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Y Mounier

Publications and source records attributed to Y Mounier.

At least 37 records · Page 2Linked to original sources
PubMed1999

Time-dependent changes in myosin heavy chain mRNA and protein isoforms in unloaded soleus muscle of rat.

Time-dependent changes in myosin heavy chain (MHC) isoform expression were investigated in rat soleus muscle unloaded by hindlimb suspension. Changes at the mRNA level were measured by RT-PCR and correlated with changes in the pattern of MHC protein isoforms. Protein analyses of whole muscle revealed that MHCI decreased after 7 days, when MHCIIa had increased, reaching a transient maximum by 15 days. Longer periods led to inductions and progressive increases of MHCIId(x) and MHCIIb. mRNA analyses of whole muscle showed that MHCIId(x) displayed the steepest increase after 4 days and continued to rise until 28 days, the longest time period investigated. MHCIIb mRNA followed a similar time course, although at lower levels. MHCIalpha mRNA, present at extremely low levels in control soleus, peaked after 4 days, stayed elevated until 15 days, and then decayed. Immunohistochemistry of 15-day unloaded muscles revealed that MHCIalpha was present in muscle spindles but at low amounts also in extrafusal fibers. The slow-to-fast transitions thus seem to proceed in the order MHCIbeta --> MHCIIa --> MHCIId(x) --> MHCIIb. Our findings indicate that MHCIalpha is transiently upregulated in some fibers as an intermediate step during the transition from MHCIbeta to MHCIIa.

Animals↗
PubMed1999

Mechanisms of the UTP-induced tension in mammalian skeletal muscles.

The mechanisms of UTP-induced tension in human and rat skinned fibers were investigated using isometric tension recordings, electrophysiological techniques and biochemical methods. In fast-type fibers from rat extensor digitorum longus (EDL) the UTP-induced tension: a) required previous loading of Ca2+ into the sarcoplasmic reticulum (SR); b) was inhibited by previous exposure to caffeine; c) was abolished by functional disruption of the SR; d) was not affected by blockade of the SR Ca(2+)-release channels by ruthenium red or heparin; e) was prevented by spermidine. These data point to the SR as the target of UTP action and suggest a pathway of UTP-induced Ca(2+)-release independent of the ryanodine- or the IP3-sensitive Ca(2+)-release channels. Accordingly, UTP failed to stimulate the electrophysiological activity of ryanodine-sensitive channels, incorporated into lipid bilayers. We suggest that UTP-induced Ca(2+)-release might occur via the channel form of the SR Ca(2+)-ATPase. The UTP-induced tension in human slow-type fibers was not affected by the SR Ca2+ content or by disruption of the SR, but was accompanied by changes in the tension-pCa relationship, namely increase in maximum Ca(2+)-activated tension, and in apparent Ca(2+)-affinity of troponin. The UTP-induced tension in slow-type fibers from rat soleus was partially inhibited by Ca(2+)-depletion from, or by disruption of the SR, and was accompanied by changes in tension/pCa relationship, similar to those observed in human fibers. Both in skinned fibers and in isolated SR vesicles, UTP was less effective than ATP as a substrate for the SR Ca(2+)-ATPase. This effect might contribute to the UTP-induced tension.

Animals↗
PubMed1998

Uridine triphosphate-sensitive pathway of Ca2+ release from the sarcoplasmic reticulum of rat skeletal muscle fibers.

The pyrimidine nucleotide, uridine triphosphate (UTP), was tested with skinned skeletal muscle fibers in order to investigate the UTP-sensitive pathway of Ca2+ release from the sarcoplasmic reticulum. The presence of ryanodine (200 microM), ruthenium red (10 microM) or heparin (2.5 mg/ml) did not affect the tension elicited in the presence of UTP, demonstrating that the UTP-induced Ca2+ release involved neither ryanodine nor inositol triphosphate-sensitive channels. Drugs such as compound 48/80 or cyclopiazonic acid used to inhibit Ca2+-ATPase in its reverse function appeared to be, respectively, non-specific or without any inhibitory effect on the tension induced by UTP. Finally, the UTP-induced tension as well as the trifluoperazine-induced tension were abolished in the presence of spermidine (50 mM), supporting the hypothesis that the UTP-sensitive pathway of the SR Ca2+ release might occur through the uncoupled calcium ATPase.

