Structure of the cross-striated adductor muscle of the scallop

The structure of the cross-striated adductor muscle of the scallop has been studied by electron microscopy and X-ray diffraction using living relaxed, glycerol-extracted (rigor), fixed and dried muscles. The thick filaments are arranged in a hexagonal lattice whose size varies with sarcomere length so as to maintain a constant lattice volume. In the overlap region there are approximately 12 thin filaments about each thick filament and these are arranged in a partially disordered lattice similar to that found in other invertebrate muscles, giving a thin-to-thick filament ratio in this region of 6:1.The thin filaments, which contain actin and tropomyosin, are about 1 μm long and the actin subunits are arranged on a helix of pitch 2 × 38.5 nm. The thick filaments, which contain myosin and paramyosin, are about 1.76 μm long and have a backbone diameter of about 21 nm. We propose that these filaments have a core of paramyosin about 6 nm in diameter, around which the myosin molecules pack. In living relaxed muscle, the projecting myosin heads are symmetrically arranged. The data are consistent with a six-stranded helix, each strand having a pitch of 290 nm. The projections along the strands each correspond to the heads of one or two myosin molecules and occur at alternating intervals of 13 and 16 nm. In rigor muscle these projections move away from the backbone and attach to the thin filaments.In both living and dried muscle, alternate planes of thick filaments are staggered longitudinally relative to each other by about 7.2 nm. This gives rise to a body-centred orthorhombic lattice with a unit cell twice the volume of the basic filament lattice.     

Some observations on caffeine-induced contracture of barnacle muscle fibers

Isometric tension measurements carried out on uncannulated, intact barnacle muscle fibers show that the minimal concentration of caffeine which produces contracture is 2mM and that which produces maximal tension is 30mM. Pretreatment of barnacle fibers with 3mM-caffeine renders these fibers less sensitive to a second challege e.g. with 30mM-caffeine, the amplitude of the contractile response being time-dependent. Caffeine-treated fibers fail to relax completely. Isotonic tension measurements indicate that the residual tension caused by caffeine is dose-dependent. Significantly, the tension caused by caffeine is independent of the external Ca²⁺.     

Some observations on the intercalated disc of a rat cardiac muscle.

During the experimental investigations special attention was paid to the orthomorphology of the ultrastructure of cardiac muscle intercalated disc in a rat. The contact junction between the cellular membranes of adjacent cells and intercellular spaces are typical for the cardiac muscle intercalated disc. Attention was paid to the three zone system of the junctions, namely: 1. nexus (zonula occludens), 2. fascia adherens (zonula adherens) and 3. macula adherens (similar to the desmosome). Apart from this the cell membranes adjacent to the cells may form digital indentations. A single injection of adrenaline in a dose of 2.4 mg/kg causes sinuate widenings of the intercellular space, but only in the zone of the fascia adherens. The structure of the nexuses and maculae adherentes is unchanged during this time.     

Morphohistochemical characteristics of structures of the esophageal cross-striated muscle tissue]

On the bases of histochemical enzymatic studies and morphometric investigations, some differences were revealed between cross-striated esophageal muscular tissue and other skeletal muscles of mammals. A peculiar feature of the esophageal musculature is prevalence of unitypical fibres with small diameter and possessing high activity of oxidating enzymes. According to these signs, esophageal myons can be ascribed to the first type of muscular fibres. Simultaneously, a high activity of myofibrillar ATPh is revealed in them. Thus, according to histochemical indices, cross-striated esophageal muscular fibres of mammals are quick and slowly fatiqued fibres.