Properties of the lysosomal apparatus during differentiation of cultured striated muscle cells.

A technique for the preparation of relatively pure myoblasts from chick primary culture is described. Cultured rat myogenic cells (L6) were plated and grown to provide three morphologically distinct cell populations: perfusion, postfusion, and nonfusion. Homogenates of L6 cells demonstrated two major peaks of proteolytic activity at pH 3.0 and 5.5. The activity could be partially inhibited by leupeptin or pepstatin. Differential centrifugation indicated significant acid hydrolase activity in the "H" fraction of prefused cells, which shifted to the "L" fraction after fusion of the cells. Two populations of lysosomes were resolved in the myoblasts and myotubes after isopycnic centrifugation in Percoll. The equilibrium densities were 1.044 and 1.060-1.068. Cells were incubated with several protease inhibitors. Only chloroquine caused a large inhibition of protein degradation.