Quantitative ultrastructure of histochemically identified avian skeletal muscle fiber types (original) (raw)
1987, The anatomical record
A cryostat retrieval method and combined adenosine triphosphatase (ATPase) and acetylcholinesterase (AChase) method were used to study the ultrastructure and innervation of histochemically identified skeletal muscle fibers in different pigeon muscles. The Z-line structure and volume percentage sarcotubular system were analyzed from different muscles selected for their composition by fiber type. Histochemically, three main fiber types were investigated: slow tonic fibers with a moderate ATPase activity after preincubation at acid or alkaline pH; fast-twitch fibers that had high activity after alkaline treatment and low activity after acid preincubation; and a type considered to be slow-twitch that had low activity after alkaline, and high after acid preincubation. Both the slow tonic and slow-twitch fibers had multiple, en grappe innervation, while the fast-twitch fibers had robust, single end plates. The Z-line of the fast-twitch and slow-twitch fibers had a regular square lattice pattern, in contrast to the granular, nonlattice structure of the slow tonic Z-line. The volume percentage sarcotubular system of the slow-twitch fibers was intermediate between and significantly different from that of the fasttwitch and slow tonic fibers. These correlative analyses suggest that the avian muscles contain not only the fast-twitch and slow tonic fibers previously known, but also a slow-twitch fiber that appears to be intermediate between the tonic and the mammalian slow-twitch fiber type. Based on the abundance of the sarcotubular system, this fiber type appears to be fast-contracting and-relaxing, in spite of being multiply innervated. The characterization of skeletal muscle fiber types is important for clinical, functional, and developmental studies because there may be fiber type specificity of the muscles' reactions to various experimental, ontogenetic, and pathologic changes. It is clear that a variety of
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The Journal of physiology, 1987
1. Normal and chronically stimulated peroneus longus muscles of the cat's hind limb were studied with respect to fibre size and staining properties for myofibrillar (myosin) adenosine triphosphatase (ATPase) and succinate dehydrogenase (SDH) activity. The intensity of staining for SDH activity was measured by microphotometry from the central portions of the muscle fibres ('core-SDH staining'). For comparison, histochemical properties were also studied in non-stimulated soleus muscles. 2. On account of the pH sensitivity of their myofibrillar ATPase, about 18% of the fibres in normal peroneus longus muscles were classified as type I, and about half of the remainder as II A and II B respectively. 3. In the normal peroneus longus muscles, the mean diameter of single muscle fibres generally varied between about 25 and 75 micron, whereby the average size of type I less than type II. 4. In the normal peroneus longus muscles the staining intensity for core SDH varied over a wid...
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