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Biomedical subjects

A Crevat

Publications and source records attributed to A Crevat.

At least 37 records · Page 2Linked to original sources
PubMed1993

Chloride dependent intracellular pH increase induced by bepridil in human red blood cells: a possible involvement in correction of ischemic acidosis.

Inhibitors of Na+/H+ exchanger are reported to exert an anti-ischemic effect. Some calcium antagonists and particularly bepridil are commonly used as anti-ischemic agents. Therefore, in this study, we test the hypothesis that protective effect against ischemia may occur at least in part through an action on Na+/H+ exchanger. The effect of some calcium antagonists on Na+/H+ exchanger from acid-loaded and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid disodium salt (DIDS)-treated human red cells (RBC) has been studied with a pHstat technique. Doses above those required to affect calcium channel (10(-5) and 10(-4) M) of nifedipine, nicardipine, verapamil and diltiazem had no effect on Na+/H+ exchanger activity. Ethyl isoproply amiloride (10(-4) M) completely inhibited the exchanger. Among the calcium antagonists tested, bepridil exhibited a particular effect, dissipating the pH gradient independently from the Na+/H+ exchanger activity. Bepridil's effect on DIDS-treated RBC was compared with that of a well known protonophore, carbamyl cyanide p-(trifluoromethoxy)phenyl hydrazone, and with that of tributyltin, which mediates a Cl-/OH- exchange across the cell membrane. Bepridil (> 2 x 10(-6) M) acts like tributyltin by dissipating the pH gradient whatever the external cation (Na+ or K+) or the membrane potential, and its action depends on the ratio intracellular [Cl-]/extracellular [Cl-]. The dissipation seems to occur through an OH-/Cl- exchange but other mechanisms may intervene. Moreover, intraerythrocytic pH measurement by 31P nuclear magnetic resonance clearly showed that bepridil permits the cell to recover normal pH faster than control.(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1993

2,3 diphosphoglycerate-haemoglobin binding in uraemic patients treated with erythropoietin. A 31P-nuclear magnetic resonance study.

Using 31P-nuclear magnetic resonance (NMR) measurements of relaxation rate for 2,3 diphosphoglycerate (DPG) phosphorus atoms, we showed previously that in uraemic red blood cells the DPG-haemoglobin binding is stronger, thus stabilizing the deoxyhaemoglobin form and hence facilitating oxygen release. Here we verified if these modifications of spatial environment of DPG remain in uraemic patients treated by human recombinant erythropoietin (rHuEpo). Simultaneously we measured the intraerythrocytic ATP concentration (ATPi) and pH (pHi) of patients. Our results show a slight decrease on pHi and ATPi values during rHuEpo treatment. For the DPG relaxation rates, we observed a very weak but statistically significant increase 6 months after the beginning of treatment, but we cannot attribute a physiopathological significance to these results because of the lack of accuracy of the NMR determination of relaxation rate in red blood cells. Therefore, the DPG-haemoglobin binding is always stronger than in normal subjects.

2,3-Diphosphoglycerate↗
PubMed1993

In vivo accumulation of sodium pump inhibitor by normal and uremic erythrocytes.

A uremic toxin fraction (fraction 2-3-1) in the middle molecular mass range (300-2000 Da) containing a sodium potassium inhibitor pump was studied. As fraction 2-3-1 was known to be present in minute quantities in urine and plasma, erythrocyte lysates were used as an alternative source. Results show that fraction 2-3-1 is more abundant in erythrocytes than in normal urine. In addition, the fraction is present in a greater quantity in uremic erythrocytes than in normal blood cells. It is concluded that fraction 2-3-1 is concentrated at the erythrocyte level in uremic patients.

Chromatography, Gel↗
PubMed1992

Inhibition of sodium pump by bepridil. An in vitro and microcalorimetric study.

The effects of diltiazem, verapamil, bepridil, nicardipine and nifedipine were studied in vitro on Na+,K(+)-ATPase from dog kidney (EC 3.6.1.37). Except diltiazem, all the drugs tested showed an inhibitory effect on Na+,K(+)-ATPase activity in a dose-dependent manner. Among these drugs bepridil is far more effective than the others (IC50 approximately 10(-4) M). Competition studies showed that bepridil acted in a non-competitive manner with the ATP-Mg2+ complex and in a partially competitive manner with K+. Since ouabain acted similarly under the same experimental conditions, we tested the interaction of bepridil and ouabain on Na+,K(+)-ATPase. With low doses of ouabain, the enzyme inhibition corresponded to a potentiated synergy of the two drugs. We then studied the action of bepridil on the sodium pump activity of intact red blood cells by an ex vivo microcalorimetric technique. At 10(-5) M bepridil caused a significant decrease in sodium pump activity (33 +/- 8%).

