca2+]i. Removal of extracellular sodium during exposure to CCmP had no further effect on [Ca2+]i. 7. Intracellular orthovanadate caused an increase in resting [Ca2+]i and prevented the full recovery of [Ca2+]i following small Ca2+ loads, but removal of extracellular sodium did not cause a rise in [Ca2+]i. We conclude that there is no Na(+)-Ca2+ exchanger present in the cell body of these neurones and that [Ca2+]i is maintained by an ATP-dependent Ca2+ pump.

Animals↗
PubMed1995

Mechanism of resistance to U-90152S and sensitization to L-697,661 by a proline to leucine change at residue 236 of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase.

Bisheteroarylpiperazines (BHAPs) are highly specific inhibitors of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). BHAP-resistant HIV-1 is sensitized to other classes of nonnucleoside RT inhibitors and this has been primarily attributed to a proline-to-leucine substitution at amino acid 236 (P236L) of HIV-1 RT. To understand the basis for the in vitro sensitization-resistance phenomenon, single base pair mutations at amino acid P236 in HIV-1 RT were introduced to obtain P236L, P236T, P236H, P236R, and P236A HIV-1 RT mutants. Active HIV-1 RT mutants H235W, D237T, and H235W/D237T/T240K, containing substitutions from HIV-2 RT, were also cloned, expressed, and purified. Three BHAPs (U-88204E, U-87201E, and U-90125S) and the pyridinone L-697,661 were selected to quantitatively assess the effects of these amino acid substitutions on sensitization to L-697,661 and resistance to the BHAPs. The HIV-1 RT mutants bearing single (H235W; D237T) or multiple (H235W/D237T/T240K) HIV-2 RT substitutions around the conserved P236 conferred little resistance or sensitization to these RT inhibitors. The inhibition profiles of the P236 HIV-1 RT mutants demonstrated a direct correlation between sensitization to L-697,661 and resistance to the BHAPs. These results suggest alterations in the shape of the binding pocket as the mechanism by which the P236L mutation confers resistance to the BHAPs and sensitization to L-697,661.

Amino Acid Sequence↗
PubMed1994

Kinetic studies with the non-nucleoside human immunodeficiency virus type-1 reverse transcriptase inhibitor U-90152E.

The bisheteroarylpiperazine U-90152E is a potent inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) and possesses excellent anti-HIV activity in HIV-1-infected lymphocytes grown in tissue culture. The compound inhibits both the RNA- and DNA-directed DNA polymerase functions of HIV-1 RT. Kinetic studies were carried out to elucidate the mechanism of RT inhibition by U-90152E. Michaelis-Menten kinetics, which are based on the establishment of a rapid equilibrium between the enzyme and its substrates, proved inadequate for the analysis of the experimental data. The data were thus analyzed using Briggs-Haldane kinetics, assuming that the reaction is ordered in that the template:primer binds to the enzyme first, followed by the addition of dNTP and that the polymerase is a processive enzyme. Based on these assumptions, a velocity equation was derived, which allows the calculation of all the essential forward and backward rate constants for the reactions occurring between the enzyme, its substrates and the inhibitor. The results obtained indicate that U-90152E acts exclusively as a mixed inhibitor with respect to the template: primer and dNTP binding sites for both the RNA- and DNA-directed DNA polymerase domains of the enzyme. The inhibitor shows a significantly higher binding affinity for the enzyme-substrate complexes than for the free enzyme and consequently does not directly impair the functions of the substrate binding sites. Therefore, U-90152E appears to impair an event occurring after the formation of the enzyme-substrate complexes, which involves either inhibition of the phosphoester bond formation or translocation of the enzyme relative to its template:primer following the formation of the ester bond.

Antiviral Agents↗
PubMed1994

Steady-state kinetic studies with the polysulfonate U-9843, an HIV reverse transcriptase inhibitor.

