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[Cathepsin activity of skeletal muscle and myocardial myofibrils after exposure to weightlessness and G force].

The rats flown on board Cosmos-605 and exposed to a synchronous experiment for 22 days showed an increased activity of myofibrillar cathepsins in skeletal muscles of different groups. In the flight rats the increase was greater than in the synchronous ground-based animals. This suggests a significant effect of weightlessness on the cathepsic activity. The parameter was partly normalized at R + 25 or 26. The exposure of rats to accelerations of 4 and 5 G for 20 min daily during 2 weeks also increased the cathepsic activity of skeletal and myocardial myofibers. The parameter returned to normal a month after completion of acceleration exposures. Thus, changes in the proteolytic activity of myofibers of different muscles induced by weightlessness and acceleration are reversible. The significance of changes in the muscle tension as related to the mechanism of stimulation of proteolytic reactions is discussed.

Animals↗
PubMed1980

[Myofibrils and autophagic vacuoles during atherosclerotic ischemia in man].

The various cases of ultrastructural changed in human skeletal muscles in an ischemic state have been examined. From the examination of the material used, it results that in these muscles, certain myelinic figures and autophagic vacuoles are present. These figures are at times linear and in order, whereas in other regions the lamellar components reveal to be disorganized. In many cases, the larger myelinic figure is near the nucleus, almost next to it. Even electron-dense membranes that surround crystalline inclusion placed between the myelinic figures have been observed. The presence of autophagic vacuoles and myelinic figures is important. The cause of this presence is probably due to a different state of degeneration of the different regions in which these vacuoles are or are not present. Both the autophagic vacuoles and the myelinic figures are found associated with the proteolysis of the tissues. Because of these observations, it has been hypothesized that these changes are a consequence of degeneration. Nonetheless, these changes could be caused by both ischemia and atrophy caused by denervation contemporarily, when the above happens in subjects forced to a long-term immobile state, or in an advanced state of gangrene, or during contemporary and associate phlogistic processes with deficient peripheral nervous structures.

Aged↗
PubMed1975

[The effect of cations on the contraction of myofibrils in the striated muscles of crabs].

Myofilaments have been prepared from crab legs according to a technique derived from that of F.J. Julian (1971). Tension variations have been recorded while the isolated fiber was submitted to the action of different saline solutions. As expected, it could be confirmed that the tension mainly depends on the content in Ca++ and Mg++ ions and in ATP. Our results have also shown that monovalent ions (Na+ and K+) when added separately, produce an important tension increase wheras their simultaneous addition or withdrawal modifies the tension only slightly.

Adenosine Triphosphate↗
PubMed1997

Ca2+ activated myosin-ATPase in cardiac myofibrils of rainbow trout, freshwater turtle, and rat.

The Ca(2+)-activated myosin-ATPase and its dependence on hypoxia were assessed in freshwater turtle, rainbow trout, and in some cases rat. At 20 degrees C and pH 7.3, the maximal ATPase activity was (mean +/- SEM): turtle 0.040 +/- 0.003, trout 0.090 +/- 0.005, and rat 0.12 +/- 0.004 mmol*min-1*g-1 myofibrillar dry weight. The turnover number was about three times lower for turtle than for trout. Trout is typically active at lower temperatures than turtle, and its myosin-ATPase activity was about three times lower at 10 degrees than at 20 degrees C. Addition of 12 mM phosphocreatine showed that the myosin-ATPase activity covered by myofibrillar creatine kinase was 22 +/- 2% for turtle, 14 +/- 2% for trout, and 69 +/- 5% for rat. At pH 6.8 relative to 7.3, the maximal M-ATPase activity was the same, whereas the Ca(2+)-sensitivity decreased, and more so for trout than for turtle. This difference disappeared, when trout myocardium was examined at 10 degrees C. P(i) (15 mM) affected neither maximal activity nor Ca(2+)-sensitivity. ADP, however, reduced maximal myosin-ATPase activity, and more so in trout than in turtle. In conclusion, the "slow"-type myosin, the low sensitivity of acidification and ADP, and the high creatine kinase/myosin-ATPase ratio in turtle relative to trout accord with the well-known ability of turtle myocardium to work during hypoxia. However, the difference in living temperature between turtle and trout obscures the situation (e.g. inclusion of rat data suggests that the creatine kinase/myosin-ATPase ratio is related to temperature.