Adenosine Triphosphate↗
PubMed1992

A double-blind placebo-controlled trial of L-threonine in amyotrophic lateral sclerosis.

Fifteen patients with the unequivocal diagnosis of amyotrophic lateral sclerosis (ALS) completed a 1-year randomized double-blind placebo-controlled trial of L-threonine (2 g daily). During the study, patients in the placebo group showed a decline in functional status consistent with the natural history of ALS, which was not statistically different from outcome in the patients in the L-threonine group.

Aged↗
PubMed1992

The restoration of ATP synthesis may explain the protective effect of calcium antagonists against cyclosporine A nephrotoxicity.

Cyclosporine A at pharmacological doses decreases the rate and yield of ATP synthesis in rat mitochondria. This action seems to be due to the mitochondrial calcium storage induced by the drug. If such an effect occurs in vivo, the ATP deficit will affect calcium extrusion pumps, so triggering vasoconstriction which is the major side effect of Cyclosporine A. Calcium antagonists (Nifedipine and Verapamil) at least partially correct this effect on ATP synthesis: this finding may be related with the beneficial clinical effect conferred on Cyclosporine A toxicity by calcium antagonists. This effect of calcium antagonists may be due to an interaction with Cyclosporine A at the level of mitochondrial calcium efflux.

Adenosine Triphosphate↗
PubMed1992

Sodium pump activity in uremic erythrocytes: a microcalorimetric study.

Erythrocyte thermogenesis was studied by flow microcalorimetry in 25 healthy subjects and 27 uremic patients. The heat production (HP) from cells in plasma, decrease in HP induced by ouabain (a specific sodium pump inhibitor) and index of rate response to ouabain action were measured. HP was higher in uremic patients than controls. Sodium pump inhibition with ouabain induced the same decrease in HP in the two groups. The index of rate response to ouabain action was lower in uremic patients than in controls. The difference in total HP may be due to a different age distribution of erythrocytes. Mean sodium pump activity was identical in the two groups, but some patients had lower activity than controls. Ouabain seems to act more slowly in many patients than in controls, perhaps because of hindered binding of the inhibitor.

Calorimetry↗
PubMed1991

Qualitative study of the interaction mechanism of estrogenic drugs with tubulin.

Synthetic estrogenic drugs (E-diethylstilbestrol, erythro-hexestrol and E,E-dienestrol) inhibit tubulin assembly and erythro-hexestrol and E,E-dienestrol lead to the formation of twisted ribbon structures. For the inhibitory effect on tubulin assembly, estrogenic drugs seem to interact directly with tubulin 6S on site(s) analogous to the colchicine-site, but independent of the GTP- and vinblastine-sites. This binding does not involve tubulin tryptophanyl residues or sulfhydryl groups. The influence of temperature, calcium and magnesium on the formation of twisted ribbon structures induced by the binding of estrogenic drugs to microtubular protein and tubulin has also been studied. This formation is strongly magnesium-dependent whereas preformed twisted ribbon structures are calcium- and chilling-insensitive.

Binding Sites↗
PubMed1991

Counteraction by nicardipine of the ionophoretic effect of gliclazide: a mitochondrial study.

Using mitochondria, we demonstrate that gliclazide exhibits a calcium ionophoretic activity. Indeed, gliclazide induces a decrease in the respiratory control of mitochondria; this effect is increased by addition of Ca2+ and corrected by ruthenium red, all characteristics of a calcium ionophoretic compound. Our results, on a biological membrane, confirm previous findings in vitro. Moreover, we show that nicardipine counteracts the action of gliclazide. Besides the effect on ATP-stimulated K+ channels, the ionophoretic effect of gliclazide may play a role in its hypoglycaemic effect, thus this counteracting action of nicardipine might induce drug interaction during the concomitant clinical administration of gliclazide and nicardipine.

Animals↗
PubMed1991

1H nuclear magnetic resonance and clinical studies of interaction of calcium antagonists and hypoglycemic sulfonylureas.

The hypoglycemic effect of gliclazide is mainly due to its action on ATP stimulated K+ channels, but the calcium ionophoretic effect of this drug may also be involved in its physiological properties. Using 1H NMR we demonstrated the antiionophoretic effect of nifedipine and diltiazem. We attempted to verify whether this in vitro interaction also occurs in vivo. A clinical trial, was performed on patients treated concomitantly with gliclazide and nifedipine or diltiazem. Results showed that no in vivo interaction occurred. The discrepancy between in vivo and in vitro results may be explained by a too weak plasma concentration in the case of nifedipine and by a large plasma protein binding in the case of diltiazem.

Adenosine Triphosphate↗
PubMed1991

Restoration by biotin of the in vitro microtubule formation inhibited by uremic toxins.

