Georges Maréchal

Increased susceptibility of EDL muscles from mdx mice to damage induced by contractions with stretch.

SummaryAbsence of dystrophin in mdx muscles may render the muscle more susceptible to damage when submitted to high stress levels. To test this, typically slow (soleus) and fast (EDL) limb muscles of dystrophic (mdx) and normal (C57BL/10) mice were submitted (in vitro) to a series of isometric contractions, followed by a series of contractions with stretches. Muscle injury was assessed by monitoring the force signal. Membrane damage was evaluated by bathing the muscle in Procion Red, a dye that does not penetrate intact fibres, and subsequent analysis by light microscopy. After isometric contractions, only a very small force drop (<3% of maximal isometric force) was observed which indicated that no injury had occurred in soleus and EDL muscles in either mdx or C57 strains. After contractions with a stretch, a force drop of 10% was observed in soleus muscles from both strains and in EDL muscles from C57 mice. However, in mdx mice EDL muscles displayed an irreversible force drop of 40–60%. Histological analysis of the muscles indicates that force drop is associated with membrane damage. These results show that EDL muscles from mdx mice are more vulnerable than their controls, supporting the structural role hypothesis for dystrophin. Furthermore, they suggest that contractions with stretches may contribute to the muscle damage and degeneration observed in DMD-patients.

The Force-velocity Relation of the Rabbit Inferior Oblique Muscle Influence of Temperature

The contractile properties of the rabbit inferior oblique muscle (IO) were studied in vitro with direct stimulation at temperatures between 20 and 35°C. Isovelocity releases were used to determine the force/ velocity relation. Cooling the muscle from 35°C to 20°C increased contraction and half-relaxation times of single twitches with a temperature coefficient (Q10) of 0.4, but did not affect significantly the twitch tension. The tetanic tension increases with increasing temperature (Q10=1.32). Cooling decreased the maximum shortening velocity of the IO with a Q10 of 1.6 and the maximum mechanical power with a Q10 of 2.3. At 35°C, the maximum speed of shortening of the muscle (19±2 muscle lengths/s, mean ± SEM) corresponded to a maximum shortening velocity of the sarcomeres of 57±6 μm/s. This value is similar to data obtained for extraocular muscles (EOM) of smaller rodents (mice and rats). In comparison with mammalian limb muscles the isometric and force-velocity properties of mammalian EOM appear to be virtually independent of the size of the animal. Thus, IO is a fast-twitch muscle endowed with a maximum velocity of shortening higher than that of fast-twitch skeletal muscle, but using a tetanic mechanical power lower than that produced by slow-twitch muscle: the combination of these properties makes it ideally suited to move an ocular globe of low mass at high velocity.

Force-velocity relation and isomyosins in soleus muscles from two strains of mice (C57 and NMRI)

We compared soleus muscles from two strains of mice, NMRI and C57. Soleus muscles from NMRI mice produced slower twitches and lower maximum tetanic force (Fo) but higher maximum tetanic stress (So), (owing to their smaller weight). Their Hills velocity constant (b) was lower, but their force constant (a/So), their maximum velocity of unloaded shortening (Vu) and their maximal mechanical power (Pmax) were similar. All soleus muscles contained two isomyosins (SM2 and IM) and the two myosin heavy chains (MHC1 and MHC2A) corresponding to type I fibres and type IIA fibres; however, soleus muscles from NMRI strain had higher proportions of isomyosin SM2 and of myosin heavy chain 2A. Regression equations were computed between the mechanical variables and the myosin heavy chain content. Using a simple hypothesis, the results were used to estimate the mechanical properties of type I and type IIA fibres. We conclude that type IIA fibres from soleus muscle are mechanically more similar to slow-twitch type I fibres than to fast-twitch type II fibres. The results also suggest a hypothesis to account for the diversity of isomyosins, by a matching diversity of mechanical properties based on a separate physiological control of the three factors that control Pmax.

Lack of myoblasts migration between transplanted and host muscles of mdx and normal mice.

SummaryExtensor digitorum longus muscles of normal mice (C57BL/10ScSn hereafter called C57) were orthotopically transplanted into dystrophin-deficient mice (mdx) and reciprocally, mdx Extensor digitorum longus muscles were transplanted into C57 mice. After an initial phase of degeneration, transplanted muscles regenerate nearly completely, as evaluated from the maximum isometric force of muscles isolated 60 days after the surgery. In other similar experiments, instead of isolating the grafted muscles, we excised the antero-external muscles of the leg, including the grafted muscle. Cryostat cross-sections at three levels along the muscles were immunostained with an anti-dystrophin antibody. No muscle cells of dystrophin-deficient muscles grafted into normal mice took the antibody except a few ‘revertant’ fibres, while all the muscle cells of the normal host were immunostained. Reciprocally, all the muscles cells of normal grafts were stained, whilst no antibody stained the cells of the surrounding muscles of the dystrophin-deficient host. These experiments show that very few if any of the myoblasts or muscle precursor cells, active during the regeneration of grafted muscle, migrate into the adjacent muscles. These results could be explained by the absence, in our work, of injuries of the grafted and adjacent host muscles epimysium and the absence of extensive inflammatory reactions. This lack of myoblast mobility suggest that when myoblast transfer is applied to muscle therapy, it will be necessary to inject myoblasts within each muscle to obtain an efficient treatment.

