Neural influence on slow muscle properties: inactivity with and without cross-reinnervation.
The effects of altering (cross-reinnervation, CR) and/or eliminating (spinal isolation, SI) the activation-dependent neural input to the cat soleus for 8 months on its mechanical and biochemical properties were determined. The percent fast fibers was 0, 27, 38, and 54% for normal control (NC), NC-CR, SI, and SI-CR cats. Calcium-activated whole muscle myofibrillar adenosine triphosphatase activity was higher in SI-CR and NC cats. Isometric twitch speed properties and frequency of stimulation:tension response were faster in all experimental groups compared to NC. Maximum twitch and tetanic (Po) force, physiological cross-sectional area (PCSA), and specific tension (Po/PCSA) were unaffected in NC-CR cats, but reduced in SI and SI-CR cats. The soleus was more fatigable in SI-CR compared to NC cats. Alpha-glycerophosphate dehydrogenase activity was higher in all experimental groups compared to NC. All eight parameters reflecting the type of muscle were shifted toward those observed in a "faster" muscle in SI-CR vs. SI cats. These data suggest that electrically silent motoneurons can influence type-related skeletal muscle properties.
Roy
R R
RR
Brain Research Institute, University of California, Los Angeles, 90095-1761, USA.
Eldridge
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L
Baldwin
K M
KM
Edgerton
V R
VR
D000818:Animals; D001835:Body Weight; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002415:Cats; D004558:Electric Stimulation; D005260:Female; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism; D007551:Isotonic Contraction; D009121:Muscle Denervation; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology*; D009124:Muscle Proteins / Q000032:analysis; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology; D009210:Myofibrils / Q000201:enzymology; D009474:Neurons / Q000502:physiology; D012016:Reference Values; D013116:Spinal Cord / Q000502:physiology*
D009124:Muscle Proteins; D005993:Glycerolphosphate Dehydrogenase; D000252:Calcium-Transporting ATPases