The pattern of density dependent growth inhibition in murine fibroblasts

Observations on the pattern of nuclear incorporation of 3H-TdR in long term (8-day) and short term (3-day) 3T3 cultures with local cell densities between 0.2 times 10-4 and 6.2 times 10-4 cells/cm2 are reported. Contrary to a number of previous studies our observations indicate that density dependent inhibition is exhibited in relatively sparse cultures, commencing at 0.5 times 10-4 cells/cm2. Various possible mechanisms which could have caused the observed pattern of density-dependent regression in labelling index are discussed.