Transient involvement of gap junctional communication before fusion of newborn rat myoblasts

Heptanol-sensitive gap junction communication was characterized by the gap-FRAP method (fluorescence recovery after photobleaching) in confluent rat myoblasts developing in primary culture. Cell to cell dye diffusion was mainly restricted to a short period of the prefusion lag period and disappeared during fusion promotion except between some myoblasts and myotubes. This short period of occurrence of gap junction communication might be transiently and partially involved during the first steps preparing the subsequent fusion, since treatment with an uncoupler (heptanol) reduced the formation of multinucleated myotubes. During subsequent steps, functional gap junctions are not involved between myoblasts in the process of fusing, but a possible secondary involvement for fusion of remaining myoblasts to newly-formed myotubes is discussed. These data, together with results from other authors, suggest a regulatory role of gap junction communication in development and fusion of skeletal muscle cells, by providing a pathway for exchanging small molecules from one myoblast to another.