Density regulation of amino acid transport in cultured, androgen-responsive tumour cells

Abstract

In androgen‐responsive cells, activity of a sodium‐dependent transport system for neutral amino acids is shown to be density‐dependent, whereas activity of a sodium‐independent system is not. Transport of the nonmetabolizable amino acid, α‐aminoisobutyric acid (α‐aib) was largely sodium‐dependent, whereas transport of cycloleucine (cyleu) was by both sodium‐dependent and sodium‐independent systems. The K_m for cyleu transport changed with density because only the sodium‐dependent portion of this transport was density‐dependent. By contrast, the V_max for α‐aib transport changed with density, indicating that either the amount of functional membrane carrier or the activity of the sodium pump was affected.