Morphometric analysis of coated vesicles in developing rat muscle spindles.

The incidence of coated vesicles under sarcolemmal surfaces of equatorial, juxta-equatorial and polar regions in developing and adult spindles of the rat soleus muscle was examined by quantitative morphometry of transverse ultrathin sections. Coated vesicles were more numerous: 1) under primary sensory endings than under other types of neuromuscular contacts; 2) under the appositional sarcolemma between neighbouring intrafusal fibres than under free surfaces of the sarcolemma; and 3) in developing than in mature spindles. Factors such as location and age of the animal often interacted to produce an additive effect on the incidence of coated vesicles. Although there was a high incidence of coated vesicles at the postsynaptic surface under sensory terminals of bag2 fibres in 18 and 19 day gestational embryonic rats, it peaked in 4 day postnatal animals. The high incidence of coated vesicles at sensory endings supports the view that coated vesicles mediate neurotrophic interactions between afferents and intrafusal fibres during the critical late gestation and early postnatal time period, as sensory axons first contact their target fibres and exert a maximal directing influence on the differentiation of intrafusal fibre types. In addition, the preferential localization of coated vesicles under appositional rather than free surfaces of developing intrafusal fibres in 0-4 day rats suggests that they play a role in the transport of active substances among intrafusal fibres exhibiting different stages of maturity.     

Physiological and ultrastructural analysis of elongating mitotic spindles reactivated in vitro

We have developed a simple procedure for isolating mitotic spindles from the diatom Stephanopyxis turris and have shown that they undergo anaphase spindle elongation in vitro upon addition of ATP. The isolated central spindle is a barrel-shaped structure with a prominent zone of microtubule overlap. After ATP addition greater than 75% of the spindle population undergoes distinct structural rearrangements: the spindles on average are longer and the two half-spindles are separated by a distinct gap traversed by only a small number of microtubules, the phase-dense material in the overlap zone is gone, and the peripheral microtubule arrays have depolymerized. At the ultrastructural level, we examined serial cross-sections of spindles after 1-, 5-, and 10-min incubations in reactivation medium. Microtubule depolymerization distal to the poles is confirmed by the increased number of incomplete, i.e., c-microtubule profiles specifically located in the region of overlap. After 10 min we see areas of reduced microtubule number which correspond to the gaps seen in the light microscope and an overall reduction in the number of half-spindle microtubules to about one-third the original number. The changes in spindle structure are highly specific for ATP, are dose-dependent, and do not occur with nonhydrolyzable nucleotide analogues. Spindle elongation and gap formation are blocked by 10 microM vanadate, equimolar mixtures of ATP and AMPPNP, and by sulfhydryl reagents. This process is not affected by nocodazole, erythro-9-[3-(2-hydroxynonyl)]adenine, cytochalasin D, and phalloidin. In the presence of taxol, the extent of spindle elongation is increased; however, distinct gaps still form between the two half-spindles. These results show that the response of isolated spindles to ATP is a complex process consisting of several discrete steps including initiation events, spindle elongation mechanochemistry, controlled central spindle microtubule plus-end depolymerization, and loss of peripheral microtubules. They also show that the microtubule overlap zone is an important site of ATP action and suggest that spindle elongation in vitro is best explained by a mechanism of microtubule-microtubule sliding. Spindle elongation in vitro cannot be accounted for by cytoplasmic forces pulling on the poles or by microtubule polymerization.     

The amino-acid sequence of troponin C from frog skeletal muscle.

The primary structure of the troponin C from skeletal muscle of the frog Rana esculenta has been determined. The amino acid sequence was deduced from amino acid determinations of peptides obtained after cleavage with cyanogen bromide. Overlapping peptides were isolated from tryptic digests of performic-acid-oxidized troponin C and phthalylated performic-acid-oxidized troponin C. All overlaps have been determined except for the Arg-Ile sequence at position 103--104, which has been obtained by comparison with homologous troponins C. Frog troponin C consists of one polypeptide chain containing 152 amino acids. The calculated molecular weight is 18299. There is a single cysteine residue at position 101 and a single tyrosine residue at position 112. No histidine or tryptophan residues are present. The amino-terminal amino acid is N-acetylated. The homology of frog troponin C with other skeletal and cardiac troponin C is briefly discussed.     

