PubMed Health⌕ Search

Biomedical subjects

B Allard

Publications and source records attributed to B Allard.

33 records · Page 2Linked to original sources
PubMed1994

The effects of chloride ions in excitation-contraction coupling and sarcoplasmic reticulum calcium release in twitch muscle fibre.

Using the sucrose vaseline gap technique, experiments were carried out on isolated frog twitch muscle fibre to investigate the role of chloride ions in excitation-contraction coupling. In current clamp conditions, replacement of chloride ions by impermeant anions led to an increase of the amplitude of the early after potential and of the amplitude of the twitch. Addition of a chloride channel blocker, anthracene-9-carboxylic acid gave similar results. In voltage clamp conditions, replacement of chloride ions by impermeant anions induced a decrease of the outward current and an increase of both the amplitude of the contraction and of the resting tension. Addition of anthracene-9-carboxylic acid gave similar results except that resting tension was not modified. Replacement of chloride ions by impermeant anions resulted in a shift of the tension-voltage relationship toward negative potentials and in an increase of the amplitude of the contraction at all potentials. Outward currents were also reduced at all potentials but no shift of the current-voltage relationship was observed. Similar results were obtained upon addition of anthracene-9-carboxylic acid. Rapid filtration experiments were performed on isolated sarcoplasmic reticulum vesicles to study the role of chloride ions in Ca2+ release. Under conditions where KCl was present in the intra- and extravesicular media, removal of chloride ions from the release solution produced a 2-fold increase in the rate of Ca(2+)-induced Ca2+ release. Together, these results suggest that, besides their involvement in the action potential time course, chloride ions could exert a negative control on the sarcoplasmic reticulum Ca2+ release.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1993

Pharmacological properties of ATP-sensitive K+ channels in mammalian skeletal muscle cells.

The patch-clamp technique (single-channel recordings) was used to study the effects of glibenclamide and some channel openers on the KATP channel in mouse skeletal muscle. In outside/out membrane patches, glibenclamide reversibly inhibited KATP channel activity in a dose-dependent manner with an apparent Ki of 190 nM. In inside/out membrane patches, RP 61419 increased KATP channel activity both in the absence and in the presence of internal ATP while other K+ channel openers such as nicorandil and cromakalim required the presence of internal ATP to evoke channel activation. The half-maximal activity effect for cromakalim, with 0.5 mM ATP at the cytoplasmic face, was observed at about 220 microM. Pinacidil was unable to activate the KATP channel in the absence of internal ATP and could even reduce channel opening in situations where activity was high in the control. In the presence of internal Mg2+, activation by pinacidil occurred when ATP or low and weakly activating concentrations of ADP were present at the cytoplasmic side. Pinacidil activation could also be observed in the presence of ATP or ADP when Mg2+ was absent from the internal solution. The mechanism of action of pinacidil is discussed in terms of interactions between the different nucleotide regulatory sites and the K+ channel opener binding site of the KATP channel. Half-maximum activation of the KATP channel in the presence of 0.5 mM ATP at the cytoplasmic face was observed at 125 microM pinacidil.

Adenosine Triphosphate↗
PubMed1993

Inward barium current and excitation-contraction coupling in frog twitch muscle fibres.

The role of barium ions in excitation-contraction coupling was studied in single isolated frog semitendinosus fibres. Simultaneous recordings of membrane currents and contraction under voltage-clamp conditions in a sucrose-vaseline gap device show that barium ions have a reversible inhibiting effect on contraction. This inhibiting action was correlated to the entry of barium ions via the DHP-sensitive tubular calcium channel. Cytological observations and X-ray microanalysis performed on the fibres used in the electrophysiological experiments indicate that barium ions do not accumulate in the junctional sarcoplasmic reticulum; they can freely diffuse in the intermyofibrillar space and they accumulate in mitochondria. Calcium release experiments performed on isolated sarcoplasmic reticulum vesicles show that barium ions are not able to induce calcium release from calcium-loaded vesicles, they behave as calcium release inhibitors. These results are discussed in relation with the possible role of the slow Ca current in excitation-contraction coupling.

Animals↗
PubMed1993

Influence of growth status on composition of extra-cellular polysaccharides from two Chlamydomonas species.

