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Biomedical subjects

Y Mounier

Publications and source records attributed to Y Mounier.

At least 55 records · Page 3Linked to original sources
PubMed1990

Contractile properties of rat soleus muscle after 15 days of hindlimb suspension.

The properties of the contractile elements interacting to develop force in atrophied rat soleus muscle were studied by using single skinned fibers, which permitted direct access to the contractile apparatus. Muscle atrophy was induced by 15 days of hindlimb suspension. Suspension resulted in a decrease of maximal tension relative to an important decline in fiber diameter. Ca affinity of the contractile proteins was not changed insofar as the tension-pCa relationship was not shifted along the pCa axis. However, after hindlimb suspension 1) the value of the Hill coefficient from the tension-pCa curve was found to be higher, 2) a higher Ca threshold for activation was reported, and 3) a significant increase in contraction kinetics was described. All these results suggested that after suspension the mechanical properties of the slow-twitch soleus appeared to resemble more closely those of a fast-twitch muscle. Our results were in complete agreement with published histochemical data.

Animals↗
PubMed1989

Compared properties of the contractile system of skinned slow and fast rat muscle fibres.

Chemically skinned fibres from soleus and plantaris rat muscles were used to compare the contractile properties of slow and fast muscles. The maximal isometric tension appeared larger in plantaris than in soleus fibres. The apparent Ca2+ threshold for activation was lower in slow than in fast fibres while Ca2+ concentrations required to obtain either the maximal tension or half maximal tension (pCa50) were lower in fast than in slow fibres. This apparent difference in Ca2+ sensitivity will be discussed. As could be expected from other studies, a faster force development in plantaris than in soleus fibres occurred. However, one interesting new result showed that in soleus, the kinetics of the tension development estimated by the tmax parameters were slightly dependent on the Ca2+ concentration whereas the t50 parameter changed significantly with the Ca2+ concentration. In plantaris, both tmax and t50 parameters were found to depend strongly on the Ca2+ concentration. Finally, the plantaris muscle showed a greater caffeine sensitivity than the soleus muscle. All the results suggested that the Ca-regulatory mechanism in the slow fibres was essentially different from that in the fast fibres.

Animals↗
PubMed1988

Calcium-induced and voltage-dependent inactivation of calcium channels in crab muscle fibres.

Inactivation of Ca channels was examined in crab muscle fibres using the voltage-clamp method. A satisfactory suppression of outward currents was attempted by the use of K+ blocking agents: TEA, 4AP and Cs ions instead of K+ ions applied extracellularly. The inactivation of Ca current appeared as a bi-exponential process. The faster component had a mean value of the time constant of 50 ms while the second component inactivated at a tenfold slower rate. The extent of inactivation of the faster component increased as the Ca current itself increased in different experimental conditions. Inactivation decreased when ICa was reduced for large applied depolarizations. The time constant of the faster calcium component also depended on the calcium current. Thus the results suggested that Ca2+ entry leads to inactivation of one component of calcium current in crab muscle. Substitution of Ca2+ ions by Sr2+ or Ba2+ ruled out the hypothesis concerning an accumulation process which would explain the decrease of the inward current. The second slower component of Ca current was better described by a voltage-dependent mechanism and its rate was not modified in Ca2+ rich solution or when the inward current was carried by Sr2+ or Ba2+ ions. Thus in crab muscle fibres, inactivation is mediated by both calcium entry and a voltage-gated mechanism.

Animals↗
PubMed1987

Activation of skinned muscle fibers by calcium and strontium ions.

