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At least 721 records · Page 40Linked to original sources
PubMed1978

Biochemical and morphometric studies of the relationship of acetylcholine synthesis and vesicle numbers after stimulation of frog neuromuscular junctions: the effect of a choline-O-acetyltransferase inhibitor.

The present study compares choline acetylase (ChAc) activity with morphometric determinations of synaptic vesicles at the neuromuscular junctions of frog pectoralis muscle subjected to high and low frequency stimulation in the presence or absence of NVP, a ChAc inhibitor. Muscles stimulated at 10/sec for 20 min with one hour rest, in the presence of NVP, showed an approximately 50% reduction in synthesis of Ach, and a 50--60% reduction in the numerical density of synaptic vesicles relative to controls preparations. Similar nerve muscle preparations stimulated at 2/sec for one hour without rest, in the presence of NVP, also showed approximately 50% less synthesis of Ach and vesicle numbers 43% lower than that seen in control muscles treated in the same way in the absence of drug. The results indicate a correlation between the inhibitory effect of NVP on ChAc and the numbers of vesicles present within terminals. In addition, stimulation of nerve terminals, with or without NVP, produced a significant increase in the numerical density of synaptic vesicles over respective unstimulated controls. These and other results are discussed in relation to current hypotheses concerning recirculation of synaptic vesicles.

Acetylcholine↗
PubMed1984

Immunochemical analysis of myosin heavy chains in the developing chicken heart.

Monoclonal antibodies (McAb) against myosin from the pectoralis muscle of the adult chicken have been generated and shown to react specifically with the myosin heavy chain (MHC). The reactivities of two such McAbs with myosin from adult chicken atrial and ventricular myocardium were further analysed by immunoautoradiography, radioimmunoassay, and immunofluorescence microscopy. Monoclonal antibody MF 20 was found to bind both atrial and ventricular MHC and stain all striated muscle cells of the adult chicken heart. In contrast, McAb B1 bound specifically to atrial myocytes in immunofluorescence studies, while immunoautoradiography and radioimmunoassay demonstrated the specificity of this antibody for the atrial MHC. Upon reacting these McAbs with myosin isolated from embryonic hearts where definitive atria and ventricles were present, the same specificity of antibody binding was observed. Immunofluorescence studies demonstrated that all striated muscle cells of the embryonic heart contained MHCs recognized by MF 20, while only atrial muscle cells were bound by B1. When extracts of presumptive atrial and ventricular tissue were reacted with MF 20 and B1, significant reactivity of MF 20 was first observed at stage 10 in the presumptive ventricle and thereafter this McAb reacted with all regions of the developing myocardium. Binding of B1 was detected approximately 1 day later at stage 15 and was confined to atrial-forming tissues. These data demonstrate antigenic similarity between adult and embryonic MHC isolated from atrial myocardium and suggest the expression of an atrial-specific MHC early in the regional differentiation of the heart.

Animals↗
PubMed1984

Age-dependent changes in myogenic precursor cell compartment sizes. Evidence for the existence of a stem cell.

Individual myogenic cells were isolated from the pectoralis muscles of chick embryos from days 8-14 of embryogenesis. When separately cloned, these cells produced three types of colonies in culture: (1) Positive: all cells in the clone were terminally differentiated muscle cells; (2) negative: no cells in the clone were terminally differentiated muscle; (3) mixed: some cells in the clone were terminally differentiated muscle. Positive clones from all ages tended to contain 2n cells (n = 0, 1, 2, 3, 4). Negative clones were found in all sizes and did not cluster around powers of 2 in cell number. Mixed clones were, by far, the most common type among those clones larger than 24 in cell number. Estimates of cell numbers in embryonic muscle tissue revealed that, while the numbers of cells in all myogenic compartments increased steadily with embryonic age, the number and percentage of precursor cells that produced large mixed clones increased dramatically. Subclones, prepared from populations of cells equivalent to large mixed clones, yielded both small positive and large mixed colonies. This indicated that the precursors to the large mixed clones were also precursors to the smaller positive clones. These observations suggest a model for the myogenic lineage in which there exists a stem cell that can generate, by a series of asymmetric divisions, cohorts of terminally differentiated muscle cells. The model can explain the asynchrony of production of terminally differentiated muscle cells both in vitro and in vivo.

Animals↗
PubMed1984

In vivo effects of three calcium blockers on chickens with inherited muscular dystrophy.

