concanavalin-a and Muscular-Diseases

Agonist-induced degeneration of locust muscle occurs only when desensitization of the excitatory glutamate receptors present on this tissue is inhibited. It has been suggested that an increase in intracellular Ca2+ is responsible for this degeneration. To test this proposal the accumulation of 45Ca by locusts muscle has been studied under various conditions, including those under which receptor desensitization was inhibited. Retractor unguis muscles from the metathoracic leg of locusts (Schistocerca gregaria) were used in these studies. All muscles exposed to L-glutamate exhibited an early increase in intracellular radioactivity but this was 2-3 times greater in muscle pretreated with concanavalin A (Con A) to block receptor desensitization. In the desensitizing system the increase in muscle radioactivity was not maintained, intracellular Ca2+-levels declining to control values after 30 min in 45Ca-saline-containing glutamate. In Con A-treated muscles intracellular Ca2+-levels plateaued well above control levels within 5 min of exposure to glutamate and were maintained at these levels throughout the period of glutamate treatment. These results support the contention that agonist-induced degeneration of locust muscle is triggered by entry of Ca2+ and a rise in intracellular concentration of this cation to a toxic level.

Topics: Animals; Calcium; Concanavalin A; Glutamates; Glutamic Acid; Grasshoppers; In Vitro Techniques; Ion Channels; Muscles; Muscular Diseases; Receptors, Cell Surface; Receptors, Glutamate

The binding characteristics of lectins with varying sugar specificities were investigated in muscle biopsies from normal individuals and from patients with neuromuscular disorders. Horseradish peroxidase (HRPA) and fluorescein isothiocyanate (FITC)-conjugated lectins were used for light microscopy and ferritin-conjugated Concanavalin A (Con A) for electron microscopy. In normal and diseased muscle a lectin specific for alpha-D-mannosyl residues (Con A) and a group of lectins specific for beta-D-galactosyl residues were found to bind to the perimysial and endomysial connective tissue, blood vessels and capillaries and clearly demonstrated the perimeter of each muscle fibre. Wheat germ agglutinin (WGA), specific for N-acetylglucosamine and N-acetyl-neuraminic acid residues, had a similar distribution of staining although it appeared to stain the capillaries more strongly. In contrast, lectins specific for alpha-L-fucose and N-acetyl-galactosamine did not stain specifically any structures in normal or diseased muscle. In biopsies from dystrophic patients Con A, WGA and the beta-D-galactose specific lectins were always associated with splits and in biopsies from a variety of disorders discontinuities in staining were observed at the periphery of occasional fibers. These were not found in normal muscle. Electron microscopy showed Con A bound to the basement membrane of muscle fibres and capillaries and the connective tissue. The plasma membranes themselves were unstained. These preliminary investigations of lectin binding in muscle have shown important differences in diseased muscle and demonstrate the application of lectin chemistry to the study of membrane structure.

Topics: Adolescent; Adult; Child; Child, Preschool; Concanavalin A; Female; Galactose; Histocytochemistry; Humans; Infant; Lectins; Male; Microscopy, Electron; Middle Aged; Muscular Diseases