Changes in albumin uptake during the lifespan of human fibroblasts in vitro.

It has been suggested that a deterioration of cell membrane functions in cell populations with a limited lifespan in vitro could explain the loss of division potential either through changes in permeability of in cell attachment. We analyzed membrane function measuring the uptake of iodinated human serum albumin (125ISA) at different passages during the lifespan in vitro of human adult lung fibroblasts. Monolayers were incubated with 100microng/ml 125ISA. One and sixty minutes later, cultures were washed and the cell bound radioactivity was determined; these values correspond respectively to adsorption and net uptake. Our results show a significant increased uptake of albumin by aging cells. The changes in cell permeability, however, are apparent only late during the life span. Old cultures were also more susceptible to the stimulatory action of polyornithine (PLO) on protein uptake. Results obtained with PLO on young cells showed that the cell takes up more albumin when there is membrane danage leading to leakage of proteins. These findings suggest that the increased uptake of albumin and the suceptibility to PLO are signs of membrane damage in cells that have reached the end of their lifespans. In that case, an increased protein uptake would be the prelude to cell death.