Hypoxia induces different responses of striatal high- and low- affinity dopamine uptake sites

The dopamine (DA) uptake over a concentration range from 0.03 to 100 microM was studied in S1 fractions of the rat striatum prepared from control rats and those exposed for 14 h to hypobaric hypoxia. The uptake exhibited non-Michaelis-Menten kinetics, which were evaluated by applying an equation assuming two transport sites. The high-affinity uptake site was characterized by an apparent Michaelis-Menten constant of 0.47 microM and an apparent maximal transport rate of 113 pmol/mg protein/30 s. The respective constants of the low-affinity uptake site were 52.8 microM and 1490 pmol/mg protein/30 s. One hour after hypoxia kinetic constants of the high-affinity uptake were unchanged but the maximal transport rate of the low-affinity uptake was increased by 50%. The elevated low-affinity uptake capacity may represent a means of adaptation to hypoxia allowing a faster removal of high extracellular concentrations of DA.