Cell-cell contact and growth regulation of pinocytosis in 3T3 cells.
In sub-confluent cultures of Balb/c-3T3 cells, pinocytosis rates were increased after exposure to specific growth factors (serum; platelet-derived growth factor, PDGF; epidermal growth factor, EGF). Conversely, as cells became growth-inhibited with increasing culture density, there was a corresponding decline in pinocytosis rate per cell. In order to test whether density-inhibition of pinocytosis was influenced either by the growth cycle or by cell contact independently of growth, cells were induced into a quiescent state at a range of subconfluent and confluent densities. Under such conditions, cell density did not significantly inhibit pinocytosis rate. When confluent quiescent cultures in 2.5% serum were exposed to 10% serum, the resulting round of DNA synthesis was accompanied by enhanced pinocytosis per cell, even though the cells were in contact with one another. Furthermore, in a SV40-viral transformed 3T3 cell line, both the growth fraction and the pinocytosis rate per cell remained unchanged over a wide range of culture densities. These studies indicate that density-dependent inhibition of pinocytosis in 3T3 cells appears to be secondary to growth-inhibition rather than to any direct physical effects of cell-cell contact.
D000818:Animals; D002455:Cell Division; D002472:Cell Transformation, Viral; D002999:Clone Cells / Q000502:physiology; D003260:Contact Inhibition; D004247:DNA / Q000096:biosynthesis; D006133:Growth Substances / Q000494:pharmacology; D051379:Mice; D010873:Pinocytosis / Q000187:drug effects; D013539:Simian virus 40
D006133:Growth Substances; D004247:DNA