Polymorphism of myofibrillar proteins of rabbit skeletal-muscle fibres. An electrophoretic study of single fibres.

Rabbit predominantly fast-twitch-fibre and predominantly slow-twitch-fibre skeletal muscles of the hind limbs, the psoas, the diaphragm and the masseter muscles were fibre-typed by one-dimensional polyacrylamide-gel electrophoresis of the myofibrillar proteins of chemically skinned single fibres. Investigation of the distribution of fast-twitch-fibre and slow-twitch-fibre isoforms of myosin light chains and the type of myosin heavy chains, based on peptide ''maps'' published in Cleveland. Fischer, Kirschner & Laemmli [(1977) J. Biol. Chem. 252, 1102-1106], allowed a classification of muscle fibres into four classes, corresponding to histochemical types I, IIA, IIB and IIC. Type I fibres with a pure slow-twitch-type of myosin were found to be characterized by a unique set of isoforms of troponins I, C and T, in agreement with the immunological data of Dhoot & Perry [(1979) Nature (London) 278, 714-718], by predominance of the beta-tropomyosin subunit and by the presence of a small amount of an additional tropomyosin subunit, apparently dissimilar from fast-twitch-fibre alpha-tropomyosin subunit. The myofibrillar composition of type IIB fast-twitch white fibres was the mirror image of that found for slow-twitch fibres in that the fast-twitch-fibre isoforms only of the troponin subunits were present and the alpha-tropomyosin subunit predominated. Type IIA fast-twitch red fibres showed a troponin subunit composition identical with that of type IIB fast-twitch white fibres. On the other hand, a unique type of myosin heavy chains was found to be associated with type IIA fibres. Furthermore, the myosin light-chain composition of these fibres was invariably characterized by a small amount of LC3F light chain and by a pattern that was either a pure fast-twitch-fibre light-chain pattern or a hybrid LC1F/LC2F/LC3F/LC1Sb light-chain pattern. By these criteria type IIA fibres could be distinguished from type IIC intermediate fibres, which showed coexistence of fast-twitch-fibre and slow-twitch-fibre forms of myosin light chains and of troponin subunits.     

Freeze-fracture studies of frog atrial fibres.

The freeze-fracturing technique was used to characterize the junctional devices involved in the electrical coupling of frog atrial fibres. These fibres are connected by a type of junction which can be interpreted as a morphological variant of the "gap junction" or "nexus". The most characteristic features are rows of 9-nm junctional particles forming single or anastomosed circular profiles on the inner membrane face, and corresponding pits on the outer membrane face. Very seldom aggregates consisting of few geometrically disposed 9-nm particles are found. The significance of the junctional structures in the atrial fibres is discussed, with respect to present knowledge about junctional features of gap junctions in various tissues, including embryonic ones.     

Controlled disassembly of peptide amphiphile fibres.

In this paper, the introduction of both a methionine residue and a nitrobenzyl derivative as a labile linker between the peptide part and the hydrophobic alkyl chain of a peptide amphiphile are presented. These modifications are shown not to inhibit the formation of structured assemblies that analogous peptide amphiphiles lacking the linkers are able to form. Moreover, the introduction of either labile linker allows removal of the peptide amphiphile's stabilizing hydrophobic moieties to initiate a controlled disassembly of fibre aggregates. This is achieved by either treatment with CNBr or UV irradiation, respectively. These disassembly mechanisms could be the starting point for methodology that allows further manipulation of self-assembled peptide amphiphile architectures.     

Hypertension after localized transection of brainstem fibres.

Transections in the brainstem of the rat just lateral to the nucleus tractus solitarii (NTS) caused severe hypertension. The results of this study suggest that the fibres involved are entering the NTS laterally and that deafferentation of the cells of this nucleus results in hypertension by removing an inhibitory central control.     

The pineal gland and Rosenthal fibres.

115 pineal glands, collected from patients who died from various neurologic and visceral diseases, were studied. The Rosenthal fibres (RF) forming gliosis is consistently evident in the subependymal tissue around the gland, in the pineal recessus and in the intrapineal glial proliferation. In several instances the focal gliosis exhibited a central cystic degeneration. The RF-forming gliosis of the pineal gland appears independent of the basic diseases and of the process of atrophy and degeneration of the gland parenchyma. The embryonic development of the pineal gland could explain why the formation of RF may be considered a quasi-physiologic process of this region.     

