Synaptoneurosomes, incubated with amphetamine, showed a biphasic dose-response change in activity of PKC and release of DA. Activity of particulate PKC activity and release of DA were decreased at 0.01-10.00 nM, while activity of both was increased at 1-10 microM. The effects of 0.1 nM amphetamine were attenuated by pretreatment with N-ethoxy-carbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), a peptide-coupling agent which inactivated DA receptors. They persisted if the autoreceptors were protected with sulpiride or apomorphine (0.05 mg/kg), prior to the treatment with EEDQ. In these protected rats, the amphetamine-induced change in activity of PKC was attenuated by sulpiride. In contrast, the effects of the larger doses of amphetamine on the activity of PKC were not affected by pretreatment with EEDQ. Subcellular fractionation of tissues, incubated with 1 microM amphetamine, showed an increase in activity of particulate PKC, only in the synaptic plasma membrane fraction, while tissues incubated with reserpine showed a decrease in activity of particulate PKC, only in the vesicular fraction. Similar results were seen when synaptic plasma membrane or synaptic vesicles were incubated directly with amphetamine or reserpine. These findings suggest the presence of multiple metabolic pools of PKC: a reserpine-sensitive pool, present in synaptic vesicles and an amphetamine-sensitive pool, present in the synaptic plasma membrane. That the latter pool of PKC may be involved in the transport of DA was indicated by the good correlation between the ability of drugs to inhibit the activity of PKC and their ability to inhibit the amphetamine-induced release of DA.