The kinetics of myoblast fusion

The kinetics of myoblast fusion were estimated using two complementary assays. Both utilized suspensions of fusion-competent cells, i.e. 48-52-h cultures of chick pectoral muscle grown in a low-calcium medium, thus minimizing contributions arising from cellular migration. One assay, designed to measure the onset of membrane contiguity, relies on the transfer of a lipid dye, diI-C18-[3], from labelled to unlabelled cells. The other assay, designed to estimate the kinetics of appearance of morphologically distinct multinucleate cells in suspension (myoballs), relies on enzymic dissociation of cellular aggregates followed by nuclear staining. The assays demonstrate significant membrane contiguity within 20-30 min after initiating the fusion process; however, the multinucleate myoball morphology does not appear for at least one additional hour.