Ulens C, Daenens P, Tytgat J
Laboratory of Toxicology, Faculty of Pharmaceutical Sciences, University of Leuven, Belgium.
Life Sci. 2000 Sep 29;67(19):2305-17. doi: 10.1016/s0024-3205(00)00820-1.
The effect of RGS4, a GTPase-activating protein, on the deactivation kinetics and basal activity of GIRK1/GIRK2 channels activated by the human kappa-opioid receptor (hKOR) was investigated. Co-expression in Xenopus oocytes of RGS4 reduces the basal GIRK1/GIRK2 current and strongly increases the percentage agonist-evoked K+ conductance. RGS4 reconstitutes the native gating kinetics by accelerating GIRK1/GIRK2 channel deactivation, a phenomenon also seen after activation with other 7 TM receptors (e.g. muscarine type). In the absence of RGS4, the GIRK1/GIRK2 conductance was increased by approx. 50% after hKOR stimulation with the kappa-selective opioid receptor ligand, U69593; however more importantly, at the end of the washout period it was dramatically reduced to about 60% of the basal conductance as measured before receptor stimulation. Furthermore, we found that repeated receptor stimulation causes an increase of the agonist-gated deactivation kinetics, without affecting the maximal and minimal conductance levels of GIRK1/GIRK2 channels during and after agonist application. Unlike in the absence of RGS4, coexpression with RGS4 completely abolished the reduction of basal conductance after agonist washout and the deactivation kinetics remained unaffected upon repeated agonist application. The results presented here clearly indicate that previous stimulation by agonists activating G protein-coupled receptors may have long-lasting, strong consequences on the following responses. Therefore, our study provides evidence for a novel modulation of deactivation kinetics of GIRK1/GIRK2 currents in the absence of RGS4.
研究了GTP酶激活蛋白RGS4对人κ-阿片受体（hKOR）激活的GIRK1/GIRK2通道失活动力学和基础活性的影响。在非洲爪蟾卵母细胞中共表达RGS4可降低GIRK1/GIRK2基础电流，并显著增加激动剂诱发的K⁺电导百分比。RGS4通过加速GIRK1/GIRK2通道失活来重构天然门控动力学，在用其他7次跨膜受体（如毒蕈碱型）激活后也观察到这种现象。在没有RGS4的情况下，用κ-选择性阿片受体配体U69593刺激hKOR后，GIRK1/GIRK2电导增加约50%；然而更重要的是，在洗脱期结束时，它急剧降至受体刺激前测量的基础电导的约60%。此外，我们发现重复的受体刺激会导致激动剂门控失活动力学增加，而不影响激动剂应用期间和之后GIRK1/GIRK2通道的最大和最小电导水平。与没有RGS4的情况不同，与RGS4共表达完全消除了激动剂洗脱后基础电导的降低，并且在重复应用激动剂时失活动力学保持不变。此处呈现的结果清楚地表明，激活G蛋白偶联受体的激动剂先前的刺激可能对后续反应产生持久、强烈的影响。因此，我们的研究为在没有RGS4的情况下GIRK1/GIRK2电流失活动力学的新型调节提供了证据。
