Changes in myoblast membrane order during differentiation as measured by EPR.

The events which make possible the characteristic fusion of the cell membranes of embryonic myoblasts are known to involve modification of the cell membrane (Hausman, R.E., Dobi, E.T., Woodford, E.J., Petrides, S., Ernst, M. and Nichols E.B. (1986) Dev. Biol. 113, 40-48). Myoblasts from chick embryos were allowed to differentiate in gyrotory aggregate culture and the order of their membranes was measured by EPR. Two spin-labels which insert at different depths into the lipid bilayer were used. Measurement with the 5-nitroxystearate label showed an increase in myoblast membrane order (2T' parallel) from 0-15 h of culture and again from 26-38 h of culture. Measurement with the 12-nitroxystearate label showed the 0-15 h increase in order but the second increase was greatly reduced and shifted in time. While the specific sources of these changes in membrane order cannot yet be identified, the changes observed correlated well with known events of myogenic differentiation in vitro. The initial increase in membrane order occurred while the myoblasts were recovering from the effects of trypsin dissociation and undergoing gyrotory aggregation. The second increase in membrane order occurred during the known period of prostaglandin receptor activity and increased cell-cell adhesion.