Direct correlation of histochemical profile to the ultrastructure of single myofibers and their neuromuscular junctions from a mixed muscle

Abstract

It has been demonstrated that there are significant differences in the ultrastructural morphology of the three mammalian myofiber types and their neuromuscular junctions (NMJ). The description of these ultrastructural differences was based primarily on samples taken from muscles that were composed of predominantly one fiber type. The objectives of this study were 1) to determine if previously described ultrastructural characteristics could distinguish between the three fiber types and the NMJ in a mixed muscle containing similar percentages of each fiber type and 2) to determine if there were significant differences in the morphology of like fiber types when compared between two histochemical regions in a muscle with a compartmentalized fiber-type distribution. The muscle used in this study was the flexor carpi radialis (FCR) of the cat. The objectives were achieved by a direct correlation of ultrastructure to histochemical profile on the same isolated myofibers. This study revealed a wide range of morpohological variation among fiber types in the FCR. Although many fibers from the FCR could be classified by using accepted ultrastructural criteria, most could not. Compartmental differences were present in several of the ultrastructural parameters measured. The slow-twitch oxidative (SO) and fast-twitch oxidative-glycolytic (FOG) fibers in the oxidative compartment had a significantly larger myofiber core volume when compared to the fast-twitch glycolytic (FG) fibers from both compartments. Also, the FG fibers in the glycolytic region had a significantly larger membrane volume (terminal cisternae, T tubules, and sarcoplasmic reticulum) when compared to the FOG fibers in the oxidative compartment and the SO fibers in both regions.This study has demonstrated that considerable variation exists in the most commonly accepted ultrastructural features used for distinguishing the three myofiber types when sampled from a mixed muscle that is not dominated by one fiber type. These results suggest the possibility of a greater functional range in the same type of histochemically identified motor units from mixed muscle than in those from muscles containing predominantly one fiber type.Classifications of mammalian myofiber types have used a variety of criteria to distinguish among fiber types (e.g., histochemical profile, physiological properties, and morphology; see reviews by Close, 1972;

Mitochondrial morphometrics of histochemically identified human extraocular muscle fibers

“…Similar findings have been reported for animal (Eisenberg et al, 1974;Eisenberg and Kuda, 1976;Hoppeler et al, 1981;Galvas et al, 1982) and human (Cullen and Weightman, 1975;Jerusalem et al, 1975;Sjostriim et al, 1982;Staron et al, 1983Staron et al, , 1984 limb skeletal muscle. In two studies using the cryostat retrieval technique and mitochondrial morphometrics, type I human limb muscle fibers had the greatest mitochondrial volume fraction, IIb fibers the lowest, while IIa fibers were intermediate in value (Staron et al, 1983(Staron et al, , 1984.…”

Physiological role of skeletal muscle glycogen in starved mice

“…Hours of Starvation Phosphorylase a activity was higher and PAS reaction for glycogen decreased more markedly in type IIB fibers than in type IIA fibers after 2 and 4 days of starvation. Type IIA fibers contain numerous mitochondria (Eisenberg and Kuda, 1976;Galvas et al, 1982) and the pathway of the aerobic glycolysis (Jobsis and Duffield, 1967;Burke et al, 1973), whereas type IIB fibers have few mitochondria (Eisenberg and Kuda, 1975;Galvas et al, 1982) and the anaerobic glycolysis occurs in the fibers (Burke et al, 1973). In type IIB fibers, G6P produced via the glycogenolysis is converted into lactate by the anaerobic glycolysis (Conn and Stumpf, 1972;Burke et al, 1973).…”

Skeletal Muscle

“…Fast-red and slow-red fibres in rats, distinguished by an antibody against fast myosin, did not differ in electron micrographs (GAUTHIER 1979). GALVAS et al (1982) classified individual fibres of the cat flexor carpi radialis muscle using histochemistry and assessed the same fibres using electron micro:' scopy. GALVAS et al (1982) classified individual fibres of the cat flexor carpi radialis muscle using histochemistry and assessed the same fibres using electron micro:' scopy.…”