The tetramer of ethylenesulfonic acid (U-9843) is a potent inhibitor of HIV-1 RT* and possesses excellent antiviral activity at nontoxic doses in HIV-1 infected lymphocytes grown in tissue culture. Kinetic studies of the HIV-1 RT-catalyzed RNA-directed DNA polymerase activity were carried out in order to determine if the inhibitor interacts with the template primer or the deoxyribonucleotide triphosphate (dNTP) binding sites of the polymerase. Michaelis-Menten kinetics, which are based on the establishment of a rapid equilibrium between the enzyme and its substrates, proved inadequate for the analysis of the experimental data. The data were thus analyzed using steady-state Briggs-Haldane kinetics assuming that the template: primer binds to the enzyme first, followed by the binding of the dNTP and that the polymerase is a processive enzyme. Based on these assumptions, a velocity equation was derived which allows the calculation of all the specific forward and backward rate constants for the reactions occurring between the enzyme, its substrates and the inhibitor. The calculated rate constants are in agreement with this model and the results indicated that U-9843 acts as a noncompetitive inhibitor with respect to both the template:primer and dNTP binding sites. Hence, U-9843 exhibits the same binding affinity for the free enzyme as for the enzyme-substrate complexes and must inhibit the RT polymerase by interacting with a site distinct from the substrate binding sites. Thus, U-9843 appears to impair an event occurring after the formation of the enzyme-substrate complexes, which involves either an event leading up to the formation of the phosphoester bond, the formation of the ester bond itself or translocation of the enzyme relative to its template:primer following the formation of the ester bond.

Binding Sites↗
PubMed1994

Effect of terbinafine on the pharmacokinetics of cyclosporin in humans.

Cyclosporin is largely metabolized by hepatic cytochrome P450 enzymes, and azole drugs that inhibit cytochrome P450 may precipitate cyclosporin toxicity. The allylamine terbinafine binds to a small subfraction of hepatic cytochrome P450 in type I fashion, and has no effect upon hepatic metabolism of cyclosporin in vitro. The purpose of this study was to determine whether oral terbinafine alters the pharmacokinetics of oral cyclosporin in vivo. Twenty male volunteers (age 19-44 years), were randomly allocated to two groups. The first group received three single oral doses of cyclosporin 300 mg at intervals of 21 d. The second and third doses of cyclosporin were preceded by a 6-d course of oral terbinafine 250 mg each morning. A further 250 mg of terbinafine was taken with the second and third doses of cyclosporin. Blood levels of cyclosporin and terbinafine were monitored for 36 h after each dose. The second group received a 7-d course of terbinafine 250 mg each morning. On the seventh day a single dose of cyclosporin 300 mg was taken together with the terbinafine. Blood levels of both cyclosporin and terbinafine were monitored for 36 h. Two further single doses of cyclosporin 300 mg were given at intervals of 2 weeks and the cyclosporin levels again monitored. In both groups each cyclosporin dose was preceded by an 8-h fast. The mean peak blood concentration of cyclosporin when taken alone was 958 micrograms/l, and 822 when taken with terbinafine. The mean area under the curve for cyclosporin was 4207 micrograms/l/h when taken alone and 3665 when taken with terbinafine. The mean absorption half-life for cyclosporin when taken alone was 0.29 h, and 0.33 when taken with terbinafine. The mean time of maximum concentration and elimination half-life of cyclosporin were unaltered by terbinafine. The results suggest that terbinafine is likely to prove a safe systemic anti-fungal treatment for patients who are taking cyclosporin.

Absorption↗
PubMed1993

Kinetic studies with the non-nucleoside HIV-1 reverse transcriptase inhibitor U-88204E.

