IS INTERCELLULAR COMMUNICATION VIA GAP-JUNCTIONS REQUIRED FOR MYOBLAST FUSION

Fusion of myoblasts to form syncitial muscle cells results from a comp lex series of sequential events including cell alignment, cell adhesio n and cell communication. The aim of the present investigation was to assess whether intercellular communication through gap junctions would be required for subsequent membrane fusion. The presence of the gap j unction protein connexin 43 at areas of contact between prefusing rat L6 myoblasts was established by immunofluorescent staining. These myob lasts were dye-coupled, as demonstrated by the use of the scrape-loadi ng/dye transfer technique. L6 myoblast dye coupling was reversibly blo cked by heptanol in short term experiments as well as after chronic tr eatment. After a single addition of 3.5 mM heptanol, gap junctions rem ained blocked for up to 8 hours, then this inhibitory effect decreased gradually, likely because the alcohol was evaporated. Changing heptan ol solutions every 8 hours during the time course of L6 differentiatio n resulted in a lasting drastic inhibition of myoblast fusion. We furt her investigated the effect of heptanol and of other uncoupling agents on the differentiation of primary cultures of embryonic chicken myobl asts. These cells are transiently coupled by gap junctions before myob last fusion and prolonged application of heptanol, octanol and 18-beta -glycyrrhetinic acid also inhibited their fusion. The effect of heptan ol and octanol was neither due to a cytotoxic effect nor to a modifica tion of cell proliferation. Moreover, heptanol treatment did not alter myoblast alignment and adhesion. Taken together these observations su ggest that intercellular communication might be a necessary step for m yoblast fusion.