Dose-dependent effects of ionizing radiation on in vitro myoblast fusion

We have recently demonstrated by dielectric relaxation studies in the radio-frequency range that there is a sharp decrease in the conductivity and permittivity of the membranes of chick embryo myoblasts in vitro at the time of fusion (60 h) (Bonincontro et al. 1987). This sharp fall in membrane electrical parameters was subsequently shown to be due to changes in ionic flux, particularly of the Na+/K+ equilibrium (Santini et al. 1988). Ionizing radiation induces a wide variety of effects on biological membranes, including variations in membrane ionic transport. We wished to investigate if sublethal doses of gamma-irradiation could affect membrane electrical parameters and thus myoblast membrane fusion. Consequently, chick embryo myoblast aggregate cultures were irradiated with 3.25, 5.15 or 6.35 Gy at 24 h of culture. We found that the lower dose delays membrane fusion by about 10 h while the two higher doses block fusion up to 120 h of culture. Aggregates showed a very high cell viability. The possible mechanisms by which ionizing radiation causes these variations in myoblast membrane electrical properties and fusion are discussed.