Amino acid uptake in growing and arrested human diploid cell populations.

Human diploid fibroblasts cultured in vitro weremonitored for amino acid uptake in preconfluent and confluent cultures under conditions amenable to growth and in confluent cultures arrested in an essentially nonmitotic state. Preconfluent and confluent cultures in growth medium showed similar uptake patterns for leucine and alpha-aminoisobutyrate; arrested cultures exhibited a reduced uptake of both amino acids. Kinetic measurements revealed a 4-fold reduction in apparent Vmax for alpha-aminoisobutyrate influx in arrested cultures. These results suggest that the culture conditions used in this study to produce restrictions in mitotic activity likewise influence amino acid accumulation.