The bis(heteroaryl)piperazine U-88204E is a potent inhibitor of HIV-1 reverse transcriptase (RT) and possesses excellent anti-HIV activity in HIV-1-infected lymphocytes grown in tissue culture. Enzymatic kinetic studies of the RNA- and DNA-dependent DNA polymerases of RT were carried out in order to determine whether the inhibitor interacts directly with the template:primer or deoxyribonucleotide triphosphate (dNTP) binding sites of the polymerase. The experimental results were analyzed using steady-state or Briggs-Haldane kinetics, by assuming that the template:primer binds to the enzyme first followed by the dNTP and that the polymerase functions processively. The results of the analysis show that the inhibitor acts as a mixed to noncompetitive inhibitor with respect to both the template:primer and the dNTP binding sites. The potency of U-88204E on the RNA-directed DNA polymerase activity depends on the base composition of the template:primer. The Ki values for the poly(rC):(dG)10-directed reactions were at least 7 times lower than the ones for reactions directed by poly(rA):(dT)10. The inhibitor did not inhibit the RNase H function of HIV-1 RT nor did it impair the RNA-directed DNA polymerase activity of HIV-2 RT. These data thus demonstrate the unique specificity of U-88204E for HIV-1 RT.

HIV Reverse Transcriptase↗
PubMed1993

Inhibition of the tetracycline efflux antiport protein by 13-thio-substituted 5-hydroxy-6-deoxytetracyclines.

A series of 13-(alkylthio) and 13-(arylthio) derivatives of 5-hydroxy-6-deoxytetracycline (tetracycline, Tc) were synthesized and compared to the clinically used antibiotics tetracycline, methacycline, and minocycline for their ability to inhibit tetracycline efflux in an everted membrane vesicle assay of bacterial resistance to tetracyclines. The assay screened for the ability of tetracycline analogues to inhibit [3H]tetracycline uptake into everted membrane vesicles, thereby evaluating the molecular prerequisites for inhibition of an efflux-dependent resistant bacterial system. Thiol adducts attached at the exocyclic C13 carbon of methacycline led to an increase in inhibitor potency as compared to the reference antibiotics. The most potent inhibitors of [3H]tetracycline uptake into everted vesicles among these analogues, particularly members of the alkyl series, revealed important structure-activity relationships between inhibitor potency, steric parameters, and lipophilicity at the C13 sulfur position.

Bacterial Proteins↗
PubMed1992

Mechanism of pHi regulation by locust neurones in isolated ganglia: a microelectrode study.

1. We have measured membrane potential (Em) and intracellular pH (pHi), and sodium and chloride activities (aNai and aCli) in exposed dorsal unpaired median neurones in isolated metathoracic ganglia from the desert locust, Schistocerca gregaria using eccentric double-barrelled ion-sensitive microelectrodes. 2. In the absence of added HCO3- the steady-state pHi was 7.21 +/- 0.13 (mean +/- S.D.) at a mean membrane potential of -37 +/- 7.0 mV (S.D.) (n = 44 cells). The pHi was always more alkaline than predicted for passive H+ distribution. 3. The pHi recovery from acid loads, induced by weak acid application or weak base removal, was pHi dependent and associated, in both the presence and absence of added CO2-HCO3-, with a transient increase in aNai. 4. In the absence of added HCO3-, application of the Na(+)-H+ exchange blocker amiloride or external Na+ removal caused intracellular acidification. Also in the absence of added HCO3- the inhibitor SITS (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid) caused an acidification of about 0.2 pH units which was not additive to the effects of the removal of external Na+. 5. We found that the application of a CO2-HCO3(-)-containing solution increased the rate of pHi recovery from acidification. 6. Intracellular chloride was decreased by intracellular acidification in the presence of added CO2-HCO3-. In the presence of amiloride, intracellular Cl- depletion inhibited pHi regulation. 7. Simultaneous application of SITS (160 microM) and removal of CO2-HCO3- revealed a continuous underlying acid load of 0.03-0.05 pH unit min-1. 8. We conclude that locust neurones possess at least two pHi-regulating mechanisms which operate against a continuous acid load. One is a Na(+)-H+ exchanger which can be blocked by amiloride, while the second is a Na(+)-dependent Cl(-)-HCO3- exchanger. The latter mechanism appears to be able to operate in the absence of added HCO3- and can recover pHi to around pH 7.4; it is probably the main pHi regulating mechanism. The Na(+)-H+ exchanger appears to activate at more acid pHi and being less energy efficient may serve a protective role.

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