Discipline of Pharmacology and Brain and Mind Research Institute, University of Sydney, New South Wales, Australia.
Mol Pharmacol. 2012 Sep;82(3):473-80. doi: 10.1124/mol.112.079350. Epub 2012 Jun 11.
Prolonged agonist stimulation of the μ-opioid receptor (MOR) initiates receptor regulatory events that rapidly attenuate receptor-mediated signaling (homologous desensitization). Emerging evidence suggests that persistent MOR stimulation can also reduce responsiveness of effectors to other G-protein-coupled receptors, termed heterologous desensitization. However, the mechanisms by which heterologous desensitization is triggered by MOR stimulation are unclear. This study used whole-cell patch-clamp recordings of ligand activated G-protein-activated inwardly rectifying potassium channel currents in mouse brain slices containing locus ceruleus (LC) neurons to determine the effects of prolonged stimulation of MOR on α(2)-adrenoceptor (α(2)-AR) function. The results show distinct and sequential development of homologous and heterologous desensitization during persistent stimulation of MOR in LC neurons with Met(5)-enkephalin (ME). ME stimulation of MOR promoted rapid homologous desensitization that reached a steady state after 5 min and partially recovered over 30 min. Longer stimulation of MOR (10 min) induced heterologous desensitization of α(2)-AR function that exhibited slower recovery than homologous desensitization. Heterologous (but not homologous) desensitization required β-arrestin-2 (βarr-2) because it was nearly abolished in βarr-2-knockout (ko) mice. Heterologous (but not homologous) desensitization was also prevented by inhibition of ERK1/2 and c-Src signaling in wild-type (wt) mouse LC neurons. Heterologous desensitization may be physiologically relevant during exposure to high doses of opioids because α(2)-AR-mediated slow inhibitory postsynaptic currents were depressed in wt but not βarr-2 ko LC neurons after prolonged exposure to opioids. Together, these findings demonstrate a novel mechanism by which βarr-2 can regulate postsynaptic responsiveness to neurotransmitter release.
μ 阿片受体（MOR）的激动剂持续刺激会引发受体调节事件，从而迅速减弱受体介导的信号转导（同源脱敏）。新出现的证据表明，持续的 MOR 刺激也可以降低效应器对其他 G 蛋白偶联受体的反应性，称为异源脱敏。然而，MOR 刺激引发异源脱敏的机制尚不清楚。本研究使用包含蓝斑核（LC）神经元的小鼠脑片进行的配体激活 G 蛋白激活内向整流钾通道电流的全细胞膜片钳记录，以确定 MOR 持续刺激对 α(2)-肾上腺素能受体（α(2)-AR）功能的影响。结果表明，在 LC 神经元中，用 Met(5)-脑啡肽（ME）持续刺激 MOR 时，同源和异源脱敏会表现出不同的顺序发展。MOR 刺激 ME 促进了快速的同源脱敏，在 5 分钟后达到稳定状态，并在 30 分钟内部分恢复。更长时间的 MOR 刺激（10 分钟）诱导了 α(2)-AR 功能的异源脱敏，其恢复速度比同源脱敏慢。异源（但不是同源）脱敏需要β-arrestin-2（βarr-2），因为它在βarr-2 敲除（ko）小鼠中几乎被消除。在野生型（wt）小鼠 LC 神经元中，抑制 ERK1/2 和 c-Src 信号也可以防止异源（但不是同源）脱敏。在暴露于高剂量阿片类药物时，异源脱敏可能具有生理相关性，因为在长期暴露于阿片类药物后，wt 但不是 βarr-2 ko LC 神经元中的 α(2)-AR 介导的慢抑制性突触后电流被抑制。总之，这些发现表明了一种新的机制，通过该机制，βarr-2 可以调节突触后对神经递质释放的反应性。
