Changes of energy metabolism, myosin light chain composition, lactate dehydrogenase isozyme pattern and fibre type distribution of denervated fast-twitch muscle from rabbit after low frequency stimulation

Chronic electrostimulation after nerve repair by self-anastomosis: effects on the size, the mechanical, histochemical and biochemical muscle properties

This study tests the effects of chronic electrostimulation on denervated/reinnervated skeletal muscle in producing an optimal restoration of size and mechanical and histochemical properties. We compared tibialis anterior muscles in four groups of rats: in unoperated control (C) and 10 weeks following nerve lesion with suture (LS) in the absence of electrostimulation and in the presence of muscle stimulation with either a monophasic rectangular current (LSEm) or a biphasic modulated current (LSEb). The main results were (1) muscle atrophy was reduced in LSEm (-26%) while it was absent in LSEb groups (-8%); (2) the peak twitch amplitude decreased in LS and LSEm but not in LSEb groups, whereas the contraction time was shorter; (3) muscle reinnervation was associated with the emergence of type IIC fibers and proportions of types I, IIA and IIB fibers recovered in the superficial portion of LSEb muscles; (4) the ratio of oxidative to glycolytic activities decreased in the three groups with nerve injury and repair; however, this decrease was more accentuated in LSEm groups. We conclude that muscle electrostimulation following denervation and reinnervation tends to restore size and functional and histochemical properties during reinnervation better than is seen in unstimulated muscle.

Determination of muscle contractile properties: the importance of the nerve

Contractile phenotype of muscle fibres is strongly influenced by hormones, stretch and influences from the motor neurones, although cell lineage probably also plays a role. Motor neurones can affect muscle fibres by releasing neurotrophic substances and by evoking electrical activity in the muscle. For regulating contractile properties such as speed, strength and endurance it has been demonstrated that electrical activity is crucial, while the role of putative neurotrophic substances remains unclear. The signal to change is coded in the pattern of electrical activity. Thus, high amounts of activity lead to slow shortening velocity and myosin heavy chains, while low amounts of activity lead to a fast phenotype. For regulation of twitch duration frequency also plays a role, and for preventing atrophy in denervated muscles high frequency seems to be beneficial, particularly in fast muscles. Little is known about the excitation-adaptation pathway linking action potentials to expression of genes that are relevant for contractile properties. Muscle specific transcription factors of the helix-loop-helix family such as myoD and myogenin could be important for regulating genes related to metabolic profile and fibre size/strength, while their role in determining myosin heavy chain expression and classical fibre type is more uncertain.

Electrical stimulation of denervated muscle: is it worthwhile?

Research conducted over the past 25 years has demonstrated that muscle activity, not neurotrophic substances, is the most important factor in the regulation of specific physiological and biochemical properties of muscle fibers. Application of this knowledge has led to considerable experimentation with chronic electrical stimulation as a possible clinical tool for the treatment of denervated muscles. Evidence accumulated from animal studies has indicated that direct electrical stimulation of denervated muscles can to a large extent substitute for innervation and preserve or restore the normal properties of the muscles. Appropriate stimulation parameters were critical for a successful intervention, and the best results were obtained when the stimulation pattern resembled the firing pattern of the normal motoneuron. Thus, fast muscles required intermittent, brief, high frequency stimulation and slow muscles needed continuous, low frequency stimulation. For human denervated muscles, critical questions still remain to be resolved before electrical stimulation will yield the optimum benefit. Research must be performed in human subjects to define the appropriate stimulation parameters the stimulation current, and the type and placement of electrodes.

Fast-to-slow muscle conversion by chronic electrostimulation: effects on mitochondrial respiratory chain function with possible implications for the gracilis neosphincter procedure

The effects of chronic, around the clock, low-frequency electrostimulation on the respiratory chain activity and cytochrome content of freshly isolated mitochondria were evaluated in rabbit skeletal muscle before and after 30 days of continuous or cyclical electrostimulation using a totally implantable system and a training programme now used in humans. The respiratory activity measured in state III increased strongly after electrostimulation. The efficiency of the respiratory chain increased significantly after electrostimulation but the activity of complex [(reduced nicotinamide adenine dinucleotide dehydrogenase) did not increase. The amount of cytochromes a and a3, b562, and c and c1 increased clearly after electrostimulation. The respiratory activity rate of mitochondria obtained after continuous electrostimulation was apparently higher than after cyclical electrostimulation. Chronic uninterrupted low-frequency electrostimulation, using a clinical training programme, induces an increase in mitochondrial respiratory chain activity in purified mitochondria of skeletal muscle. These changes are the basis of induced resistance to fatigue in fast-to-slow muscle conversion by chronic electrostimulation.

