Cesium ions delay membrane fusion of chick embryo myoblasts in vitro: a conductivity study

Cesium has a wide range of effects on biological systems. However, the effects of this ion on muscle differentiation are not known. We have recently demonstrated that there is a sharp decrease in the conductivity and permittivity of the membranes of chick embryo myoblasts at the time of fusion (Bonincontro, A., Cametti, C., Hausman, R.E., Indovina, P.L. and Santini, M.T. (1987) Biochim. Biophys. Acta 903, 89-95). Analysis of the conductivity dispersion data in the radiowave frequency range using a 'single-shell' model showed that individual myoblasts and unfused myoballs have significantly higher membrane conductivity and membrane permittivity than fused myoballs. We show here that the sharp fall in these membrane electrical parameters occurs at 60 h of culture and is indeed very abrupt, taking place within one hour. In addition, we also demonstrate that cesium ions delay the sharp decrease in both the conductivity and permittivity of myoblast membranes by about 30 h. We discuss the possible mechanisms by which cesium perturbs potassium transport across these membranes and how this perturbation may affect fusion itself.