Animals↗
PubMed1998

Single-channel properties of the sarcoplasmic reticulum calcium-release channel in slow- and fast-twitch muscles of Rhesus monkeys.

RyR1 is the main isoform of ryanodine receptor expressed in fast- and slow-twitch mammalian skeletal muscles although differences in Ca2+-release kinetics and properties have been reported. Single-channel measurements reveal that a large proportion (82%) of Ca2+-release channels measured in slow-twitch muscle preparations have properties similar to those of the Ca2+-release channels of fast-twitch preparations, i.e. the same conductance, an identical sensitivity to caffeine and a bell-shaped Ca2+ activation curve for pCa (-log10[Ca2+]) 7 to 3. A low proportion (18%) of Ca2+-release channels observed in preparations from slow-twitch muscles were characterized by a very high activity level. These channels were not inhibited at a millimolar concentration of Ca2+. Our data suggest that the different properties of Ca2+ release in slow- and fast-twitch muscles might not be related to intrinsic properties of the Ca2+-release channels of each type of muscle but rather to the co-expression of two isoforms of ryanodine receptor and the lower amount of Ca2+-release channels expressed in slow- than in fast-twitch muscles.

Animals↗
PubMed1998

Differential effects of a six-day immobilization on newborn rat soleus muscles at two developmental stages.

Our objective was to determine the effects of a six-day immobilization on the musculoskeletal system of the rat during postnatal development at two key periods when the states of innervation are known to be different. This work was undertaken on the soleus muscle since it is well known that postural slow muscles show marked changes after a period of disuse. Thus, the soleus muscle was immobilized in a shortened position either when the innervation was polyneuronal or monosynaptic, respectively from 6 to 12 and from 17 to 23 days. The muscle modifications were followed by ATPase staining and myosin heavy chain (MyHC) isoform identification using monoclonal antibodies and SDS-PAGE. The functional properties of skinned fibre bundles were established by calcium/strontium (Ca/Sr) activation characteristics. In control muscles the maturation was characterized by a progressive increase of adult MyHCs (I and IIA) concomitant with a decrease in both the MyHC neo and the Ca affinity. Between 6 to 12 days, immobilization of the limb induced an increase in histochemical type IIC fibres. Using antibodies we identified new fibre types, classified as a function of their MyHC isoform co-expression. We observed an increase in expression of both MyHC neo and Ca affinity. From 17 to 23 days, the immobilization induced an increase in Ca affinity and marked changes in the MyHC isoform composition: disappearance of MyHC neo and expression of the fast MyHC IIB isoform, which in normal conditions is never expressed in the soleus muscle. We conclude that an immobilization imposed during polyneuronal innervation delays the postnatal maturation of the soleus muscle, whereas when the immobilization is performed under monosynaptic innervation the muscle evolves towards a fast phenotype using a default pathway for MyHC expression.

Adenosine Triphosphatases↗
PubMed1998

Functional effects of uridine triphosphate on human skinned skeletal muscle fibers.

Chemically skinned human skeletal muscle fibers were used to study the effects of uridine triphosphate (UTP) on the tension-pCa relationship and on Ca2+ uptake and release by the sarcoplasmic reticulum (SR). Total replacement (2.5 mM) of adenosine triphosphate (ATP) with UTP (i) displaced the tension-pCa relationship to the left along the abcissae and increased maximum Ca(2+)-activated tension, both effects being larger in slow- than in fast-type fibers; (ii) markedly reduced Ca2+ uptake by the SR (evaluated by the caffeine-evoked tension) in both fiber types; (iii) had no effect on the rate of depletion of caffeine-sensitive Ca2+ stores during soaking in relaxing solutions; (iv) induced tension in slow- but not in fast-type fibers. The effects on the SR functional properties are consistent with the notion that UTP is a poor substitute for ATP as a substrate for the Ca ATPase pump and as an agonist of the ryanodine-sensitive Ca(2+)-release channel. The UTP-induced tension in human slow-type fibers is attributed to effect(s) of the nucleotide on the tension-pCa relationship of the contractile machinery. The present data reveal important differences between the effects of UTP on human versus rat muscle fibers.