Adenosine Diphosphate↗
PubMed1997

A theoretical model of some spatial and temporal aspects of the mitochondrion creatine kinase myofibril system in muscle.

We describe a model of mitochondrial regulation in vivo which takes account of spatial diffusion of high-energy (ATP and phosphocreatine) and low-energy metabolites (ADP and creatine), their interconversion by creatine kinase (which is not assumed to be at equilibrium), and possible functional 'coupling' between the components of creatine kinase associated with the mitochondrial adenine nucleotide translocase and the myofibrillar ATPase. At high creatine kinase activity, the degree of functional coupling at either the mitochondrial or ATPase end has little effect on relationships between oxidative ATP synthesis rate and spatially-averaged metabolite concentrations. However, lowering the creatine kinase activity raises the mean steady state ADP and creatine concentrations, to a degree which depends on the degree of coupling. At high creatine kinase activity, the fraction of flow carried by ATP is small. Lowering the creatine kinase activity raises this fraction, especially when there is little functional coupling. All metabolites show small spatial gradients, more so at low cytosolic creatine kinase activity, and unless there is near-complete coupling, so does net creatine kinase flux. During workjump transitions, spatial-average responses exhibit near-exponential kinetics as expected, while concentration changes start at the ATPase end and propagate towards the mitochondrion, damped in time and space.

Animals↗
PubMed1994

Theory and observation of spontaneous oscillatory contractions in skeletal myofibrils.

At low levels of activation, an isometrically-held myofibrillar preparation on the descending limb may exhibit persistent oscillations of period 1-6 s in tension and sarcomere lengths. We propose a sarcomeric theory of spontaneous oscillatory contraction, based on the phenomena of force creep and delayed length activation. The time delay leads to oscillations and controls their period. A computer model using these ideas simulates spontaneous oscillatory contraction for fixed-end fibres only if isometric tension capacity varies slightly along the fibre. The form of this inhomogeneity controls a diversity of spontaneous oscillatory contraction behaviour: the tension waveform can vary from large and sinusoidal to small-amplitude pulses or chaotic behaviour, and these variations are observed in slow-twitch soleus fibres from the same animal (rat). The model predicts that oscillatory and quiescent regions coexist in the fibre, with large-amplitude sawtooth waveforms in sarcomere length in the former as observed. It can also generate travelling-wave structures, similar to those found by the Tokyo group, in oscillating regions when there is a spatial gradient in isometric tension capacity. Phase discontinuities in sarcomere length occur near the oscillatory-quiescent boundary. Predictions for the Ca2+ concentrations and sarcomere lengths in which spontaneous oscillatory contraction occurs and for differences in the spontaneous oscillatory contraction frequencies of fast- and slow-twitch fibres compare well with experiment. Spontaneous oscillatory contraction is also predicted under isotonic conditions.

Animals↗
PubMed1993

Isometric tension exerted by a myofibril of the frog at 0 degree C: geometrical considerations.

For a number of years, the isometric force per myosin head has been taken as 1 pN by the authors who studied in vitro movement. This value was deduced from the value of the isometric tension exerted by a living or a skinned fibre at approximately 0 degree C and for the frog (1-3 kg cm-2). Starting from an isometric tension exerted by a single unit cell of approximately 10 kg cm-2, it has been shown that the isometric force per myosin head is (8 +/- 1)pN. The value of approximately 10 kg cm-2 was deduced from theoretical and semi-empirical reasonings independent of the mechanical roles of the crossbridges. Here, we discuss this latest value by using simple geometrical considerations.

Animals↗