Physiological polymorphism in a population of the common frog. I. The polymorphism of a population of the common frog for the trait of muscle tissue heat resistance]

A study was made of heat resistance (36+/-0.2 degrees C) of m. interphalangealis of the third finger of a hind extremity in animals of one population of Rana temporaria L. living on the boundary between Leningrad region and Pskov region. Within this population, the existence of three groups of individuals differing in heat resistance levels of their m. interphalangealis is postulated. This conclusion is based on the distribution curve of heat resistance values and on the application of the probit-method. The distribution of the frequency of occurrence of individuals in these three groups follows Hardy-Weinberg's equation.     

Characterization of a non-indexible equatorial x-ray reflection from frog sartorius muscle.

X-ray equatorial reflections from frog sartorius muscle were studied using a position sensitive detector. A weak reflection appeared between the 10 and 11 peaks which did not index on the hexagonal filament lattice. This reflection, first reported by Elliott et al. (1967), was further characterized. The spacing of the reflection varied in direct proportion to that of the 10 peaks for sarcomere lengths between 2·0 μm and 3·0 μm. Its intensity appeared relatively insensitive to length changes. Optical diffraction patterns from electron micrographs of oblique sections through muscle gave ratios for the spacings of the myosin filaments and the Z-disc lattice that correlated very closely with the X-ray results. It is suggested that the Z-disc structure is the major source of this nonindexible reflection.     

Muscle sound frequencies of the frog are modulated by skeletal muscle tension.

The purpose of this study was to determine the relationships among muscle sound frequencies, muscle tension, and stiffness. Time-frequency transformations of nonstationary acoustic signals provided measures of resonant frequency during isometric contractions of frog (Rana pipiens) semitendinosus and gastrocnemius muscles. A mathematical expression for muscle transverse resonant frequency, elastic modulus and tension, based on elastic beam theory, was formulated by the Rayleigh method adapted for muscles. For thin muscles, the elastic modulus was found to have negligible influence on transverse muscle resonant frequency. Changes in muscle tension were the major determinants of changes in transverse resonant frequency. Consequently, for thin muscles, the time course of muscle tension, but not elastic modulus, can be monitored acoustically during the early phase of contraction when muscles give rise to sounds. Muscles were found to be anisotropic with a modulus of elasticity, EL, measured via length perturbations near 0.1% muscle length peak-to-peak, that was much larger than the modulus of elasticity, Eb, that resists the lateral bending that causes sound production. The elastic and resonant behavior of a thin muscle is similar to a tensioned fibrous cable with distributed mass.     

Physiological polymorphism of a grass frog population. III. The effect of the season on the phenotypic manifestation of frog polymorphism by the level of muscle tissue thermostability]

A study was made of the phenotypical manifestation of physiological polymorphism of the population of the grass frog by the heat resistance level of m. interphalangealis in different seasons. In autumn (starting from the 2nd half of October), throughout winter, and in summer the polymorphism of frogs is well expressed, whereas in spring (during the reproduction period) and in the first half of October (during the migration of animals to the places of hibernation) the polymorphism appears to be hidden. The latter phenomenon is due to differences in the pattern of individual seasonal changes in the heart resistance of muscles in individuals of different groups.     

The blood supply of muscle spindles in some mammals and the pigeon.

The blood supply of muscle spindles was studied in serial cross sections in macaque, cat, rabbit, guinea pig, mouse and pigeon muscles which had been incubated in a medium containing 3,3' diaminobenzidine. Lumina of blood vessels were recognized by the reaction product that was localized within erythrocytes. The outer capsule was well vascularized, but few or no capillaries were seen in the periaxial space. The inner spindle capsule, which closely invests the axial bundle, was rarely contacted by periaxial capillaries at the equator and juxtequator. Capillaries occurred more frequently adjacent to intrafusal fibers at the polar region and beyond the end of the outer capsule. Shorter diffusion distances and, usually, higher capillary densities were found at the polar region than at the spindle midsection. This suggests that transcapillary exchange at the polar segment is nearer to conditions prevalent in extrafusal muscle than elsewhere in the spindle, provided the inner and outer capsules are not less permeable at the poles than at the midsection. Differences in blood supply among mammalian species appear to be related to receptor size.     

Physiological polymorphism of a population of the common frog. II. The polymorphism of the type of muscle tissue heat resistance in stress]

A study was made of the dynamics in the heat resistance of m. interphalangealis of individual grass frogs under stress. The response of muscle tissue to injury can be differentiated into three types according to the initial heat resistance level: increase, decrease and phase change of the resistance. The pattern of response of muscle tissue of individual frogs to stress is one of manifestationss of physiological polymorphism of the population.