Genetically homozygous Line 413 dystrophic chickens were given in separate trials daily i.p. injections of aqueous solutions of the calcium blocker drugs, diltiazem, verapamil, or nifedipine. At a dosage of 20 mg/kg/day, drug therapy in each case significantly prolonged the functional ability of the dystrophic chickens as quantitated regularly by a standardized test for righting ability. Enhanced functional ability, however, was not generally accompanied by a decrease in the usually high plasma creatine kinase activity. In addition, there was no change in the pectoralis muscle mass or protein with any of the drug treatments. Moreover, no significant reduction in the abnormally high total muscle calcium was found with calcium blocker treatment. Also, there was no marked change in the histopathology of muscle from the drug-treated dystrophic chickens. We concluded that drugs with calcium entry blocker activity offer only limited benefit in retarding dystrophic symptoms expressed in the chicken (viz., short-term enhancement in righting ability).

Animals↗
PubMed1989

Circulating levels of insulin and avian pancreatic polypeptide in pigeons under different experimental conditions.

Changes in circulating levels of insulin and avian pancreatic polypeptide (APP) were studied in pigeons under different experimental conditions. Anesthetized pigeons in which the pectoralis muscles were stimulated electrically for periods of 1 or 5 hr showed significant reduction in plasma insulin levels but not in APP levels. Cold exposure (-15 degrees, 90 min) of fully feathered (FF) or partially (dorsum and breast) defeathered (PD) pigeons produced no significant changes in plasma levels of insulin or APP. Heat exposure (+45 degrees, 90 min) of FF and PD pigeons caused no change in plasma levels of insulin; however, APP levels were significantly increased. In pigeons subjected to bilateral cervical vagotomy, there was no change in the level of plasma insulin but APP levels were found to be significantly increased.

Animals↗
PubMed1994

Analysis of the kinematic and dynamic behavior of the shoulder mechanism.

A finite element musculoskeletal model of the shoulder mechanism consisting of the thorax, clavicula, scapula and humerus has been used for analysis of the kinematic and dynamic behavior. The model includes 16 muscles, three joints, three extracapsular ligaments and the motion constraints of the scapulothoracic gliding plane which turns the shoulder girdle into a closed-chain mechanism. Simulations are inverse dynamic. Input variables are the positions of the shoulder girdle and humerus which have been recorded in 10 subjects during unloaded and loaded humeral abduction and anteflexion. Comparisons of muscle force predictions and EMG recordings are hampered by the unknown force-length relationship and the length dependency of EMG amplitude. It is concluded that EMG amplitude cannot be used for validation of complex musculoskeletal models. Muscle function is analyzed with help of a force and moment balance of the three joints. The moment balance includes the contributions of ligaments and the reaction forces at the scapulothoracic gliding plane. The scapulothoracic gliding plane is very important for the motions and the stabilization of the shoulder girdle. The direction and magnitude of joint reaction forces are calculated as well. It is concluded that the model provides good insight into the mechanics of the shoulder mechanism and that it enables an analysis of the function of morphological structures.

Acromioclavicular Joint↗
PubMed1985

Analysis of the metal-induced conformational change in myosin with a monoclonal antibody to light chain two.

A monoclonal antibody capable of detecting a conformational change in myosin light chain two (LC2) was characterized in detail. The antibody was shown to bind only to myosin LC2 when tested against fast skeletal myosin (chicken pectoralis muscle). With cardiac or slow muscle myosins, the antibody exclusively recognized their first light chains (LC1). Staining of myofibrils by the monoclonal antibody could be observed only after their irreversible denaturation by acetone or ethanol, or after incubation of the myofibrils in divalent metal chelators. This latter effect was shown to be fully reversible. The metal effect was independent of ionic strength although the affinity of the antibody for myosin was depressed at high salt concentrations. Similar metal effects were detected in the binding of antibody to cardiac or slow myosins. Neither the metal nor the ionic strength-related inhibition of antibody binding were detected with denatured myosin. The antibody binding site overlaps one of the alpha-chymotryptic sites in LC2 protected by divalent metals. Electron microscopic observations of myosin-antibody complexes demonstrated that the antibody binding site is located near the head-rod junction of myosin. Since the binding site of this monoclonal antibody has been mapped by recombinant DNA methods to the junction of the first alpha-helical domain with the calcium binding site of LC2, the location of the calcium binding site must also be located near the head-tail junction of myosin. A model for conformational changes at the myosin head-tail junction is proposed to account for the metal-induced blockage of antibody binding and the inhibition of alpha-chymotryptic digestion of LC2.

Animals↗