Instantaneous force-velocity-length relationship in diaphragmatic sarcomere

Coirault, Catherine, Denis Chemla, Jean-Claude Pourny,Francine Lambert, and Yves Lecarpentier. Instantaneousforce-velocity-length relationship in diaphragmatic sarcomere.J. Appl. Physiol. 82(2): 404-412, 1997.The simultaneous analysis of muscle force, length, velocity, andtime has been shown to precisely characterize the mechanicalperformance of isolated striated muscle. We tested the hypothesis thatthe three-dimensional force-velocity-length relationship reflectsmechanical properties of sarcomeres. In hamster diaphragm strips,instantaneous sarcomere length (SL) and muscle length were simultaneously measured during afterloaded twitches. SL was measured by means of laser diffraction. Wealso studied the influence of initialSL, abrupt changes in total load, and2 × 10⁷ M dantrolene.Baseline resting SL at the apex of thelength-active tension curve was 2.2 ± 0.1 µm, whereasSL at peak shortening was 1.6 ± 0.1 µm in the preloaded twitch and 2.1 ± 0.1 µm in the "isometric" twitch. Over the whole load continuum and at anygiven level of isotonic load, there was a unique relationship between instantaneous sarcomere velocity and instantaneousSL. Part of this relationship was timeindependent and initial SL independent and was markedly downshifted after dantrolene. When five different muscle regions were considered, there were no significant variations ofSL and sarcomere kinetics along themuscle. These results indicate that the time- and initiallength-independent part of the instantaneous force-velocity-lengthrelationship previously described in muscle strips reflects intrinsicsarcomere mechanical properties.

     

Proteolytic activity of proteasome on myofibrillar structures

The physiologic function of proteasome remains unclear. Evidence suggests a role in degradation of ubiquitin-protein conjugates, MHC antigen presentation, and some specificity of substrate within certain cell types. To explore further the properties of proteasome we have examined its effect on a well defined structure, the myofibril. We find that despite its large size (20S) proteasome is able to degrade myofibrils and intact, permeabilized muscle fibrils. The proteins degraded showed some specificity because actin, myosin and desmin were degraded faster than -actinin, troponin T and tropomyosin. Changes in ultrastructure were slow and included a general loss of structure with Z and I bands effected before the M band and costameres.     

Molecular basis and PCR-DNA typing of the Fya/fyb blood group polymorphism

Spondyloepiphyseal dysplasia tarda (SEDL) is an X-linked recessive disorder characterized in affected males by short stature resulting from a growth defect of the vertebral bodies. We have extended our earlier studies by analyzing 15 families with newly identified microsatellite DNA markers; analysis of recombination events with these markers indicates that the gene responsible for SEDL is located in Xp22 between DXS 16 and DXS 987 on an interval spanning approximately 2 Mb.     

A cellulase/xylanase-negative mutant of Streptomyces lividans 1326 defective in cellobiose and xylobiose uptake is mutated in a gene encoding a protein homologous to ATP-binding proteins

Centre de Recherche en Microbiologie Appliquée, Institut Armand-Frappier, Université du Québec, Ville de Laval, Québec H7N 4Z3, Canada.     

Double helical arrangement of spread dinoflagellate chromosomes

Dinoflagellate chromosomes observed in thin section show regular patterns which have been shown to correspond to a liquid crystalline helicoidal arrangement of DNA. Peripheral DNA filaments form a system of loops in the surrounding nucleoplasm. When such chromosomes (studied in Prorocentrum micans) are in presence of water, they extend considerably and form a double helical bundle. At the periphery of these bundles, one observes numerous filaments, which are smooth and devoid of nucleosomes; their diameter is constant.This study, in phase contrast and in electron microscopy, allows statistical measurements. A geometrical model is proposed and shows the simplest way to pass from the intact to the extended form. The liquid crystalline character of the chromosome is probably involved in the extension mechanisms.     

Histone - induced changes in the cellular growth of synchronized chlamydomonas reinhardii are due to histone H1

The cellular growth ofChlamydomonas reinhardii is modified by the addition of a total exogenous histone fraction. These modifications may be related to chloroplast DNA replication; they are different according to the different classes of histones. The H₁ subfraction seems to be responsible for the effect of the total histone fraction.     

Cytology of various antennal setae in a troglobitic Mysidacea (Crustacea)

Summary The various antennal setae can be differentiated from each other by the number and the type of their dendrites and by the cuticular structure of their external parts; these features correspond to functional differences. Moreover, the work revealed differences in relation to the corresponding setae of a marine Mysidacea previously studied by Guse (1978). Various hypotheses linking the ultrastructural differences to those that characterize the environments in which these two species live can be put forward.Abbreviations A1, A3 simple setae A1, A3 - An antenna - B1, B2 setulate setae B1, B2 - Bi bifid seta - bp bending plane - c1, c2, c3 type 1, 2, or 3 cilia (outer dendritic segments) - cu cuticle - d1, d2, d3 type 1, 2, or 3 dendrites (inner dendritic segments) - ec enveloping cell - g Golgi apparatus - h helically arranged cuticle - md microtubule doublet - n nucleus - p apical pore - r ciliary root - s setules - sc scolopale - scc scolopale cell - Si sickle-shaped seta - sm small seta - st stopper - t extracellular matter tube     

Crystalline conformation of homo- and regular heteroglucan chains

Crystalline polysaccharides with 1 → 3−β and 1 → 4−β glycosidic linkages are the most prevalent ones in nature. An interpretation of recent X-ray data on 1 → 3−α glucan shows that it has a ribbon-like crystalline conformation similar to cellulose. Comparison of the crystalline conformation of the four principal homoglucans shows that they fall either in the ‘ribbon-like’ or ‘large amplitude’ helix class. Heteroglucans with a regular sequence of glucosidic linkages show characteristics of the ‘extended conformation’ rather than the ‘coiled conformation’ even when there is 50% of a linkage which in a homoglucan leads to a large amplitude helix. It is concluded that X-ray diffraction analysis fully establishes the hypothesis that the glycosidic linkage type is the determinant of polysaccharide conformation. In this respect, polysaccharides are more like synthetic polymers than proteins or nucleotides; in the latter, it is variation in the substituents which are responsible for the conformational diversity.     

Isolation and identification of some guanidino compounds in the urine of patients with hyperargininaemia by liquid chromatography,thin-layer chromatography and gas chromatography-mass spectrometry

Liquid column chromatographic studies of monosubstituted guanidino compounds, which are excreted in the urine of patients with hyperargininaemia are reported. The guanidino-positive peaks, with the highest excretion values, were isolated from urine and the isolated compounds were identified by thin-layer chromatography and gas chromatography—mass spectrometry. Guanidinoacetic acid, N-α-acetylarginine, argininic acid, γ-guanidinobutyric acid, arginine and α-keto-δ-guanidinovaleric acid were found to be excreted at high levels in the urine of patients with hyperargininaemia compared with controls.