Cell density- and membrane region-dependent mobility of anionic residue-containing molecules in 3T3 and transformed...

Mobility of anionic residue-containing molecules on 3T3 and simian virus 40-transformed 3T3 (SV40-3T3) cell surfaces was ultrastructurally examined using polycationic ferritin (CF) particles in vitro. CF-binding experiments at 4 degrees C showed continuous distribution of CF particles on entire surfaces of both cells. When 3T3 cells were incubated with CF at 37 degrees C, cell membrane-bound CF particles were rearranged to form clusters in sparse cultures. Almost all CFs on the ventral cell surface were present in clusters. Clustering rate and size were smaller on the dorso-lateral surface in high cell density than on the same region in low density. On the ventral in high density, CFs distributed in clusters or singly at broader zone than in sparse cultures. In the case of sparse cultures on dishes from which confluent 3T3 cells had been removed, the CF distribution pattern was similar to that in high density. On the other hand, its density-dependent change was hardly found in both surfaces of transformed counterparts. The clustering was remarkable on all cell surface areas and tended to differ regionally. The distribution pattern was similar to those in sparse 3T3 cell cultures. These results show cell density-, membrane region- and extracellular matrix-dependent mobility of anionic residue-containing molecules on the 3T3 cell membrane, and remarkably high, a little region-dependent, and density- and matrix-independent mobility in SV40-3T3 cells, suggesting relation of the mobility to cell-cell communication.