INHIBITORY EFFECTS OF NITRIC-OXIDE ON THE UPTAKE OF [H-3] DOPAMINE AND [H-3] GLUTAMATE BY STRIATAL SYNAPTOSOMES

Ten-minute incubation with 1 mM S-nitroso-L-cysteine (NO-CYS), a nitri c oxide (NO) generator, induced a 3.5-fold increase in the basal dopam ine (DA) efflux from rat striatal slices. Reduced hemoglobin (100 mu M ), a NO scavenger, blocked this response. Nomifensine (10 mu M), an in hibitor of high-affinity DA transport, reduced the NO-CYS effect by 39 %. In a synaptosomal preparation, NO-CYS induced a concentration-depen dent efflux of [H-3]DA that was also significantly inhibited by 10 mu M nomifensine. Because these findings indicated that NO could alter th e activity of the striatal DA transporter, we tested the effect of NO and NO-CYS on the uptake of [H-3]DA into crude striatal synaptosomes. Although both compounds inhibited [H-3]DA uptake with similar dose-res ponse characteristics (IC50 approximate to 300 mu M and approximate to 400 mu M, respectively),the effect of NO was quicker in onset. The pr esence of superoxide dismutase (30 U/ml) and catalase (50 U/ml) had a small impact on the NO-CYS inhibition of [H-3]DA uptake (1.8-fold incr ease in IC50). NO (1 mM) inhibited striatal [H-3]glutamate uptake by 2 3%, but lower concentrations had no significant effect. The duration o f the effect of NO gas on [H-3]DA uptake varied from <5 min to >10 min , depending on the concentration used. All concentrations of NO-CYS te sted produced an inhibition of [H-3]DA uptake that lasted at least 10 min. However, only concentrations less than or equal to 1 mM NO-CYS (o r NO) were washable. The effect of 3 mM NO-CYS lasted >20 min and coul d not be reversed by washing. Reduced hemoglobin (300 mu M) prevented the action of 3 mM NO-CYS, whereas methemoglobin had no effect. The ac tion of 3 mM NO-CYS was temperature dependent and took about 2 min to fully develop. Scatchard analysis revealed that NO-CYS diminished the capacity of the DA transporter without having a significant effect on the affinity. NO-CYS had no effect on striatal [H-3]- mazindol binding , suggesting that NO-CYS did not interact with the DA recognition site of the transporter. These data suggest that NO may play a role in the regulation of DA and, to a lesser extent, glutamate transport in the striatum.