Mechanisms underlying the effects of amphetamine on particulate PKC activity

Abstract

Amphetamine stimulates particulate protein kinase C (PKC) activity that is associated with the outward‐transport of dopamine (DA) (Giambalvo [2003] Synapse 49:125–133). This stimulatory effect requires intracellular calcium ([Ca]_i) and endogenous DA and when DA release is diminished, the inward‐transport of amphetamine inhibits PKC activity. This study examines the mechanisms involved. It was found that synaptoneurosomes incubated with amphetamine showed a dose‐dependent increase in phospholipase C and A₂ activities. Furthermore, pretreatments with the phospholipase C inhibitor D609 or the phospholipase A₂ inhibitors quinacrine or p‐bromophenacylbromide attenuated the amphetamine‐induced increase in PKC activity. This suggests that both phospholipases were essential for the amphetamine‐induced increase in PKC activity. The Na/Ca antiporter was also involved, since pretreatment with amiloride or benzamil attenuated the amphetamine‐induced increase in PKC activity. Since these drugs by themselves increased PKC activity, the return to basal activity after addition of amphetamine suggests that, in the absence of Na/Ca exchange, amphetamine had an inhibitory effect on PKC activity. This inhibitory effect might be due to the activation of phospholipase A₂ through an increase in intracellular pH induced by amphetamine. This was supported by the finding that pretreatment with dimethylamiloride, an inhibitor of the Na/H antiporter that increases intracellular [H⁺], attenuated the effects of amphetamine on PKC activity. Other drugs that decrease intracellular [H⁺] (ammonia, monensin) also inhibited PKC activity without Ca. In contrast to amphetamine, monensin had no effect on PKC activity with Ca. This could be related to its large differential effects on phospholipase A₂ vs. phospholipase C activity. Thus, the monensin‐mediated decrease in PKC activity seen without Ca was partially attenuated by pretreatment with quinacrine. Furthermore, when Na/Ca antiporter was inhibited with benzamil, monensin inhibited PKC activity. These results suggest that amphetamine, as well as monensin, may have dual effects on PKC activity, a Ca‐dependent stimulatory effect via phospholipase C, and an inhibitory effect via phospholipase A₂. Synapse 51:128–139, 2004.