Age-dependent decrease of growth responsiveness in density inhibited 3T3 cell populations and their interactions with SV 40-3T3 cells.

An aging process has been detected in stationary 3T3 cell cultures, especially in the presence of plasma-derived serum (PDS) from adult bulls. It leads to irreversible conversion of an increasing percentage of initially responsive cells of a stationary population into cells unresponsive to growth stimulation by newborn calf serum (NBCS) or reseeding at low cell density in the presence of NBCS. These unresponsive cells are viable in the sense that, following trypsinization, they reattach and spread on a new culture plate and can be maintained for many days. The conversion process is accelerated by increasing PDS concentration. It is antagonized by NBCS. It is accompanied by enhancement of growth-inhibiting interactions exerted by stationary 3T3 cell populations on SV 40-3T3 cells.