Structure of adenovirus fibre. II. Morphology of single fibres

Adenovirus type 2 fibres in crystals appear to be significantly longer than found previously (accompanying paper). We therefore examined isolated fibre by electron microscopy and measured a length of 370 A, consistent with the length found in the crystals. The specific N-terminal structure of the fibre caused a heterogeneity in the length that may at least partially explain the values of 280 to 310 A published previously. Green et al. described a 15 amino acid repeat in the primary structure of the shaft of the fibre thought to be associated with the specific three-dimensional folding of the shaft. We compared the adenovirus type 2 (with 22 repeats) and type 3 (with 6 repeats) fibre lengths and derived a contribution of 13.2 A to the length of the shaft per 15 amino acid repeat. Specific morphological features of the fibre are discussed in relation to its amino acid sequence.     

Exclusion of dextrans by meshworks of collagenous fibres.

Insoluble collagen from human dermis was equilibrated in a physiological medium with mixtures of 3H2O and fluorescein-conjugated dextrans of different molecular weights. Dextrans of mol.wts. greater than 10(5) were excluded from a volume of 3.82+/-0.87 ml(S.D.) per g of collagen; dextrans of lower molecular weight occupied a larger volume. The apparent excluded volume was proportional to the weight of the collagen. Dansylated albumin behaved similarly to dextran; the polymeric collagen from rat skin exhibited a much larger excluded volume than the insoluble collagen. These results indicated that the volume available to the plasma proteins in human dermis was limited by insoluble collagen as well as by the glycosaminoglycans of the tissue.     

Further studies on single fibres of bovine muscles.

Young & Davey (1981) (Biochem. J. 195, 317-327) identified numbers of polymorphs of myofibrillar proteins by sodium dodecyl sulphate/polyacrylamide gel electrophoresis of single muscle fibres isolated from three bovine muscles. Fibres were classed according to the distribution of polymorphs. The study has now been extended to eight diverse bovine muscles. The previous distinction made between fast and slow fibres is valid without exception in the extended study. Within these classes, variations in myofibrillar expression are examined within and between fibres, muscles and animals. Two slow muscles are contrasted; masseter is homogeneous in fibre type, whereas diaphragm is subtly heterogeneous, possibly arising from greater physiological demands. Of the myofibrillar polymorphs, attention is concentrated on two variants of fast-muscle myosin heavy chain. Both are present in all fast and mixed muscles examined, except sternomandibularis, and each is respectively associated with certain unidentified proteins. Within a muscle the fast-muscle myosin light-chain expression is the same irrespective of the heavy-chain variant. Histochemical techniques demonstrated that the variants are respectively associated with types IIA and IIB as defined by other investigators.     

Light diffraction study of single skeletal muscle fibres.

Light diffraction patterns from isolated frog semitendinosus muscle fibers were examined. When transilluminated by laser light, the muscle striations produce a diffraction pattern consisting of a series of lines that are projected as points onto an optical detector by a lens system. Diffraction data may be sequentially stored every 18 ms for later processing by digital computer systems. First- and second-order diffraction line intensities were examined from intact, chemically skinned, and glycerinated single fibers. The diffraction line intensities demonstrated a strong length dependence upon passive stretch from reference length to 3.6 micrometer. The first-order intensity linearly increased an average of 15-fold over the range examined. The magnitude of the second order intensity was less than the first order and showed an exponential rise with increasing length. Both first- and second-order intensities decreased upon muscle activation. Data from chemically skinned and glycerinated single fibers were not significantly different from intact fibers, indicating that the membrane structure has little effect upon the diffraction phenomenon in muscle. Theoretical model systems are examined in an attempt to find the basis of these results. Neither an analysis based on a diffraction grating with variable spacing nor the unit cell model of Fujime provides an explanation for the observed length dependency of intensity. Though the origin of the intensity decrease upon stimulation is not known, we have suggested that it could result from lateral misalignment of myofibrils and can occur upon activation.     