Intact and mechanically skinned skeletal muscle fibers of the crab Carcinus maenas have been used. The aim of the experiments was to determine the origin of the mechanical activity recorded in intact crab muscle fibers exhibiting an inward strontium current in strontium solution without calcium. To do so, the effect of strontium ions in inducing activation of contractile proteins and calcium release from the sarcoplasmic reticulum has been studied. The properties of the sarcoplasmic reticulum membrane towards strontium ions, i.e., the efficiency of the calcium ATPase towards strontium ions and the capability to release strontium ions have been investigated. Results show that the contractile proteins have a lower affinity for strontium than for calcium ions. However, the maximum bound strontium is identical to the maximum bound calcium. As for the sarcoplasmic reticulum, strontium ions can induce a calcium release and also can be taken up by the calcium ATPase and be released. We concluded that the mechanical activity in intact fibers bathed in a strontium medium has two origins: first, a direct and partial activation of the contractile proteins by strontium ions flowing through the calcium channel; second, a contractile proteins activation of calcium ions released by the sarcoplasmic reticulum by a "strontium-induced calcium release" mechanism.

Animals↗
PubMed1987

Role of the different calcium sources in the excitation-contraction coupling in crab muscle fibers.

Excitation-contraction coupling in crab muscle fibers was studied in voltage-clamp conditions. Extracellular calcium is essential for the mechanical activity. Two calcium influxes induced by membrane depolarization contribute to tension development: one is the inward calcium current responsible for the phasic tension, the other is a calcium influx dependent on extracellular sodium and calcium concentrations and is responsible for the tonic tension. These calcium influxes are not sufficient to activate contractile proteins. Experiments with procaine and caffeine show that a calcium release from the sarcoplasmic reticulum is required.

Animals↗
PubMed1986

Calcium-induced calcium release mechanism from the sarcoplasmic reticulum in skinned crab muscle fibres.

Mechanically skinned skeletal muscle fibres of the crab Carcinus maenas have been used to investigate the mechanism of calcium release from the sarcoplasmic reticulum. Calcium release has been monitored by the amplitude and kinetics of the tension developed by the fibre. Results show that a very low calcium concentration, insufficient to directly activate contractile proteins, induces a release of calcium from the SR. This release is stimulated by low concentrations of caffeine and inhibited by small amounts of EGTA. Thus, a graded calcium-induced calcium release mechanism dependent on extrareticular calcium concentration has been demonstrated in skinned crab muscle fibre.

Animals↗
PubMed1986

[Behavior of contractile proteins of rat muscle fibers under microgravity conditions].

Microgravity effects were studied on three muscles: gastrocnemius lateralis, plantaris and diaphragm, after the biocosmos 1514 and 1667 space flights. Results showed a decrease of maximal mechanical activity on both gastrocnemius and plantaris while no modification was observed on diaphragm. Cross-bridge cycling speed was reduced on both gastrocnemius and plantaris. Moreover, a reduced calcium binding affinity appeared in gastrocnemius.

Animals↗
PubMed1984

Intramuscular calcium movements: experiments from the Soviet biosatellite Biocosmos.

Experiments have been performed in skeletal muscle fibres from the lateral head of gastrocnemius muscle of female rats. Changes in intramuscular calcium movements due to microgravity conditions have been tested by tension measurements in chemically skinned muscle fibres. Our results show that microgravity induces i) a decrease in maximal muscle strength developed by contractile proteins ii) a decrease of intensity and rate of both Ca release and Ca uptake by the sarcoplasmic reticulum.

Animals↗
PubMed1981

Effects of ryanodine on the ionic currents and the calcium conductance in crab muscle fibers.

The effects of ryanodine, a neutral alkaloid, on crab muscle fibers were investigated under voltage clamp conditions using the double sucrose-gap technique. In the presence of ryanodine, contracture develops without any membrane depolarization and the Ca-conductance variables are shifted in a hyperpolarizing direction. As a result, the Ca channels are activated at the resting potential. During the action potential, the Ca channels appear to open faster and for a longer period of time. The K currents are also modified. These different effects may be interpreted by a common mechanism related to a change of the membrane electrical field induced by increased Ca activity in the cytoplasm.

Action Potentials↗
PubMed1979

Inactivation of the slow potassium outward current in crab muscle fibre.

The slow outward current (IK2) recorded in crab muscle fibre using the double sucrose gap method decreases when high and maintained depolarizations are applied. This decrease corresponds to a true inactivation of the potassium conductance rather than to a shift in the reversal potential of the charge carrying ion following local accumulation.

