Repeated Amphetamine Couples Norepinephrine Transporter and Calcium Channel Activities in PC12 Cells

Abstract

Repeated intermittent amphetamine enhances efflux of dopamine through the dopamine transporter in rat basal ganglia and through the norepinephrine transporter in rat pheochromocytoma PC12 cells. Extracellular Ca 2ϩ is required for the detection of this enhancement in the rat. In this study, we examined the role of Ca 2ϩ and Ca 2ϩ channels in the enhanced amphetamine-induced dopamine efflux that develops in PC12 cells following repeated intermittent amphetamine. Repeated pretreatment of PC12 cells with 1 M amphetamine followed by a drug-free period increased amphetamine-induced efflux of dopamine compared with controls. The enhancement in amphetamine-induced dopamine efflux depended upon the presence of extracellular Ca 2ϩ and was inhibited by the blockade of N-type and L-type Ca 2ϩ channels. The enhanced dopamine efflux was not altered by tetanus toxin or reserpine, treatments that abrogate synaptic vesicle-mediated, exocytotic dopamine efflux. Measurement of intracellular Ca 2ϩ concentrations using fura-2/acetoxymethyl ester revealed that amphetamine increased intracellular Ca 2ϩ by a transporter-dependent mechanism. In amphetamine-pretreated cells, amphetamine elicited a greater increase in intracellular Ca 2ϩ ; this increase depended upon the presence of extracellular Ca 2ϩ and N-and L-type Ca 2ϩ channel activity. The enhanced amphetamine-induced dopamine efflux requires Ca 2ϩ /calmodulin kinase activity. In vehicle-treated cells, 1 M amphetamine inhibited the calmodulin kinase activity although it did not in amphetamine-pretreated cells. This study suggests that repeated intermittent amphetamine couples norepinephrine transporter activity and Ca 2ϩ signaling.

Dopamine Transporter Activity Mediates Amphetamine-Induced Inhibition of Akt through a Ca2+/Calmodulin-Dependent Kinase II-Dependent Mechanism

“…Repetitive administration of AMPH has been shown to activate kinases such as CaMKII in cell lines as well as in vivo (Iwata et al, 1997a;Kantor et al, 1999;Tan, 2002). Acute administration of AMPH has been shown to increase intracellular calcium (Gnegy, 2003;Kantor et al, 2004). Elevations in intracellular calcium could activate CaMKII activity (Hudmon and Schulman, 2002).…”

“…Because AMPH results in release of intracellular calcium Kantor et al, 2004), we asked whether CaMKII is involved in the AMPH-mediated Akt effect. We have shown that AMPH activates CaMKII in hDAT cells as well as in synaptosomes (Fig.…”

Kinase-dependent Regulation of Monoamine Neurotransmitter Transporters

“…Thus, Kantor et al (2004) described enhancement of DA efflux by PC-12 cells that was dependent on external Ca 2+ and is blocked by the voltage-gated Ca 2+ channel (VGCC) inhibitors v-conotoxin and nifedipine. The reader will recall that evidence suggests that DAT-mediated DA efflux after AMPH treatment relies more on intracellular Ca 2+ stores than extracellular Ca 2+ , suggesting differences in either NET versus DAT induction of efflux or the model systems used (e.g., presence of VGCCs).…”

Biogenic Amine Neurotransmitter Transporters: Just When You Thought You Knew Them

“…Similarly, Kantor and co-workers (28) found that chronic amphetamine elicits sensitized amphetamine-evoked DA release that can be blocked by CaMKII inhibitors. In PC-12 cells, amphetamineelicited Ca 2+ increases are mediated by L-and Ntype Ca 2+ channels (29), and thus it is possible that amphetamine activates CaMKII by changing levels of intracellular Ca 2+ .…”