Gllcocorticoid inhibition of amino acid transport in rat hepatoma cells

Dexamethasone rapidly and reversibly inhibits the initial rate of transport of α-aminoisobutyric acid in rat hepatoma cells in tissue culture. Colcemid and cytochalasin B neither inhibit transport nor interfere with its inhibition by dexamethasone, arguing that microtubules and microfilaments are not involved in this hormonal effect. Continuous protein synthesis is required both for the dexamethasone inhibition of transport and for its reversal, although cycloheximide alone inhibits transport in control cells by less than 25%. A model for the dexamethasone inhibition of amino acid transport is presented suggesting that glucocorticoids either block the synthesis or enhance the degradation of a rate-limiting protein in the transport system.