Caffeine↗
PubMed1997

Functional effects of uridine triphosphate on the atrophied soleus muscle of rat after unloading.

The purposes of the study were to determine the effects of a pyrimidine nucleotide, the uridine triphosphate (UTP), on the contractile and histochemical properties of the soleus (SOL) muscle following disuse atrophy due to hindlimb unloading (HU) hypokinesia. UTP was injected either during the HU period (2 weeks) or later during the recovery period. In this latter condition, contractile and histochemical properties were studied after 5, 8, 11, and 15 days of spontaneous recovery. HU induced decreases in the SOL weight, force output (twitch and tetanic tensions), time to peak tension during the twitch, and the percentage of type I fibers. The injection of UTP during the HU period did not counteract the modification in speed-related properties, but the decrease in force output was partly counteracted and the proportion of type II C fibers was increased. When UTP was injected during the recovery periods, force-related properties recovered more rapidly. These results suggest that UTP may reduce the loss of force induced by atrophy.

Animals↗
PubMed1997

Contractile properties and myosin heavy chain composition of newborn rat soleus muscles at different stages of postnatal development.

This study was undertaken to correlate some of the functional characteristics with the myofibrillar composition in myosin heavy chain isoforms on newborn and adult rat soleus muscles. The following postnatal ages were chosen in order to determine the role of innervation in the establishment of the mature muscle phenotype: before (postnatal day 6), when (postnatal day 12), and after (days 17 and 23) the monosynaptic innervation appeared. The steady state of definitive innervation was controlled on adult muscles (i.e. approximately 13 weeks). Muscle maturation was followed by ATPase staining and fibre diversity was observed at postnatal day 12. The functional properties of skinned bundles isolated from newborn rats were determined by Calcium/Strontium activation characteristics (Tension/pCa and pSr relationships). From postnatal days 6 to 17, the Soleus bundles exhibited Calcium/Strontium activation characteristics intermediate between slow and fast fibre populations previously described in muscles. At day 23, the Calcium/Strontium activation characteristics of the soleus were closer to those of a slow type. Moreover, we observed a decrease in Ca affinity concomitant with the installation of the monosynaptic innervation, and an increase of the slow type I during postnatal development. Finally, this work reported a greater correlation between the Calcium/Strontium activation parameters and the myosin heavy chain isoform composition at the postnatal days when the mature monosynaptic innervation pattern occurred.

Animals↗
PubMed1997

Effect of bovine serum albumin on the calcium release channel of sarcoplasmic reticulum from rabbit skeletal muscle.

The effect of bovine serum albumin (BSA) on the activity of the calcium release channel of the sarcoplasmic reticulum from rabbit skeletal muscle was investigated using both tension recording from skinned fibres and electrophysiological recording of unitary channel currents from planar lipid membranes. BSA had no effect on the Ca2+ affinity of the contractile proteins, elicited no tension per se in Ca(2+)-loaded skinned fibres, but potentiated caffeine-induced tension. Maximum potentiation was observed with 0.05-0.5% BSA. BSA (0.1%) had no detectable effect on the basal activity of the Ca(2+)-release channel incorporated in lipid bilayer. However, channel stimulation elicited by either caffeine (2 mM) or ATP (60 microM) was further enhanced by BSA (0.1%), as indicated by significant increases in Po, the open probability of the channel. These results suggest that BSA can modulate the response of the skeletal muscle SR Ca(2+)-release channel to different activators such as caffeine and ATP.

Adenosine Triphosphate↗
PubMed1995

Structure-function relationship of soleus muscle fibres from the rhesus monkey.

