Patel Jyoti C, Witkovsky Paul, Avshalumov Marat V, Rice Margaret E
Department of Neurosurgery, New York University School of Medicine, New York, New York 10016, USA.
J Neurosci. 2009 May 20;29(20):6568-79. doi: 10.1523/JNEUROSCI.0181-09.2009.
Somatodendritic dopamine (DA) release in the substantia nigra pars compacta (SNc) shows a limited dependence on extracellular calcium concentration (Ca(2+)), suggesting the involvement of intracellular Ca(2+) stores. Here, using immunocytochemistry we demonstrate the presence of the sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase 2 (SERCA2) that sequesters cytosolic Ca(2+) into the endoplasmic reticulum (ER), as well as inositol 1,4,5-triphosphate receptors (IP(3)Rs) and ryanodine receptors (RyRs) in DAergic neurons. Notably, RyRs were clustered at the plasma membrane, poised for activation by Ca(2+) entry. Using fast-scan cyclic voltammetry to monitor evoked extracellular DA concentration (DA) in midbrain slices, we found that SERCA inhibition by cyclopiazonic acid (CPA) decreased evoked DA in the SNc, indicating a functional role for ER Ca(2+) stores in somatodendritic DA release. Implicating IP(3)R-dependent stores, an IP(3)R antagonist, 2-APB, also decreased evoked DA. Moreover, DHPG, an agonist of group I metabotropic glutamate receptors (mGluR1s, which couple to IP(3) production), increased somatodendritic DA release, whereas CPCCOEt, an mGluR1 antagonist, suppressed it. Release suppression by mGluR1 blockade was prevented by 2-APB or CPA, indicating facilitation of DA release by endogenous glutamate acting via mGluR1s and IP(3)R-gated Ca(2+) stores. Similarly, activation of RyRs by caffeine increased Ca(2+) and elevated evoked DA. The increase in DA release was prevented by a RyR blocker, dantrolene, and by CPA. Importantly, the efficacy of dantrolene was enhanced in low Ca(2+), suggesting a mechanism for maintenance of somatodendritic DA release with limited Ca(2+) entry. Thus, both mGluR1-linked IP(3)R- and RyR-dependent ER Ca(2+) stores facilitate somatodendritic DA release in the SNc.
黑质致密部（SNc）中树突体多巴胺（DA）释放对细胞外钙浓度（Ca(2+)）的依赖性有限，提示细胞内钙库参与其中。在此，我们运用免疫细胞化学方法证实了肌浆网/内质网钙ATP酶2（SERCA2）的存在，其可将胞质钙隔离到内质网（ER）中，同时在多巴胺能神经元中也证实了1,4,5-三磷酸肌醇受体（IP(3)Rs）和兰尼碱受体（RyRs）的存在。值得注意的是，RyRs聚集在质膜上，准备好通过钙内流被激活。利用快速扫描循环伏安法监测中脑切片中诱发的细胞外多巴胺浓度（DA），我们发现环匹阿尼酸（CPA）抑制SERCA会降低SNc中诱发的DA，表明内质网钙库在树突体多巴胺释放中具有功能作用。涉及IP(3)R依赖的钙库，IP(3)R拮抗剂2-APB也会降低诱发的DA。此外，I组代谢型谷氨酸受体（mGluR1s，其与IP(3)生成偶联）的激动剂DHPG会增加树突体多巴胺释放，而mGluR1拮抗剂CPCCOEt则会抑制它。mGluR1阻断导致的释放抑制可被2-APB或CPA阻止，表明内源性谷氨酸通过mGluR1s和IP(3)R门控钙库促进多巴胺释放。同样，咖啡因激活RyRs会增加Ca(2+)并提高诱发的DA。多巴胺释放的增加可被RyR阻滞剂丹曲林和CPA阻止。重要的是，在低Ca(2+)条件下丹曲林的功效增强，提示一种在钙内流有限时维持树突体多巴胺释放的机制。因此，mGluR1连接的IP(3)R和RyR依赖的内质网钙库均促进SNc中树突体多巴胺释放。
