ABSTRACT
The molecular mechanism of violation of the contractile function of skeletal muscles caused by oxidative damage to myosin is not fully understood. Using permeabilized fibres from fast (m. psoas) and slow (m. soleus) rabbit muscles, we studied the effect of myosin oxidation on the mechanism of force generation and its calcium regulation. It was found that this treatment simultaneously reduces the maximum force and fibers stiffness without affecting their calcium sensitivity. This suggests that the mechanism of oxidation-related impairment the force-generating ability of fibers consists in suppression of myosin cross-bridges formation and does no affect the characteristics of actin-myosin interaction.
Subject(s)
Calcium/metabolism , Hydrogen Peroxide/pharmacology , Isometric Contraction/drug effects , Muscle Fibers, Fast-Twitch/drug effects , Muscle Fibers, Slow-Twitch/drug effects , Myosins/chemistry , Actins/chemistry , Animals , Dithiothreitol/pharmacology , Hydrogen Peroxide/antagonists & inhibitors , Isometric Contraction/physiology , Kinetics , Muscle Fibers, Fast-Twitch/physiology , Muscle Fibers, Slow-Twitch/physiology , Octoxynol/pharmacology , Oxidation-Reduction , Permeability , RabbitsABSTRACT
Tension in contracting muscle fiber under conditions of ramp stretching rapidly increases, but after reaching a critical stretch Pc sharply decreases. To find out the cause of these changes in muscle fiber tension, we stopped stretching before and after reaching Pc and left the fiber stretched for 50 msec. After rapid tension drop, the transient tension rise not accompanied by fiber stiffness increase was observed only in fibers heated to 25°C and stretched to Pc. Under other experimental conditions, this growth was absent. We suppose that stretch of the fiber to Pc induces transition of stereo-specifically attached myosin heads to pre-power stroke state and when the stretching is stopped, they make their step on actin and generate force. When the tension reaches Pc, all stereospecifically attached myosin heads turn out to be non-stereospecifically, or weakly attached to actin, and are unable to make the force-generating step.
Subject(s)
Actins/physiology , Isometric Contraction/physiology , Muscle Fibers, Skeletal/physiology , Muscle Stretching Exercises , Myosins/physiology , Animals , Biomechanical Phenomena , Culture Media/chemistry , Elasticity , Models, Biological , Rabbits , Tissue Culture TechniquesABSTRACT
The temperature dependence of force, maximal shortening velocity and power of maximally activated single permeabilized fibers from fast and slow muscles of the rabbit were recorded in a temperature range from 10 to 35 degrees C with 5 degrees C step. It was found that temperature dependence of force of both types of fibers is identical. Averaged maximal shortening velocity in the slow fibers, unlike the fast fibers, had no statistically significant temperature dependence that is not in agreement with the data obtained on intact rat muscle fibers and in an in vitro motility assay. However maximal shortening velocity in each individual slow fiber did depend on temperature. The temperature dependence of power of the slow fibers was lower than that of the fast ones. Because of large data scattering the average temperature dependence of power of the slow fibers was significantly lower than that in individual slow fibers.
