Weatherspoon J K, Werling L L
Department of Pharmacology, The George Washington University Medical Center, Washington, DC, USA.
J Pharmacol Exp Ther. 1999 Apr;289(1):278-84.
An important regulatory mechanism of synaptic dopamine (DA) levels is activation of the dopamine transporter (DAT), which is a target for many drugs of abuse, including amphetamine (AMPH). sigma receptors are located in dopaminergic brain areas critical to reinforcement. We found previously that agonists at sigma2 receptors enhanced the AMPH-stimulated release of [3H]DA from slices of rat caudate-putamen. In the present study, we modeled this response in undifferentiated pheochromocytoma-12 (PC12) cells, which contain both the DAT and sigma2 receptors but not neural networks that can complicate investigation of individual neuronal mechanisms. We found that enhancement of AMPH-stimulated [3H]DA release by the sigma agonist (+)-pentazocine was blocked by sigma2 receptor antagonists. Additionally, the reduction in the effect of (+)-pentazocine by the inclusion of ethylene glycol bis(beta-aminoethyl ether)-N,N,N', N'-tetraacetic acid led us to hypothesize that sigma2 receptor activation initiated a Ca2+-dependent process that resulted in enhancing the outward flow of DA via the DAT. The source of Ca2+ required for the enhancement of reverse transport did not appear to be via N- or L-type voltage-dependent Ca2+ channels, because it was not affected by nitrendipine or omega-conotoxin. However, two inhibitors of Ca2+/calmodulin-dependent protein kinase II blocked enhancement in AMPH-stimulated release by (+)-pentazocine. Our findings suggest that sigma2 receptors are coupled to the DAT via a Ca2+/calmodulin-dependent protein kinase II transduction system in PC12 cells, and that sigma2 receptor antagonists might be useful in the treatment of drug abuse by blocking elevation of DA levels via reversal of the DAT.
突触多巴胺（DA）水平的一个重要调节机制是多巴胺转运体（DAT）的激活，DAT是包括苯丙胺（AMPH）在内的许多滥用药物的作用靶点。σ受体位于对强化作用至关重要的多巴胺能脑区。我们之前发现，σ2受体激动剂可增强AMPH刺激的大鼠尾状核-壳核切片中[3H]DA的释放。在本研究中，我们在未分化的嗜铬细胞瘤-12（PC12）细胞中模拟了这种反应，PC12细胞同时表达DAT和σ2受体，但不含有可能使单个神经元机制研究复杂化的神经网络。我们发现，σ激动剂（+）-喷他佐辛对AMPH刺激的[3H]DA释放的增强作用被σ2受体拮抗剂阻断。此外，加入乙二醇双（β-氨基乙基醚）-N，N，N'，N'-四乙酸后（+）-喷他佐辛作用的减弱使我们推测，σ2受体激活启动了一个Ca2+依赖的过程，该过程导致通过DAT增强DA的外流。反向转运增强所需的Ca2+来源似乎不是通过N型或L型电压依赖性Ca2+通道，因为它不受尼群地平和ω-芋螺毒素的影响。然而，两种Ca2+/钙调蛋白依赖性蛋白激酶II抑制剂阻断了（+）-喷他佐辛对AMPH刺激释放的增强作用。我们的研究结果表明，在PC12细胞中，σ2受体通过Ca2+/钙调蛋白依赖性蛋白激酶II转导系统与DAT偶联，并且σ2受体拮抗剂可能通过阻断DAT逆转导致的DA水平升高而有助于治疗药物滥用。