The extracellular polysaccharides released by Chlamydomonas augustae at the beginning of growth contain mainly arabinose, glucose and galactose. Methylation analysis revealed that the major fraction of these extracellular polysaccharides can be described as a highly branched polymer composed of (1, 3, 4)-linked glucose and terminal arabinose and galactose units. The chemical composition of these extracellular polysaccharides varies during growth and in the stationary phase of growth glucose and glucuronic acid are the main components. The major fraction of the extracellular polysaccharides can be then described as a linear polymer composed of (1, 4)-linked glucose and (1, 4)-linked glucuronic acid. In sharp contrast, the extracellular polysaccharides from C. corrosa are independent of growth status and contain arabinose and galactose as major sugars. Methylation analysis indicated a highly branched polysaccharide composed of arabinose as unique branch point units and of terminal galactose residues.

Amino Acids↗
PubMed1993

Microspectrofluorometry of the protonation state of ellipticine, an antitumor alkaloid, in single cells.

The protonation state and intracellular distribution of ellipticine were investigated in single human mammary T47D cells by confocal laser microspectrofluorimetry. In the cell nucleus, only the protonated form of ellipticine was detected as a direct consequence of its apparent pK increase upon DNA binding. Both protonated and neutral forms were present in the aqueous cytoplasm, where the pH is close to the drug pK. When cells were incubated in high concentrations of K+, a condition that depolarizes the plasma membrane potential, ellipticine cellular accumulation was reduced. In the cytoplasm, ellipticine was mainly bound to mitochondria, and its protonation equilibrium was shifted toward the neutral form. The fluorescence spectrum of ellipticine bound to mitochondria was insensitive to valinomycin, whereas it was markedly shifted toward the protonated form after carbonyl cyanide p-trifluoromethoxy-phenylhydrazone or nigericin addition. Similar studies with ellipticine bound to isolated mitochondria suggest that it behaves as a fluorescent probe of mitochondrial pH in both isolated mitochondria and single living cells.

Biophysical Phenomena↗
PubMed1992

BisG10, a K+ channel blocker, affects the calcium release channel from skeletal muscle sarcoplasmic reticulum.

The action of bisG10, a potent K+ channel inhibitor, was tested on the Ca2+ release from isolated sarcoplasmic reticulum vesicles of rabbit skeletal muscle. Using a rapid filtration technique, we found that the drug inhibited Ca(2+)-induced Ca2+ release elicited in the presence of extravesicular K+ as counter-ion. This inhibition was not reversed by the addition of valinomycin and still occurred when Cl- was used as co-ion, indicating that not only K+ channels are involved in the inhibiting effect. We found that bisG10 decreased the binding of ryanodine to sarcoplasmic reticulum vesicles, showing that bisG10 is able to block the sarcoplasmic reticulum Ca2+ release channel.

Animals↗
PubMed1992

Determination of the carboxyl content in humic substances by methylation.

The carboxyl content of different fulvic acids was estimated by means of a methylation technique. The procedure involved methylation by diazomethane followed by base catalyzed hydrolysis, esterification with propionyl chloride and gas chromatographic analysis of the methyl ester formed. After optimization of each step, the whole sequence of reactions was performed using only a few milligrams of starting material. The method was applied to two fulvic acid samples of different origin (surface water and groundwater, respectively). The carboxylic content was estimated to about 3.5 meq/g material for the surface water fulvic acid and about 4.5 meq/g material for the groundwater fulvic acid. This estimates approximately 80% of the total content of acidic groups obtained for the same materials by using potentiometric titration.

Benzopyrans↗
PubMed1992

Nucleotide diphosphates activate the ATP-sensitive potassium channel in mouse skeletal muscle.

Patch-clamp techniques were used to study the effects of internal nucleotide diphosphates on the KATP channel in mouse skeletal muscle. In inside-out patches, application of GDP (100 microM) and ADP (100 microM) reversibly increased the channel activity. In the presence of internal Mg2+ (1 mM), low concentrations of ADP (< 300 microM) enhanced channel activity and high concentrations of ADP (> 300 microM) limited channel opening while GDP activated the channel at all concentrations tested. In the absence of internal Mg2+, ADP decreased channel activity at all concentrations tested while GDP had no noticeable effect at submillimolar concentrations and inhibited channel activity at millimolar concentrations. GDP [beta S] (100 microM), which behaved as a weak GDP agonist in the presence of Mg2+, stimulated ADP-evoked activation whereas it inhibited GDP-evoked activation. The K+ channel opener pinacidil was found to activate the KATP channel but only in the presence of internal GDP, ADP and GDP [beta S]. The results are discussed in terms of the existence of multiple nucleotide binding sites, in charge of the regulation of the KATP channel.

Adenosine Diphosphate↗
PubMed1992

Reappraisal of the role of sodium ions in excitation-contraction coupling in frog twitch muscle.