Tubulin is an intracellular protein whose in vivo polymerization leads to the formation of microtubules (MT). MT are essential component of axons of nerve cells. This reaction is the limiting factor in the growth of axons. Uremic neuropathy is characterized in part by an axonal degeneration. A chromatographic fraction from uremic plasma (2-5 fraction) inhibits in vitro the tubulin polymerization and thus MT formation and therefore may be implicated in the occurrence of uremic neuropathy. In vitro, biotin counteracts the inhibitory effect of 2-5 fraction on MT formation. This effect could be a partial explanation of the possible clinical improvement brought on by biotin in uremic neuropathy.

Biopolymers↗
PubMed1991

[Anomaly in the neurotransmitter amino acids in amyotrophic lateral sclerosis: a therapeutic application].

Although the cause of amyotrophic lateral sclerosis remains unknown, the excitatory amino acids may be involved in its pathogenesis. Glutamate level analysis shows a differential distribution of the amino acids. One of the therapeutic methods consists of reinforcing the inhibitory amino acid activity using L-threonine which has been shown to improve some symptoms and signs of ALS.

Adult↗
PubMed1990

Kinetic modeling of intracellular pH and comparison with 31P NMR experimental values in dialysed uremic patients.

Changes in intra-erythrocytic pH values over time, during and after bicarbonate hemodialysis, were studied with 31P Nuclear Magnetic Resonance. Simultaneously, pH values of whole blood were obtained by a gazometric method. A two-compartment model appeared to be the simplest kinetic model to explain the shifts in proton concentrations in extra- and intra-cellular media. Non-linear regression was used to determine exchange constant values. There was a very good correlation between the experimental and calculated proton concentrations. This model can describe all patients but individual experimental constants must be determined. Under these conditions a single blood pH determination before dialysis will permit determination of the initial intra-erythrocytic pH and monitoring of intra-erythrocytic pH during hemodialysis.

Acid-Base Equilibrium↗
PubMed1989

Intraerythrocytic water relaxation rates in amyotrophic lateral sclerosis. An NMR investigation.

Water relaxation rates 1/T2 in erythrocytes from amyotrophic lateral sclerosis (ALS) patients were studied by NMR. The spin-spin relaxation time of water protons in erythrocyte suspension was measured in the presence of a paramagnetic reagent which did not enter the cell. Our results show that red blood cell membranes exhibit a diminished water permeability in some ALS patients. Moreover, the activation energy value of water is lower in ALS patients than in healthy controls.

Adult↗
PubMed1989

Phosphorus-31 and water proton relaxation in living erythrocytes. Application to uremia.

We measured the spin-lattice and spin-spin relaxation times (T1 and T2, respectively) and the nuclear Overhauser effect (NOE) of 31P nuclei of 2,3-diphosphoglycerate (2,3-DPG) in living erythrocytes. The relaxation of water protons was also studied. Phosphorus relaxation is pH-dependent due to a modification of the binding of 2,3-DPG to hemoglobin. We compared the results obtained with normal and uremic erythrocytes. In uremic erythrocytes the 31P relaxation rates are increased, but the intraerythrocytic pH variation in uremic erythrocytes cannot itself explain this increase. A possible role of dialysable substances may explain the increased relaxation rate.

2,3-Diphosphoglycerate↗
PubMed1989

Intraerythrocytic pH variations during hemodialysis: a 31P NMR study.

Before hemodialysis, patients have an intraerythrocytic pH (pHi) and an extracellular pH, measured in whole blood (pHo), which are lower than those of healthy controls. During bicarbonate hemodialysis, pHi values continuously increase, approaching a normal value at the end of the session. Concomitantly, pHo values follow similar variations. During acetate hemodialysis, pHi values exhibit a steep initial decrease, reaching a minimum after about 15 minutes. Concurrently, however, pHo values decrease only slightly. This phenomenon seems to originate in the intraerythrocytic medium and might be due to a shift in intracellular CO2/bicarbonate equilibrium. This drop in pHi exhibits interpatient variability, suggesting that the magnitude of pH decrease would be correlated with the degree of the problems observed in some patients undergoing acetate hemodialysis.

Acetates↗
PubMed1988

23Na nuclear magnetic resonance study of Na+-K+ pump inhibition by a fraction from uremic toxins.

An in vitro inhibitor of Na+/K+-transporting ATPase (EC 3.6.1.37) was isolated from uremic plasma and normal urine by liquid chromatography. A 23Na nuclear magnetic resonance study involving living erythrocytes showed that this inhibitor causes impairment of the Na+-K+ pump of intact erythrocytes. This finding may explain the high intra-erythrocytic sodium concentration in those uremic patients exhibiting a high concentration of this inhibitor. The presence of this same inhibitor in normal urine suggests that it may play a physiological role.

Animals↗