The chemical composition of bovine vitreous-humour collagen fibres.

The insoluble protein fraction was prepared from the central and posterior peripheral fraction of bovine vitreous humour. The collagen present in this fraction was solubilized by pepsin and fractionated by gel chromatography. Analysis of the solubilized collagen fractions showed that the alpha-chain component had an amino acid composition and yielded a series of CNBr-cleavage peptides that showed it was very similar to type II collagen obtained from articular cartilage. Bovine vitreous-humour collagen alpha-chains differed, however, from those of cartilage collagen in that they had a lower alanine content and differed in their susceptibility to cleavage by CNBr. Satisfactory cleavage was obtained after two CNBr treatments involving reduction and alkylation. In addition, significant quantities of other peptides constituents were present in the vitreous-humour collagen fractions, and the galactose and glucose content of the alpha-chain fraction was more than double that of the same fraction obtained from articular cartilage. Although the origin of the additional peptide constituents in the vitreous-humour collagen preparations is not known, the results obtained indicate that they are probably not derived from a distinct type of alpha-chain component but may be terminal peptides covalently linked to the alpha 1 type-II helical portions of the collagen. The differences in the chemical composition of the vitreous-humour collagen indicate that vitreous-humour fibres are composed of a special type-II collagen.     

A histoenzymatic study of rat intrafusal muscle fibres.

The histochemical activities of myofibrillar adenosine triphosphatase (ATPase), succinic dehydrogenase (SDH) and alpha glycerophosphate dehydrogenase (alpha-GPD) were studied in intrafusal muscle fibres of rat fast and slow muscles. The ATPase reaction was carried out after the three standard acid preincubations. The cold K2-EDTA preincubated ATPase reaction product was similar to that seen following the regular or alkali-preincubated ATPase reaction, except that the intermediate bag fibres exhibited much higher activity after cold K2-EDTA preincubation. Following either acetic acid solution or cold and room temperature K2-EDTA-preincubation, followed by the ATPase reaction, chain fibres of the fast muscles vastus lateralis and extensor digitorum longus exhibited a very low amount of reaction product as compared with those of the slow soleus. Veronal acetate and K2-EDTA preincubations (and equally preincubation in acetic acid solution) resulted in acid stable ATPase activity along the entire length of the typical bag fibres but only in the polar regions of the intermediate bag fibres. On the basis of differing alpha-GPD reaction, two sub populations of nuclear chain fibres were discovered in one spindle. It is a matter of conjecture, to what extent the histochemical differences of intrafusal fibres from fast and slow muscles reflects functional distinctions in the response to stretch of muscle spindles from fast and slow muscles.     

The staining of elastic fibres with Direct Blue 152. A general hypothesis for the staining of elastic fibres

Summary Elastic fibres may be stained by a number of dyes, e.g. Direct Blue 1 (C.I. 24410), Direct Blue 10 (C.I. 24340), Direct Blue 15 (C.I. 24400), Direct Blue 152 (C.I. 24366) and Direct Violet 37 (C.I. 24370). A convenient method using Direct Blue 152 has been developed which is specific for elastic fibres. The method is simple and allows the demonstration of other connective tissue fibres. Staining of elastic fibres is unimpaired by numerous blocking procedures or by changes in dyebath pH. These properties are shared by several standard elastic fibre stains.As the Direct dyes and several of the standard elastic fibre stains possess numerous aromatic rings a wide range of dyes containing varying numbers of aromatic rings were examined for ability to stain elastic fibres. No association was observed between the ability to stain elastic fibres and dye class, formal charge or the presence of hydrogen bonding groups. Staining was, however, definitely associated with the presence in the dye molecule of 5 or more aromatic rings. This suggested that van der Waals forces of attraction may be responsible for elastic fibre staining both by Direct dyes and the standard elastic fibre stains. Staining of elastic fibres as a side-effect in many procedures is similarly explicable.     

Hard fibres

These fibres, obtained from the leaves of agaves, Manila hemp, New Zealand flax and various bromeliads, are important in the manufacture of cordage and of coarse textiles.