Concanavalin A inhibits fusion of myoblasts and appearance of acetylcholine receptors in muscle cultures

Studies on the effect of glycoprotein processing inhibitors on fusion of L6 myoblast cell lines

The effect of oligosaccharide processing inhibitors on the fusion of L6 myoblasts was studied. The glucosidase inhibitors, castanospermine, 1-deoxynojirimycin and N-methyl-deoxynojirimycin were potent inhibitors of myoblast fusion, as was the mannosidase II inhibitor, swainsonine. Inhibition of fusion was reversed when inhibitors were removed. However, the mannosidase I inhibitor, 1-deoxymannojirimycin did not inhibit fusion. Changes in cell membrane oligosaccharide structure were followed by monitoring the binding of concanavalin A (conA) and wheat germ agglutinin (WGA) to cell surface membranes in cells treated with processing inhibitors. All the processing inhibitors resulted in increased binding of conA and decreased binding of WGA; this is consistent with the known mechanisms of inhibition of the inhibitors used in the study. Inhibition of fusion by the processing inhibitors also resulted in reduced activities of creatine phosphokinase, an enzyme used as a marker for biochemical differentiation during fusion. Treatment of a non-differentiating conA-resistant cell line with processing inhibitors did not induce fusion, but the cells did show altered lectin-binding properties. The main conclusion drawn from these studies is that cell surface glycoproteins probably containing the mannose (Man)9 structure are important for the fusion reaction.

Dependence of Na+,K+-ATPase and electrogenic component of Em in cultured myotubes on cell fusion

This study was undertaken in order to determine the relation among cell fusion, [3H]ouabain binding and the membrane potential (Em) of cultured rat skeletal muscle. The amount of ouabain bound and the Em both increased with age, the increases being most dramatic following fusion. Inhibition of fusion prevented the developmental increases in both properties of cultured muscle. After fusion, the size of the electrogenic component of Em, determined by the decrease in Em produced by ouabain within 5-10 min, increased independent of the age at which fusion occurred. It is concluded that the increase in Em with age depends on postfusion appearance and activity of Na,K-ATPase.

The fusion of myoblasts

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Multiple controls for the synthesis of muscle-specific proteins in BC3H1 cells

The regulation of the synthesis of muscle-specific proteins has been examined in BC3H1 cells, a smooth muscle-like cell line isolated by Schubert et al. (J. Cell Biol., 1974, 61: 398-413.). The synthesis of both creatine kinase and the acetylcholine receptor appear to be under dual control, a positive control due to cell-cell contact which increases the rate of synthesis of this protein, and a negative signal, elicited by serum components, that decreases the rate of synthesis of these proteins. Induction of muscle-specific proteins in BC3H1 cells is a reversible process and can be arrested after partial induction has taken place by the addition of serum or high-molecular-weight protein fraction from serum to these cells. The high-molecular-weight protein fraction from serum is not by itself mitogenic for Bc3H1 cells and cannot be replaced by a variety of known hormones (mitogenic factors).