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The present study aimed to determine the kinetics of l-3,4-dihydroxyphenylalanine (l-DOPA) uptake in an immortalised cell line of rat capillary cerebral endothelial cells (clones RBE 4 and RBE 4B), to define the type of inhibition produced by l-5-hydroxytryptophan (l-5-HTP), 2-aminobicyclo(2,2,1)-heptane-2-carboxylic acid (BHC) and N-(methylamino)-isobutyric acid (MeAlB) and its sodium dependence. Non-linear analysis of the saturation curves for l-DOPA and l-5-HTP revealed in RBE 4 cells K_m values (in μM) of 72 and 102 and in RBE 4B cells K_m values (in μM) of 60 and 118, respectively. IC₅₀ values for l-5-HTP (RBE 4, 1026 μM; RBE 4B, 831 μM) obtained in the presence of a nearly saturating (250 μM) concentration of l-DOPA were almost 5-fold those obtained when non-saturating (25 μM) concentrations of l-DOPA were used. IC₅₀ values for BHC obtained in the presence of a nearly saturating (250 μM …