Animals↗
PubMed1979

Is there a voltage-dependent Cl conductance or do Cl ions modify other conductances in crab muscle fibre?

1. The electrical activity of crab muscle fibre disappeared in Cl-deficient solutions when Cl was substituted by an impermeant anion. 2. Under voltage-clamp conditions, the above solutions abolished Ca-inward current and altered K-outward currents. 3. In 84 mEq-Cl solutions, (Cl substituted by methane sulfonate or proprionate) it is chiefly in gCa-availability that was modified. Half-availability was shifted by 50 to 70 mV in a hyperpolarizing direction while the slope factor was noticeably increased. Similar effects, but of less amplitude, were observed when decreasing the external Cl concentration to 255 mEq. 4. Ca- and slow K-activation variables were shifted by 17 mV and 20 mV respectively in a hyperpolarizing direction by the Cl-poor (84 mEq) solution. Cl-deficiency was even more efficient on the fast outward current than on the Ca current; the former current could be significantly reprimed only if the Cl-concentration was reduced by about 10 per cent. 5. In Cl-deficient solution, electrical activity could be restored by injecting hyperpolarizing currents in order to reprime the Ca-conductance. 6. It is suggested that Cl-ions bind to positive charges on both sides of the membrane. When substituted by impermeant anions, the local anion concentration decreases at the internal surface of the membrane, thus reducing the strength of the effective field of the membrane.

Animals↗
PubMed1975

Initial and delayed membrane currents in crab muscle fibre under voltage-clamp conditions.

Membrane currents are investigated under voltage-clamp conditions in crab muscle fibre. 2. Step depolarizations elicit an initial composite current followed by a late outward current. 3. One of the components of the initial current is inward. It is sensitive to the external calcium concentration and inhibited by manganese ions, it can be carried also by strontium ions; thus it is expected to be a calcium current. 4. In TEA solution this calcium current appears alone, it reverses when the membrane polarization is carried beyond an internal potential of +30 or +35 mV. Such a low equilibrium potential for calcium ions can be explained either by a low selectivity of the calcium channel or by a local accumulation of calcium ions. 5. Calcium conductance shows voltage- and time dependence. 6. The late outward current corresponds to a potassium current and is inhibited by TEA ions. Its activation exhibits voltage- and time dependence. 7. The activation curve of the late potassium current is shifted in a depolarizing direction by addition of manganese ions. A similar shift produced by increasing [Ca]o or decreasing [Ca]i has been described on other preparations. It is then supposed that the electrical field of the membrane is modified by the gradient of double cations.

Animals↗
PubMed1975

Evidence for a transient potassium membrane current dependent on calcium influx in crab muscle fibre.

1. Voltage-clamp experiments were achieved on crab muscle fibre with the double sucrose-gap technique. 2. The accuracy of the imposed voltage has been controlled with an impaled micro-electrode connected to an external circuit. 3. Step depolarizations elicit two kinds of records. In type I fibres, the initial current exhibits only an inward calcium component. In type II fibres, the initial current exhibits a hump, transient outward current, mixed with the calcium current; these fibres exhibit always action potentials with fast repolarization. 4. A potassium origin is suggested for this outward current, due to its dependence on [K]o and its inhibition by TEA. 5. In fibres with a composite initial current, the voltage dependence of the availability of the measured inward current appears complex. It can be shown to be the sum of a simple calcium inactivation (which is observed alone in TEA solution) and a fast potassium inactivation. This potassium conductance is nearly half-available at the resting membrane potential. 6. The origin of the transient outward current is tentatively described. Consecutive to a transient internal increase of calcium ions (due to the calcium current) its activation curve is shifted in an hyperpolarizing direction resulting in an increased activation for an apparent identical depolarization. 7. This fast outward current which overlaps the calcium inward current can account for the low amplitude and the variability of the electrical activity of crab muscle fibres.

Action Potentials↗