GBR-12909 effect on dopamine outflow depends on phosphorylation in the caudate nucleus of the rat

Modulation of the dopamine (DA) transporter inhibitor GBR-12909 effect on DA release by protein kinases and protein phosphatases was studied in slices of the rat caudate nucleus measuring DA outflow in the superfusate of static chambers. Activation of protein kinase A and C markedly enhanced the effect of GBR-12909, whereas protein kinase inhibition by H7 reduced the GBR-12909 effect. Inhibition of protein phosphatases (PPP) 1 and 2A by okadaic acid did not modify basal outflow of DA. However, after the addition of okadaic acid a dramatic and biphasic effect was found when DA outflow was enhanced by GBR-12909. Inhibition of PPP 2A enhanced extracellular DA levels, while inhibition of PPP 1 and 2A completely abolished the effect of GBR-12909. In contrast to tetrodotoxin, the voltage-activated calcium channel blocker omega-conotoxin MVIIC inhibited GBR-12909 effects on DA outflow. Additionally, in aCSF devoid of calcium GBR-12909 did not increase DA liberation. These results suggest a complex and strong influence of phosphorylation on GBR-12909 effects on calcium channel-dependent DA outflow at low-affinity piperazine binding sites in slices of the rat caudate nucleus in vitro.