Functional and structural properties of rhesus monkey skinned fibres were studied in order to examine the relationship between calcium/strontium (Ca/Sr) activation characteristics and protein composition. The fibres were classified according to their Ca/Sr affinity into slow (61%) and fast groups (39%). According to the myosin isoform composition, two additional hybrid types were defined. Thus, four profiles were characterized: two corresponding to slow (S) and fast (F) isoforms and two corresponding to a mixed proportion of slow and fast isoforms. They were called hybrid slow (HS) or hybrid fast (HF) based on the predominant myosin isoform. Tension/pCa parameters and maximal shortening velocities were determined. S fibres showed a higher pCa threshold and affinity as well as shallower slopes of their tension/pCa curve than did F fibres. HS and HF fibres exhibited tension/pCa curves which were positioned close to those of S and F fibres, respectively. No significant difference was observed between S and HS fibres or between F and HF fibres. Maximal shortening velocity values were higher for fibres expressing predominantly fast myosin isoforms. We suggest than when both S and F isoforms of myofibrillar proteins are expressed in a muscle fibre, the functional properties are mainly governed by the predominant isoform.

Animals↗
PubMed1995

Effects of uridine triphosphate on skinned skeletal muscle fibers of the rat.

Chemically skinned muscle fibers from rat extensor digitorum longus muscle were used to study the effects of uridine triphosphate (UTP) on Ca2+ uptake and release by the sarcoplasmic reticulum (SR) and on Ca2+-activated tensions. Total replacement (2.5 mM) of adenosine triphosphate (ATP) with UTP (i) increased submaximal Ca2+-induced tension (pCa 6.2-5.8) but diminished Po, the maximum tension elicited by pCa 4.2, by ca. 15%, (ii) markedly reduced Ca2+ uptake by the SR (evaluated by caffeine-elicited tension); and (iii) induced tension in Ca2+-loaded fibers. The UTP-induced tension averaged 55% of Po and its rates of development and decay were considerably slower than those of caffeine-evoked tension. The UTP-induced tension (i) depended on the Ca2+-loading conditions; (ii) was reversibly blocked by brief (15 s) exposures of Ca2+-loaded fibers to 5 mM EGTA or by pretreatment with caffeine; (iii) was abolished by functional disruption of the SR with the nonionic detergent Brij-58; and (iv) persisted after blockade of the SR Ca2+ release channels with ruthenium red. Exposure of Ca2+-loaded fibers to UTP depressed the tension elicited subsequently by caffeine, and enhanced the rate of depletion of caffeine-sensitive Ca2+ stores during soaking in relaxing solutions containing 5 mM EGTA. The UTP-induced tension is attributed to increased release of Ca2+ from the SR, via a ruthenium red insensitive pathway(s), combined with reduced Ca2+ uptake by the SR and increased Ca2+ affinity of the contractile proteins.

Adenosine Triphosphate↗
PubMed1994

Influence of chronic stretching upon rat soleus muscle during non-weight-bearing conditions.

Morphological, contractile and histochemical properties as well as the myosin heavy chain (MHC) composition of rat soleus muscles were studied after 14 days of non-weight-bearing (NWB) and after immobilization of the foot in dorsiflexion of NWB rats. Significant reductions in soleus mass, fibre sizes and tetanic tension were found after 14 days of NWB. Furthermore, a transformation of the slow-twitch soleus muscle towards a faster type was characterized by a decrease in twitch time parameters, an increase in the fast-twitch type IIA fibre proportion and an increase in fast-twitch type MHC isoforms. Our results showed that the immobilization of the soleus muscle in a lengthened position during NWB not only prevented the loss of muscular mass and force output, but also counteracted the slow to faster shift in contractile and phenotypical parameters normally associated with NWB conditions.

Animals↗
PubMed1993

Effects of chronic electrostimulation on rat soleus skinned fibers during hindlimb suspension.

