C.R. Ashmore

Some observations on the innervation patterns of different fiber types of chick muscle.

Abstract Muscle fibers from the tonic anterior latissimus dorsi and the phasic sartorius and complexus muscles of chicks were examined for their terminal innervation patterns. Advantage was taken of a recently developed cytochemical technique which allows simultaneous visualization of muscle fiber types and their end plates. This technique increases the sensitivity of the acetycholinesterase assay. It was found that both fiber types in the anterior latissimus dorsi as well as the β fiber in the phasic muscles have similar patterns of innervation. All are multiply innervated with major end plates spaced at regular intervals. In addition, many minor end plates are randomly scattered along these fiber types. Despite similar innervation patterns, all three types of fibers exhibit different myofibrillar adenosine triphosphatase characteristics.

Simultaneous cytochemical demonstration of muscle fiber types and acetylcholinesterase in muscle fibers of dystrophic chickens.

Abstract A cytochemical procedure is described which allows the simultaneous observation of different types of muscle fibers and their motor end plates. The procedure utilizes an assay for myofibrillar adenosine 5′-triphosphatase (ATPase) activity followed by an assay for acetylcholinesterase (AChE) activity. This combined assay eliminates the necessity for using serial sections for observation of these two parameters. This combined assay increases the apparent AChE activity such that sites of AChE activity are revealed which are not visualized when using the AChE assay alone. In muscles from chicks with hereditary muscular dystrophy, it is shown that initially dystrophic fibers contain nuclei which react strongly for AChE activity. Subsequently many fibers exhibit an intense reaction for AChE activity over a major portion of their cell surface. AChE activity is also found along the splits of fragmenting fibers and on the periphery of necrotic vacuoles.

Transplantation of the anterior latissimus dorsi muscle in normal and dystrophic chickens

Abstract The anterior latissimus dorsi, a slow-tonic muscle, and the posterior latissimus dorsi, a fast-twitch muscle, were auto-transplanted to the site of the biceps brachii, a fast-twitch muscle. The regenerate muscle contained only α (fast-twitch) fibers when the posterior latissimus dorsi was the donor muscle. The regenerate contained both α and β (slow-twitch) fibers when the anterior latissimus dorsi was the donor muscle. No differences were observed between regenerates in normal and dystrophic chicks.

Proteolytic enzyme activities and onset of muscular dystrophy in the chick

The relationship between proteolytic enzyme activities, soluble protein profiles, and progression of pathology in dystrophic chick muscle was investigated. Activities of cathepsins C and H, and calcium-activated protease were significantly higher in dystrophic patagialis and pectoralis muscles compared with normal muscles prior to the onset of extensive muscle fiber necrosis. Proteolytic enzyme activity of dystrophic muscle remained constant relative to normal muscle during development while muscle pathology progressed in both patagialis and pectoralis muscles. There were more protein bands (60-80 kDa) in the dystrophic muscle extracts compared with normal at all ages studied. Activities of calcium-activated protease in the dystrophic pectoralis and patagialis were similar although muscle pathology progressed much more rapidly in the dystrophic pectoralis. We conclude there is no causal relationship between the activity of the above proteolytic enzymes and the development of muscle fiber necrosis. The elevated activities of proteolytic enzymes in dystrophic muscle may be due to abnormally accelerated growth.

Comparative aspects of mitochondria isolated from αW, αR, and βR muscle fibers of the chick

Abstract Muscles from the chick, composed primarily of αR, βR, or αW fibers, were compared with regard to whole muscle succinic dehydrogenase (SDH) activity, mitochondrial protein yield, mitochondrial SDH activity, and the ability of isolated mitochondria to oxidize α-glycerol phosphate and β-hydroxybutyrate. Total SDH activity is higher in αR than in βR fibers due primarily to higher specific activity of mitochondrial SDH rather than more mitochondria. Neither type of red fiber can oxidize α-glycerol phosphate, whereas αW fibers exhibit coupled oxidation with this substrate. Apparently this capacity is acquired during transformation of αR to αW fibers. The capacity to perform coupled oxidation with β-hydroxy-butyrate is limited to βR fibers. It is concluded that αR and βR fibers are fundamentally different from each other, and that studies utilizing “red” muscles must account for variable proportions of αR and βR fibers.

Effects of stretch and denervation on protease activities of normal and dystrophic chicken muscle

Changes of protease activities that follow passive stretch, denervation, and denervation plus stretch were followed in the patagialis muscle of normal and dystrophic chicks between 6 and 7 weeks of age. The baseline activities of cathepsin C, cathepsin D, and leucine aminopeptidase in dystrophic muscle were 2 to 3.5 times higher than in normal muscle. Passive stretch and denervation induced increases in protease activities by 40 to 120% in normal muscle, whereas the same treatments did not significantly affect the activities of the enzymes in dystrophic muscle. We conclude that the level of protease activity in dystrophic chicken muscle at 6 weeks of age had already attained a maximum limit and could not be increased even by denervation. In spite of protease activities, which were not different from control dystrophic muscle, denervated dystrophic muscles lost muscle weight rapidly whether they were stretched or not. They weighed 60% less than the innervated control muscle after 7 days. Inherently high protease activities in dystrophic muscle do not vary at this age regardless of whether or not the muscle is gaining or losing weight.