PHORBOL ESTERS STIMULATE THE TRANSPORT OF ANIONIC AMINO-ACIDS IN CULTURED HUMAN FIBROBLASTS

The effect of phorbol esters on the transport of amino acids has been evaluated in cultured human fibroblasts. The activity of the Na+-dependent system XAG- for anionic amino acids is selectively and markedly stimulated by phorbol esters. The effect is maximal whithin 15 min; it is attributable to an increase in transport maximum (Vmax) and not prevented by inhibitors of protein synthesis. The half-maximal stimulation is observed at concentrations of phorbol 12,13-dibutyrate lower than 100 nM. Prolonged incubations in the presence of 1 μM phorbol 12,13-dibutyrate lower the binding of the ligand to its receptor with a loss of the stimulatory effect on transport. The results presented indicate that the stimulation of amino acid transport through system XAG- by phorbol esters requires the activation of protein kinase C. © 1990 Academic Press, Inc.