Freeze fracture ultrastructure studies have shown that contact inhibited 3T3 cells contain aggregated intramembranous particles (IMP) while transformed 3T3 cells have randomly distributed IMP. The results of this study show that the aggregation of IMP in 3T3 cells is primarily related to the degree of cell contact and not significantly affected by inhibition of cell movement. Cell cycle studies do, however, show a transient disaggregation of IMP during the mitotic phase of the cell cycle. These observations are interpreted to suggest that changes in membrane structure which occur during mitosis or following cell-to-cell contact may be associated with changes in membrane fluidity and the activity of membrane enzymes that appear to be critical for control of cell growth and cell division.
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This work is supported in part by USPHS grants number CA-13458 and contract CP-33357.