σ2-receptor regulation of dopamine transporter via activation of protein kinase C

The elucidation of the mechanisms underlying sigma(2)-receptor activation and signal transduction is crucial to the understanding of sigma(2)-receptor function. Previous studies in our laboratory have demonstrated sigma(2)-receptor-mediated regulation of the dopamine transporter (DAT) as measured by amphetamine-stimulated release of [H-3] dopamine (DA) from both rat striatal slices and PC12 cells. The regulation of the DAT in the PC12 cell model was dependent upon activation of Ca2+/calmodulin-dependent kinase II. We have now studied the second messenger systems involved in sigma(2) receptor-mediated regulation of amphetamine-stimulated [H-3] DA release in rat striatal slices, including Ca2+/calmodulin-dependent kinase II, protein kinase C, and sources of calcium required for the enhancement of release produced by sigma(2)-receptor activation. The Ca2+/calmodulin-dependent kinase II inhibitors 1-[N,O-bis-(5-isoquionolinesulfonyl)]- N-methyl-L-tyrosyl-4-phenylpiperazine and N-[2-[[[3-(4'-chlorophenyl)-2-propenyl] methylamino] methyl] phenyl]- N-(2-hydroxyethyl)-4'- methoxy-benzenesulfonamide phosphate did not significantly affect the (+)-pentazocinemediated enhancement of amphetamine-stimulated [H-3] DA release. However, we found that an inhibitor of protein kinase C, 3-[1-[3-(dimethylamino) propyl]-1H-indol-3-yl)-1H-pyrrole- 2,5-dione, blocks the (+)-pentazocine-mediated enhancement in rat striatal slices. The protein kinase C activator phorbol 12-myristate 13-acetate, but not the inactive isophorbol 4alpha, 9alpha, 12alpha, 13alpha, 20-pentahydroxytiglia- 1,6-dien-3-one, enhanced the amphetamine-stimulated [H-3] DA release comparable to the enhancement seen by (+)- pentazocine alone. Additionally, the L-type voltage-dependent calcium channel inhibitor nitrendipine or prior treatment with thapsigargin, but not the N-type voltage-dependent calcium channel omega-conotoxin MVIIA, attenuated the (+) pentazocine- mediated enhancement. Together, these data suggest that activation of sigma(2)-receptors results in the regulation of DAT activity via a calcium- and protein kinase C-dependent signaling mechanism.