Interrelationships of contraction time, Vmax, and myosin ATPase after spinal transection

Abstract

Interrelationships of selected mechanical and biochemical properties of hindlimb extensor muscles following low thoracic cord transection were studied. Kittens were spinalized (Sp) at 2 wk and maintained for 6-12 mo. Some Sp animals were exercised (Sp-E) on a treadmill 25-30 min/day, 5 days/wk. In situ contractile properties of the slow-twitch soleus (SOL) and fast-twitch medical gastrocnemius (MG) muscles of normal (N), Sp, and Sp-E cats were determined. Exercise did not affect most parameters; thus Sp and Sp-E groups are considered collectively. The cross-sectional areas (CSA) of the SOL and MG decreased by 43 and 32%, respectively. Specific tension (tension/CSA) was maintained in the SOL but decreased (P less than 0.05) in the MG. Contraction time (CT) and half-relaxation time were significantly shorter in the SOL but unchanged in the MG. Maximum shortening velocity (Vmax) and myosin ATPase (mumol X mg-1 X min-1) increased (P less than 0.05) in the SOL of both groups and the MG of Sp. Frequency-tension responses of both muscles shifted toward that resembling a "faster" muscle. These results substantiate the existence of relatively independent regulatory mechanisms for Vmax and CT and show that myosin ATPase levels are more closely related to Vmax than CT. Although the changes in the SOL were consistent with the hypothesis that slow fibers are converted to fast, the elevated Vmax and myosin ATPase of the MG suggest that significant changes also occur within a "fast" fiber-type category.

Skeletal muscle fibre type transformation following spinal cord injury

“…We obtained data over a wide range of post SCI time periods (0.5 ± 219 months) to discern how rapidly a fundamental muscle property (MHC isoform) was altered by SCI. The MHC isoform of a ®bre was chosen as a property index because of the following reasons: (1) Nearly all adult normal muscle ®bres express only one MHC isoform; 23 (2) The isoform composition of adult normal muscle appears to be stable; 23 (3) In normal adult muscle the MHC isoform is related to the standard histochemical based ®bre typing classi®cation criteria predicated on the pH sensitivity of myo®brillar ATPase and histochemically determined Type I ®bres have the slow MHC isoform, Type II ®bres and fast MHC isoform, and Type C ®bres co-express both MHC isoforms; 24 (4) The MHC isoform has been shown to have predicable interrelationships with other muscle properties under control conditions and in various models of muscle perturbation, 12,19 and, (5) Immuno¯uorescence techniques are available for the determination of the MHC isoform composition of single ®bres. 22 This provides a sensitive method by which to study changes in this muscle property after SCI.…”

“…This muscle property was chosen because of its fundamental importance to muscle function and its well de®ned interrelationships with other muscle properties. 12,19 Further, the immuno¯uorescent techniques used provide a more sensitive index of change than was possible in previous studies on SCI muscle. Our ®ndings suggest that fundamental muscle properties are altered much earlier than has been previously reported following SCI.…”

Cost of transport is increased after cold exposure inMonodelphis domestica: training for inefficiency

“…The muscle was allowed to recover for at least 2·min between each tetanus. The recordings of tetanic contractions from P 0 to minimal loading were used to calculate v max using the Hill equation described in Roy et al (1984). Force and speed (dL/dt) were determined for each point, then plotted as y=(P 0 -P)/v vs x=P, where P is the measured force and v is the calculated speed.…”

Effect of Altered Thyroid State on the in situ Mechanical Properties of Adult Cat Soleus

“…After 4 months of thyroid hormone manipulation, the in situ mechanical properties of the soleus were determined as described previously [Roy et al, 1984[Roy et al, , 1996. The cats were anesthetized with sodium pentobarbital (35 mg/kg, i.p.)…”

“…As previously described [Roy et al, 1984[Roy et al, , 1996, a modification of a pneumatic isotonic lever was used to measure all isometric and isotonic mechanical properties. The distal tendon of the soleus was attached in situ by a wire (see above) to a lever arm on which force and displacement gauges were mounted.…”