Department of Pharmacology, CINVESTAV-IPN, Mexico.
Neuropharmacology. 2013 Aug;71:273-81. doi: 10.1016/j.neuropharm.2013.04.010. Epub 2013 Apr 16.
CaMKIIα is expressed at high density in the nucleus accumbens where it binds to postsynaptic D3 receptors inhibiting their effects. In striatonigral projections, activation of presynaptic D3 receptors potentiates D1 receptor-induced stimulation of cAMP production and GABA release. In this study we examined whether the presynaptic effects of D3 receptor stimulation in the substantia nigra reticulata (SNr) are modulated by Ca²⁺ activation of CaMKIIα. In SNr synaptosomes two procedures that increase cytoplasmic Ca²⁺, ionomycin and K⁺-depolarization, blocked the additional stimulation of cAMP accumulation produced by coactivating D3 and D1 dopamine receptors. The selective CaMKIIα inhibitor KN-62 reversed the blockade produced by ionomycin and K⁺-depolarization. Incubation in either Ca²-free solutions or with the selective Ca²⁺ blocker nifedipine, also reversed the blocking effects of K⁺-depolarization. Immunoblot studies showed that K⁺-depolarization increased CaMKIIα phosphorylation in a KN-62 sensitive manner and promoted CaMKIIα binding to D3 receptors. In K⁺-depolarized tissues, D3 receptors potentiated D1 receptor-induced stimulation of [³H]GABA release only when CaMKIIα was blocked with KN-62. In the presence of this inhibitor, the selective D3 agonist PD 128,907 reduced the ED₅₀ for the D1 agonist SKF 38393 from 56 to 4 nM. KN-62 also enhanced the effects of dopamine on depolarization induced [³H]GABA release. KN-62 changed ED₅₀ for dopamine from 584 to 56 nM. KN-62 did not affect D1 and D4 receptor responses. These experiments show that in striatonigral projections, CaMKIIα inhibits the action of D3 receptors in a Ca²⁺ dependent manner blocking their modulatory effects on GABA release. These findings suggest a mechanism through which the frequency of action potential discharge in presynaptic terminals regulates dopamine effects.
CaMKIIα 在伏隔核中高度表达，与突触后 D3 受体结合，抑制其作用。在纹状体苍白球投射中，激活突触前 D3 受体增强了 D1 受体诱导的 cAMP 产生和 GABA 释放。在这项研究中，我们研究了 D3 受体刺激在黑质网状部 (SNr) 的突触前效应是否受到 Ca²⁺ 激活的 CaMKIIα 的调节。在 SNr 突触小体中，两种增加细胞质 Ca²⁺ 的程序，离子霉素和 K⁺ 去极化，阻断了共激活 D3 和 D1 多巴胺受体产生的额外的 cAMP 积累刺激。选择性 CaMKIIα 抑制剂 KN-62 逆转了离子霉素和 K⁺ 去极化产生的阻断作用。在无 Ca²⁺ 溶液中孵育或用选择性 Ca²⁺ 阻断剂硝苯地平孵育，也逆转了 K⁺ 去极化的阻断作用。免疫印迹研究表明，K⁺ 去极化以 KN-62 敏感的方式增加 CaMKIIα 磷酸化，并促进 CaMKIIα 与 D3 受体结合。在 K⁺ 去极化的组织中，只有当 CaMKIIα 被 KN-62 阻断时，D3 受体才会增强 D1 受体诱导的 [³H]GABA 释放的刺激。在存在这种抑制剂的情况下，选择性 D3 激动剂 PD 128,907 将 D1 激动剂 SKF 38393 的 ED₅₀ 从 56 降低至 4 nM。KN-62 还增强了多巴胺对去极化诱导的 [³H]GABA 释放的作用。KN-62 将多巴胺的 ED₅₀ 从 584 降低至 56 nM。KN-62 不影响 D1 和 D4 受体反应。这些实验表明，在纹状体苍白球投射中，CaMKIIα 以 Ca²⁺ 依赖性方式抑制 D3 受体的作用，阻断其对 GABA 释放的调节作用。这些发现表明，动作电位发射在突触前末端的频率调节多巴胺作用的机制。