Tetanic and twitch tension were recorded on isolated frog twitch fibres under experimental conditions modifying the influx of sodium ions. In current clamp conditions replacing Li+ for Na+ did not modify the electrical activity but drastically decreased the plateau of tetanic tension. In voltage clamp conditions replacing Li+ for Na+ did not modify the inward currents but induced a marked decrease of the plateau of the tetanic tension for depolarizations between the activation threshold and the reversal potential of sodium current. Under veratridine treatment, during tetanic depolarization, a slow inward sodium (or lithium) current developed. This induced a parallel increase of the tetanic tension which was much more pronounced in sodium than in lithium containing solution. The twitch tension obtained during short depolarization was increased by greater than 100% during veratridine treatment with a sizeable decrease (40%) of the delay between the end of depolarization and the beginning of tension. All these results could be reproduced in calcium-free solution. Our data confirm that the entry of sodium ions (and to a lesser extent of lithium ions) is able to modulate the release of calcium from the sarcoplasmic reticulum (SR). We discuss these results in terms of a model where sodium ions entering the compartment between the tubular membrane and the SR junctional membrane carry counter charges through the SR K+ channels and help to maintain the SR Ca2+ release. This could occur in particular during a physiological tetanic contraction where the junctional compartment is probably filled with Na+ ions and depleted of K+ ions.

Action Potentials↗
PubMed1991

Action of heptaminol hydrochloride on contractile properties in frog isolated twitch muscle fibre.

1. Heptaminol stopped or delayed the progressive decline in tension which characterizes the phenomenon of fatigue in frog isolated twitch muscle fibre. 2. Heptaminol had no action on the sodium, potassium and calcium voltage-dependent ionic conductances. 3. The hypothesis of an action via an internal alkalinization was tested by comparison with the action of NH4Cl. Both substances increased the tension. 4. The action of heptaminol was suppressed in sodium-free (TRIS) solution or in the presence of amiloride while the action of NH4Cl was always observed. 5. These results could be explained by a stimulation of the Na/H antiport by heptaminol.

Action Potentials↗
PubMed1991

Audiology in medicine.

Among the most common complaints a physician confronts are those concerned with hearing loss and dizziness. It is essential that all practitioners acquaint themselves with the diagnostic information provided by an audiological evaluation. The authors describe the frequently used tests and present case studies to illustrate the value and scope of diagnostic audiology.

Adult↗
PubMed1990

Diagnostic value of vertical nystagmus recorded from ENG.

A patient with a cerebellar hemorrhage was evaluated using electronystagmography (ENG). Data obtained on the horizontal channel were only mildly abnormal. However, vertical nystagmus was clearly evident when the patient was tested in a darkened room with eyes open. This additional procedure may have saved the patient severe complications. With eyes open in darkness vertical nystagmus is more easily differentiated from eye blinks and clinicians are encouraged to look for this valuable central vestibular system sign.

Adult↗
PubMed1988

Effects of Glucose Concentrations on Cadmium, Copper, Mercury, and Zinc Toxicity to a Klebsiella sp.

The influence of glucose concentration on Cd, Cu, Hg, and Zn toxicity to a Klebsiella sp. was studied by following the degradation of C-labeled glucose at pH 6.0. Uptake of C into the cells was also determined. The carbon concentrations ranged from 0.01 to 40 mg liter, which are equivalent to soluble C concentrations in natural environments. The toxicity of Cu, Cd, and Zn to a Klebsiella sp. was affected considerably by the C concentration. Copper at 10 M was toxic when the carbon concentration was 10 or 40 mg liter, while at 0.01 to 1.0 mg liter no toxicity was observed. Cadmium and zinc were toxic at 10 M in media containing 0.01 to 1.0 mg of C liter. At C concentrations greater than 1.0 mg liter, the inhibition of glucose degradation and carbon assimilation was observed at 10 M Cd and Zn. The toxicity of mercury seemed to be independent of the C concentration. Results of this study showed that the nutritional state of an organism may have a profound effect on its sensitivity to metals. Metals taken up by an energy-driven transport system may be less toxic under conditions of C starvation. The C concentration should be taken into account when evaluating results from toxicity studies, especially as most microorganisms in nature live under energy-limited conditions.

Journal Article↗
PubMed1985

Lipid peroxidation and alpha-tocopherol during an acute respiratory failure after near drowning.

We compare two patients admitted after near drowning. Both presented a severe metabolic acidosis, but only one of them developed an acute pulmonary edema with hypoxemia. An increase of lipid peroxides associated with a reduction of vitamin E concentration has been observed in this later patient. Lipid peroxidation, one of the important causes of disruption of cellular membranes after some injuries, could be implicated in the pathogenesis of lung edema in this patient.

Acute Disease↗