title: Neutral amino acid transport and in vitro aging.
abstract: Human fibroblasts possess five distinguishable systems for amino acid transport. Initial rates for three of these decline with in vitro age. The decline most noticeably affects the L system, whose rate for L-phenylalanine transport at 10 microM declines by 44% between the 27th and 39th population doubling levels. Accumulation of L-phenylalanine is similarly affected. The insensitivity of older cells to reduction of the amino acid concentration in culture medium casts doubt on possible interpretation of the transport decline as a causal factor in limiting growth.
mesh_terms: D000409:Alanine / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D000621:Aminoisobutyric Acids / Q000378:metabolism; D001692:Biological Transport; D002460:Cell Line; D002470:Cell Survival; D003470:Culture Media; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D006801:Humans; D007700:Kinetics; D010649:Phenylalanine / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013912:Threonine / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000621:Aminoisobutyric Acids; D003470:Culture Media; C100049:2-aminoisobutyric acid; D013912:Threonine; D012694:Serine; D010649:Phenylalanine; D000409:Alanine