Previous experiments reported that incubation of rat striatal synaptosomes with lactic acid (pH 5.5) resulted in an inhibition of dopamine (DA) uptake partially mediated by free radical damage. Since the DA uptake process is highly dependent on the functionality of Na+/K+-ATPase, the present study investigated whether this inhibition of DA uptake could be related to an alteration of the Na+/K+-ATPase activity. Striatal lactic acidosis was performed by direct addition of lactic acid in the incubation medium to obtain a pH as close as possible to that observed in ischemia. Acidosis (pH 5.5) induced a progressive decline in the specific DA uptake and a decrease of Na+/K+-ATPase activity in striatal synaptosomes. However, whereas loss of Na+/K+-ATPase activity was totally prevented by Trolox, a powerful antioxidant, DA uptake remained partially inhibited. Taken together, these data suggest that acidosis, in a degree encountered during ischemia, alters the high-affinity DA uptake in part by a mechanism that does not involve a Na+/K+ pump deficiency.