Jaén Cristina, Doupnik Craig A
Department of Physiology & Biophysics, University of South Florida College of Medicine, 12901 Bruce B. Downs Blvd. MDC8, Tampa, FL 33612, USA.
Neuropharmacology. 2005 Sep;49(4):465-76. doi: 10.1016/j.neuropharm.2005.04.010.
"Regulators of G protein signaling" (RGS proteins) have profound effects on ion channels regulated by G protein-coupled receptor (GPCR) signaling, including the G protein-gated inwardly rectifying K+ (GIRK) channels that inhibit excitability of neuronal, endocrine, and cardiac cells. Here we describe the effects of an alternatively spliced "short" RGS3 isoform (RGS3s) in comparison to RGS4, on the temporal and steady-state gating properties of neuronal GIRK channels (Kir3.1/Kir3.2a) activated by either serotonin 1A (5-HT(1A)) receptors or muscarinic m2 receptors expressed in Chinese hamster ovary (CHO-K1) cells. RGS3s is abundantly expressed in brain and contains a unique short N-terminus via alternative splicing that distinguishes it from other RGS3 isoforms as well as other members of the B/R4 RGS gene subfamily. Our results indicate that RGS3s and RGS4 similarly affect the temporal and steady-state gating properties of 5-HT(1A) receptor-coupled Kir3.1/Kir3.2a channels, but differentially modulate muscarinic m2 receptor-coupled channels. RGS3s caused a significant approximately 45% reduction in the maximal acetylcholine (ACh)-evoked GIRK current amplitude and a marked shift in the steady-state ACh dose-response relation indicative of a reduction in functionally coupled m2 receptor-GIRK channel complexes. Yet RGS3s still accelerated the m2 receptor-dependent GIRK activation, deactivation, and acute desensitization time course consistent with the RGS-enhanced GAP activity that was also observed with RGS4. Several mechanisms that may contribute to the receptor-dependent effects of RGS3s are discussed with particular attention to the role of the distinct N-terminal domain. Our findings highlight the potential impact of selective RGS-GPCR interactions on neuronal GIRK channel function that may affect the properties of inhibitory postsynaptic potentials activated by different GPCR-GIRK channel complexes.
G蛋白信号调节因子（RGS蛋白）对受G蛋白偶联受体（GPCR）信号调控的离子通道有深远影响，包括抑制神经元、内分泌和心脏细胞兴奋性的G蛋白门控内向整流钾离子（GIRK）通道。在此，我们描述了一种选择性剪接的“短”RGS3亚型（RGS3s）与RGS4相比，对中国仓鼠卵巢（CHO-K1）细胞中表达的5-羟色胺1A（5-HT(1A)）受体或毒蕈碱型m2受体激活的神经元GIRK通道（Kir3.1/Kir3.2a）的时间和稳态门控特性的影响。RGS3s在大脑中大量表达，通过选择性剪接含有独特的短N端，这使其与其他RGS3亚型以及B/R4 RGS基因亚家族的其他成员区分开来。我们的结果表明，RGS3s和RGS4同样影响5-HT(1A)受体偶联的Kir3.1/Kir3.2a通道的时间和稳态门控特性，但对毒蕈碱型m2受体偶联通道的调节有所不同。RGS3s使最大乙酰胆碱（ACh）诱发的GIRK电流幅度显著降低约45%，并使稳态ACh剂量反应关系发生明显偏移，表明功能偶联的m2受体-GIRK通道复合物减少。然而，RGS3s仍加速了m2受体依赖性GIRK的激活、失活和急性脱敏时间进程，这与RGS4观察到的RGS增强的GAP活性一致。讨论了可能导致RGS3s受体依赖性效应的几种机制，特别关注了独特N端结构域的作用。我们的发现突出了选择性RGS-GPCR相互作用对神经元GIRK通道功能的潜在影响，这可能会影响由不同GPCR-GIRK通道复合物激活的抑制性突触后电位的特性。
