Regulation of transport in mammalian cell culture.

The regulation of amino acid transport has been investigated in Balb/3T3 cells. Transport for neutral amino acids in animal tissues is carried out by two distinct systems. The transport activity of the A system (alanine preferring) is inhibited by high internal of substrate amino acids, a process termed trans-inhibition. In contrast, the L system transport activity is greatly stimulated by high internal levels of substrate, a phenomenon termed trans-stimulation. Regulation of amino acid transport in animal cells occurs by a repression-derepression mechanism or by a feedback inhibition or feedback stimulation process. The level of endogenous amino acids is shown to be important in the regulation of transport activity. Cells which are slow growing or quiescent have increased levels of endogenous amino acids, which in turn effect the transport activity. The A system transport activity is decreased in quiescent cells, whereas L system transport activity increases. Conditions which effect endogenous amino acid levels have an effect on transport activity. Feedback regulation of transport activity through the amino acid pool levels is another way animal cells can regulate transport activity.