Effects of chronic electrical stimulation on contractile properties of long‐term denervated rat skeletal muscle.

Abstract

SUMMARY1. The contractile properties of fast-twitch (extensor digitorum longus or EDL) and slow-twitch (soleus) muscles in the rat were followed for periods of between 4 and 10 months after denervation. The effects of chronic electrical stimulation during the last 3-8 weeks of denervation were investigated.2. The fall in tetanic tension that follows axotomy ended after about 4 months' denervation. The equilibrium tension was about 0 75 % of control tension in EDL and 0 2-0{3 % in soleus.3. The low tension in soleus was due partly to the small diameter of the muscle fibres (atrophy) and partly to their necrosis that resulted in an 8-fold fall in specific tension (the force per unit cross-sectional area). Similar but less extreme changes occurred in EDL.4. It is speculated that the final level of tension reached by unstimulated denervated muscles is an equilibrium between decrease in force due to atrophy and necrosis and increase due to regeneration. Differences between the final tension levels in soleus and EDL cannot be accounted for quantitatively by known differences in atrophy alone. Therefore, the rate of necrosis in soleus and of regeneration in EDL may be higher.5. Chronic stimulation of long-term denervated muscle increased force generation by about 7-fold in EDL and between 20 and 55 times in soleus. The final tension reached was between 4 and 5 % of normal in both muscles. Specific tension of fibres was almost completely restored by stimulation and the number of fibres was normal. The failure to recover full tension was largely due to failure to reverse denervation atrophy completely.6. Twitch contraction and relaxation times were identical in denervatedstimulated soleus and EDL. There was no evidence for dependence on duration of stimulation or tension of the muscle. The normalized maximum rate of rise of tetanic tension remained higher in EDL than soleus. MIS 900144 I S. AL-AMOOD. D. M. LEW'IS AND H. SCHMALBRUCH

Atrophy, but not necrosis, in rabbit skeletal muscle denervated for periods up to one year

“…As a result of the changes during the first phase the muscle declines to 20 -30% of its original mass by 3-4 wk (5,8,25,44,52,60), and by 1-2 mo it develops only 25% of its original isometric tetanic tension (8,47). In the denervated rat EDL muscle, tetanic force is reported to decline even further over this period, to 1-3% of control values (1,14,30); at this stage mean fiber area is only 20 -30% of control (1,46), falling to 2.5% of control over subsequent months (1,13). In the rabbit TA muscle, we observed a decrease of ϳ50% in wet weight at 10 wk after denervation, with no further decline up to 51 wk.…”

“…The mass of the affected muscles falls rapidly within 5-7 days of axotomy (11,18,22,25,55,57,58) and declines further to 30 -50% of control weight in succeeding weeks (1,5,11,14,23,41,60). After several months, muscle weight stabilizes at ϳ5-20% of control (1,13,45).…”

“…The mass of the affected muscles falls rapidly within 5-7 days of axotomy (11,18,22,25,55,57,58) and declines further to 30 -50% of control weight in succeeding weeks (1,5,11,14,23,41,60). After several months, muscle weight stabilizes at ϳ5-20% of control (1,13,45).Within the muscles, individual fibers show a reduction of ϳ70% in cross-sectional area (CSA) over a period of months (5,14,21,37), and over 90% (1,21,45) in the longer term. Initially, fast (type II) fibers are more susceptible to atrophy than slow (type I) fibers (5,7,32,38,48,54,59), but over more prolonged periods the fiber types atrophy to a similar extent (6, 54).…”

“…Within the muscles, individual fibers show a reduction of ϳ70% in cross-sectional area (CSA) over a period of months (5,14,21,37), and over 90% (1,21,45) in the longer term. Initially, fast (type II) fibers are more susceptible to atrophy than slow (type I) fibers (5,7,32,38,48,54,59), but over more prolonged periods the fiber types atrophy to a similar extent (6, 54).…”

Risk factors for atherogenesis and cardiovascular autonomic function in persons with spinal cord injury

“…16 Electrical stimulation has been shown to improve muscle ®ber structure and function. 15,17,18 In animal models, investigators have reported the deleterious e ect of denervation on postreceptor insulin action, 19 exercise-induced glucose uptake, 20 insulin receptor binding, 21,22 receptor phosphorylation, 21 and the glucose transporter protein (GLUT-4). 23 ± 25 In a recent study, 26 individuals with tetraplegia were found to have a marked reduction in whole body glucose transport that appeared to be due to a proportional reduction in muscle mass.…”