Bioluminescence and luminescent fish in the Strait of Messina from the mesoscaph “Forel”

Light irradiance was measured at 430, 470 and 500 nm aboard the mesoscaph “Forel” in the Strait of Messina from the surface to 550 m depth in May 1979. The underwater light regime is partly due to the downwelling residual sunlight and partly to bioluminescence. An intense bioluminescence is localized at about 450 m at midday and moves upwards in the evening to reach an area extending from 100 m depth to the surface late in the evening. Two types of luminescence were observed: one associated with luminescent organisms and another diffuse, probably due to bacteria. Three types of luminescent fish were recognized, namely Argyropelecus hemigymnus, myctophids and Cyclothone braueri, and their time and space distribution were studied. While myctophids were encountered from the surface (21:00 hrs) to 550 m depth (16:00 hrs), A. hemigymnus were only observed between 180 m (19:45 hrs) and 500 m (12:15 hrs), and C. braueri between 330 m (16:00 hrs) and 500 m (19:00 hrs). The results do not show a significant relation between the absolute ambient light intensity and the time or the depth where the fish were observed.

Luminescence of Argyropelecus Photophores Electrically Stimulated

Abstract o 1. Isolated photophores of the living bathypelagic fish Argyropelecus hemigymnus respond to a strong (25–80 V) and long (4–15 msec) electrical stimulus by a brief flash emission (F response). 2. Weaker and shorter stimuli are subthreshold, but when repeated at a frequency equal to or higher than one per second, the photophores respond by a slow light emission (S response); it is characterized by a long emission latency time, at least 2 sec duration and by a progressive increase in the rate of light production during the stimulation period. The maximal amplitude of the response is more than 300 times lower than the response of the photophore of the epipelagic luminescent fish Porichthys. 3. A train of strong (35V) and long stimuli (4 msec) applied at high frequency (100/sec) quench temporarily the luminescence of spontaneous luminescent photophores. The inhibitory response is reversible: after the end of stimulation, the light production returns to the level recorded before the stimulation. 4. The inhibitory response to electrical stimulation is tentatively explained either by the presence of an inhibitory nervous system or by the liberation of an excess of adrenalin, the possible natural neuromediator that inhibits luminescence of isolated photophores at high concentration.

Time course of regeneration of minced frog muscles estimated by the level of energetic substrates.

Summary1.Gastrocnemius muscles of frogs have been excised, chopped and put back into the leg.2.The weight of the implanted muscles increases until the 8th day after the operation and then decreases to 1/3 of that of the control by the 30th day.3.The inulin space is twice as high in regenerating muscle as in the unoperated controls.4.Adenosine nucleotides are in an enzymatic equilibrium set by the ratio creatine/phosphorylcreatine during regeneration of the muscle.5.Glycolytic intermediates (hexose monophosphate, fructose-1,6-diphosphate, α-glycerophosphate and lactate) have been measured during the course of muscle regeneration up to the 30th day. The results suggest that the glycolysis of regenerating muscle is very active.6.The total creatine (sum of creatine and phosphorylcreatine) is very low after the operation: 5% of that of the controls; it rises sharply after the 8th day, and reaches 30% of that of the control on the 30th day.7.The amount of total creatine seems proportional to the progress of the muscle regeneration. It is suggested to use this substance as a biochemical reference for biochemical works on muscle regeneration.

Luminescence of Chauliodus photophores by electrical stimulation

Abstract 1. 1. Photophores isolated from living specimens of the bathypelagic fish Chauliodus sloanei emit bright flashes or luminus when they are electrically stimulated. 2. 2. Anodic stimuli of long duration (4–8 msec) and high strength (50 V) evoke quick flashes (10–130 10 6 quanta/sec) that fuse in a erratic way when the frequency of stimuli is higher than 2/sec. 3. 3. Anodic stimuli of short duration (1 msec) and low strength (10 V) evoke slow flashes that fuse together in a “luminus” when the frequency of stimuli increases up to 4/sec. 4. 4. The “luminus” response is characterized by a peak of light developed within 2 sec after the beginning of the electrical stimulation; afterwards, the light decreases to reach a constant level of light within about 10 sec.

Transient changes in the force-velocity relationship during tetanic contractions of frog sartorius muscles, normal or poisoned with 1-fluoro-2,4-dinitrobenzene.

Summary1.Frog sartorius muscles were tetanized for two seconds six times at two minute intervals, at 0°C; after the tension was fully developed at constant length, the muscles were released for two milimeters at constant velocity with an ergometer.2.As a result of the repetition, the isometric forcePm decreases by about 3–5% tetanus for the normal muscles. This effect is enhanced by about 50% after poisoning with 1-fluoro-2,4-dinitrobenzene (FDNB).3.The force maintained during the release (Pr) decrease still more than the isometric tension (Pm). The ratioPr/Pm decreases by approximately 1% per tetanus. This second effect of the repetition is not affected by the speed of shortening, but is enhanced about four-fold by FDBN.4.These results seem to require that the externally recorded isometric forcePm is equal to the force produced internally by the contractile protein, but that the force recorded during the releasePr is less than that produced by the contracting proteins by an amount equal to the friction between myofilaments which must be overcome in order that the muscle can shorten.

Unexpected Effects of Selected Fungicide Treatments On the Acid Content of Golden Delicious and Jonagold Apples

Abstract Several fungicide treatment schemes were assayed on ‘Golden Delicious’ and ‘Jonagold’ apples. The total content of free acids (measured by titration) and the contents of each of the main free acids (malic, citric, fumaric, syringic) plus their salts (measured by gas liquid chromatography of the silylated samples) in the freshly harvested apples were measured and compared to those obtained with the corresponding untreated apples (control). The fungicide treatments generally decreased the content of each of the free acids plus their salts, and of the total of free acids in the ‘Golden Delicious’ apples; the same fungicide treatments had no effect, or slightly increased the concentration of each of the free acids plus their salts and of the total of free acids, in the ‘Jonagold’ apples. However, the contents of citric acid plus its salts were generally increased by the fungicide treatments in both ‘Golden Delicious’ and ‘Jonagold’ apples.