TRANSIENT INVOLVEMENT OF GAP JUNCTIONAL C OMMUNICATION BEFORE FUSION OF NEWBORN RAT MYOBLASTS

Heptanol-sensitive gap junction communication was characterized by the gap-FRAP method (fluorescence recovery after photobleaching) in confl uent rat myoblasts developing in primary culture. Cell to cell dye dif fusion was mainly restricted to a short period of the prefusion lag pe riod and disappeared during fusion promotion except between some myobl asts and myotubes. This short period of occurrence of gap junction com munication might be transiently and partially involved during the firs t steps preparing the subsequent fusion, since treatment with an uncou pler (heptanol) reduced the formation of multinucleated myotubes. Duri ng subsequent steps, functional gap junctions are not involved between myoblasts in the process of fusing, but a possible secondary involvem ent for fusion of remaining myoblasts to newly-formed myotubes is disc ussed. These data, together with results from other authors, suggest a regulatory role of gap junction communication in development and fusi on of skeletal muscle cells, by providing a pathway for exchanging sma ll molecules from one myoblast to another.