AJP - Cell Physiology, Vol 259, Issue 3 C507-C514, Copyright © 1990 by American Physiological Society
Enzymatic plasticity of medial gastrocnemius fibers in the adult chronic spinal cat
B. Jiang, R. R. Roy and V. R. Edgerton
Brain Research Institute, University of California, Los Angeles 90024-1564.
The metabolic plasticity of single fibers in adult cat medial gastrocnemius
(MG) 6 mo after complete spinal cord transection (Sp) at T12-T13 was
studied. Some Sp cats were trained to weight support (Sp-WS) 30 min/day
beginning 1 mo posttransection. Cross-sectional area, succinate
dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (GPD), and
myofibrillar adenosinetriphosphatase (ATPase) activities were determined in
fibers identified in frozen serial sections. Fibers were categorized as
light or dark based on myosin ATPase staining, alkaline preincubation. The
percentage of dark ATPase fibers was higher in Sp and Sp-WS (approximately
85%) than in control (approximately 60%). All dark ATPase fibers reacted
positively to a fast myosin heavy chain monoclonal antibody. In both spinal
groups, a higher percentage of dark ATPase fibers reacted to both fast and
slow myosin heavy chain antibodies than in controls. Neither Sp nor Sp-WS
cats showed fiber atrophy. Compared with control, SDH activity was
decreased in both fiber types of Sp cats. Daily weight-support training
ameliorated this adaptation. There were no differences among the three
groups in mean GPD and ATPase activities for either fiber type. There was a
slight tendency, however, for spinal cats to have higher GPD and ATPase
activities (independent of type) than control, probably reflecting the
larger proportion of dark ATPase fibers in these cats. These observations
indicate that 6 mo after spinalization in adult cats, some of the fibers of
a fast muscle became "faster" and developed oxidative and glycolytic enzyme
profiles that normally are exhibited in fast fatigable motor
units.(ABSTRACT TRUNCATED AT 250 WORDS)