Effects of intermittent high frequency electrical stimulation on denervated EDL muscle of rabbit

This study was performed to determine whether electrical stimulation can retard denervation-induced changes. The denervated extensor digitorum longus of the rabbit, a fast-twitch muscle, was stimulated at a rate mimicking its motoneuron firing pattern. The 100-Hz stimulation given intermittently subjected the muscle to a low mean total daily frequency of 1.6 Hz. Four weeks of stimulation resulted in no effect upon the denervated stimulated muscle. This stimulation protocol, therefore, is unable to substitute for the lost neuronal influence of the nerve. The muscle contralateral to the stimulated side showed physiological changes making it unsuitable to serve as a control.

Effects of long-impulse electrical stimulation on atrophy and fibre type composition of chronically denervated fast rabbit muscle

The efficacy of electrical stimulation on a chronically denervated muscle depends on stimulus parameters, which have an important influence on the development of atrophy. Stimulus frequency and/or total activity are particularly responsible for the development of some histological, biochemical and contractile features. The present study in 18 rabbits deals with a recently developed electrical stimulus, which had proved effective in maintaining muscle force following denervation. This current has (1) unusual long bidirectional rectangular impulses (20 ms) and (2) a frequency of 25 Hz, which is between the frequencies of fast- and slow-firing motor units. Electrical stimulation began 28 (in one animal 53) days after total motor and sensory denervation of the right hindleg, and was continued until the end of the experiment, up to 205 days. To mimic a therapeutic regimen, which should be agreeable to patients, daily treatment times were kept to a minimum (2 x 6 min), and surface electrodes were used. Morphometric evaluation of the fast flexor digitorum sublimis muscle showed that such electrical stimulation was able to preserve fibre diameter at a level of 72-86% of the initial values for several months, while unstimulated fibres showed the usual atrophy with a decrease of diameters below 40% of normal. The stimulation induced a "hybrid" fibre type with properties of a slow muscle (rich in mitochondria in NADH-dependent tetrazolium reductase staining and electron microscopy) as well as of a fast-twitch muscle (fibre type IIb in myofibrillar ATPase stainings).

Fibre types, calcium-sequestering proteins and metabolic enzymes in denervated and chronically stimulated muscles of the rat

1. Fibre types, Ca2+-sequestering proteins (parvalbumin, sarcoplasmic reticulum Ca2+-ATPase), enzyme activities of energy metabolism, and lactate dehydrogenase isozymes were studied in extensor digitorum longus (EDL) and soleus muscles of adult rats after denervation and direct stimulation for 45-61 days. The stimulation resembled the firing patterns of normal motor units (Hennig & Lømo, 1985) in either soleus (20 Hz, high amount) or EDL (150 Hz, low and high amount). 2. Low- and high-amount 150 Hz stimulation maintained essentially normal properties in the denervated EDL and induced many EDL-like properties in the denervated soleus, e.g. pronounced increases in Ca2+-ATPase and parvalbumin contents, a rise in the glycolytic enzyme activities, as well as a reversal of the lactate dehydrogenase H/M subunit ratio. The 150 Hz high-amount stimulation was not as efficient as the 150 Hz low amount in maintaining the fast properties of denervated EDL with the exception of the enzymes of aerobic oxidative metabolism. High-amount 20 Hz stimulation maintained essentially normal properties in the soleus but induced only moderate slow muscle characteristics in the EDL. 3. The maintenance of essentially normal properties by 'native' and the changes induced by 'foreign' stimulus patterns in the absence of the nerve indicate that evoked muscle activity plays a major role in controlling the phenotypic expression of muscle properties. However, the different responses of the denervated fast- and slow-twitch muscles to identical stimulus patterns further suggest that rat EDL and soleus muscles contain intrinsically different muscle fibres.

Effects of low and high frequency patterns of stimulation on contractile properties, enzyme activities and myosin light chain accumulation in slow and fast denervated muscles of the chicken

The effects of denervation and direct stimulation in fast and slow latissimus dorsii muscles were investigated in chicken. In slow ALD muscle, denervation resulted in an incompleteness of the relaxation, a decrease in MDH and CPK activities and an increase in fast myosin light chains (MLC) accumulation. Direct stimulation at either fast or slow rhythm prevented the effects of denervation on relaxation and CPK activity but was ineffective on MDH activity and fast MLC accumulation. Moreover, direct stimulation of denervated ALD caused rhythm-dependent change in tetanic contraction. In fast PLD muscle, the main changes in muscle properties following denervation were a slowing down of the time course of the twitch and an incompleteness of the relaxation, a decrease in LDH and CPK activities and in LC3F accumulation. Stimulation at a high frequency partly prevented the effects of denervation and resulted in a large accumulation of LC3F, while a low frequency stimulation did not restore the twitch time to peak, increased MDH activity and induced synthesis of slow MLC. This study emphasizes the role of muscle activity and its pattern in some properties of slow and fast chicken muscles following denervation.