In order to counteract the changes of the contractile properties of the rat soleus occurring during 10 days of hypokinesia-hypodynamia, due to hindlimb suspension (HS), two different patterns of electrostimulation were applied to the tibial nerve. The contractile properties of single chemically skinned muscle fibers were investigated using the tension-pCa relationship characteristics, the similar or different calcium and strontium affinities, and by measuring the P/tmax kinetic parameters. Our results showed that a pattern similar to firing rates of motoneurons innervating slow twitch muscles inhibited the slow to fast fiber changes observed during HS, whereas a pattern similar to firing rates of motoneurons from fast twitch muscles seemed to favor these changes. Since neither pattern maintained the isometric contractile force developed by the soleus fibers, we concluded that the decrease in mechanical strains imposed on the muscle during unloading was the main factor for the development of atrophy, while the kinetic changes might be predominantly modulated by the nervous command.

Animals↗
PubMed1993

Functional adaptation of different rat skeletal muscles to weightlessness.

The adaptation to weightlessness of two postural muscles, the slow soleus (SOL) and the fast gastrocnemius lateralis (GL), and a fast muscle used in movements, the extensor digitorum longus (EDL), was studied on five adult Wistar rats. The animals exposed to 14-day spaceflight aboard COSMOS 2044, designated as flight (F), were compared with synchronous (S) animals. The experiments were performed on single skinned fibers whose functional properties were studied. After weightlessness, the SOL exhibited two populations of fibers according to their Sr2+ affinities: 40% remained slow (Fs) and 60% acquired fast-type properties (Ff). Both S and F GL and EDL showed a single distributed population of fast fibers. SOL fibers atrophied insofar as they showed a significant reduction in fiber diameter and absolute maximal tension Po (mg) but not in Po expressed in kg/cm2. GL fibers showed no change in fiber diameter but a decrease in Po in mg and kg/cm2. EDL fibers were not atrophied by weightlessness. The tension/Ca concentration relationships of the Ff SOL and F GL fibers were shifted to the right, indicating a decrease in their Ca2+ affinity. An increase in the contraction kinetics was described for the SOL fibers after weightlessness, whereas no significant modification was found for the GL and EDL. Collectively, the data suggested that the adaptive changes subsequent to weightlessness were more dependent on the muscle function than on the fiber type, since both postural SOL and GL were modified.

Adaptation, Physiological↗
PubMed1992

Ca2+ movements in sarcoplasmic reticulum of rat soleus fibers after hindlimb suspension.

The functional capacity of skeletal muscle sarcoplasmic reticulum (SR) was examined in the slow soleus of rats submitted to 15 days of disuse produced by hindlimb suspension (HS). By using caffeine-induced contractions of single skinned fibers, Ca2+ uptake, Ca2+ release, and passive Ca2+ leakage through the SR membrane were investigated. In the SR of atrophied muscles, the amounts of Ca2+ uptake and Ca2+ release were significantly higher than in the control muscles and were close to those found for a fast muscle, the plantaris. Moreover, the study of the Ca2+ leakage showed that the time required to empty the SR previously loaded with Ca2+ was reduced by a factor of two after HS. Such disturbances of the Ca2+ movements in the SR suggested that alterations of the SR membrane occurred after HS. The results supported the idea that after hindlimb unweighting the slow soleus muscle acquired SR properties that were very much like those of a faster muscle.

Animals↗
PubMed1991

Effects of short spaceflights on mechanical characteristics of rat muscles.

The aim of this study was to investigate the contractile protein characteristics after 5-day (Cosmos 1514) and 7-day (Cosmos 1667) spaceflights. The experiments were performed on skinned fibers from the soleus, gastrocnemius lateralis, and plantaris muscles isolated from Wistar rats. A reduction in fiber diameter might explain the decrease in the maximal tension in the soleus, whereas this tension was unaltered in the gastrocnemius and the plantaris. Moreover the calcium sensitivity of the myofilament appeared modified in the soleus and in the gastrocnemius: The tension/pCa relationships were shifted toward higher calcium concentrations, indicating a decrease in the apparent calcium binding constant of the troponin C. The tension/pCa relationship appeared unaltered in the plantaris after spaceflight. Finally, the studies of the time to reach a steady tension indicated an increase in the rate of force development in the soleus and, on the contrary, a slowing down in the plantaris. No change in the gastrocnemius was found. The results were analyzed with references to the different muscle functions in disuse atrophy.

Animals↗