Department of Pharmacology, Faculty of Medicine and Odontology, University of the Basque Country, Barrio Sarriena s/n, Leioa E-48940, Bizkaia, Spain.
J Pharmacol Exp Ther. 2012 Aug;342(2):552-60. doi: 10.1124/jpet.112.194225. Epub 2012 May 16.
It has previously been shown that nitric oxide (NO) synthase is involved in the development of opioid tolerance. The aim of the present work was to study the effect of NO on μ-opioid receptor (MOR) desensitization. Furthermore, we explored the possible role of reactive oxygen species (ROS) in this effect. Single-unit extracellular and whole-cell patch-clamp recordings were performed on locus coeruleus (LC) neurons from rat brain slices. Perfusion with high concentrations of Met(5)-enkephalin (ME) caused a concentration-related reduction of opioid effect, reflecting the induction of homologous MOR desensitization. The NO donors sodium nitroprusside and diethylamine NONOate markedly enhanced the ME-induced MOR desensitization, although the acute effect of ME on K(+) conductance was not affected by sodium nitroprusside. Continuous perfusion with the antioxidants melatonin, trolox, 21-[4-(2,6-di-1-pyrrolidinyl-4-pyrrimidinyl)-1-piperazinyl]-pregna-1,4,9(11)-triene-3,20-dione(Z)-2-butenedioate (U74389G), and diethyldithiocarbamate prevented the effect of sodium nitroprusside on MOR desensitization, but they did not themselves alter the desensitization. Like sodium nitroprusside, the ROS-generating molecule H(2)O(2) enhanced MOR desensitization induced by ME. However, α(2)-adrenoceptor desensitization induced by noradrenaline was not modified by H(2)O(2), suggesting a selective action of ROS on MOR. Our results suggest that elevated levels of NO, which may be reached in pathological processes, enhance homologous desensitization of MOR in the LC, probably through a mechanism involving ROS generation.
先前的研究表明，一氧化氮合酶（NOS）参与了阿片类药物耐受的形成。本研究旨在探讨一氧化氮（NO）对μ-阿片受体（MOR）脱敏的影响，并进一步研究活性氧（ROS）在此过程中的可能作用。在大鼠脑片的蓝斑核（LC）神经元上进行了单细胞外记录和全细胞膜片钳记录。用高浓度的 Met(5)-脑啡肽（ME）灌流可引起阿片类药物作用的浓度依赖性降低，反映了同源 MOR 脱敏的诱导。NO 供体硝普钠和二乙基亚硝胺明显增强了 ME 诱导的 MOR 脱敏，尽管 ME 对 K+电导的急性作用不受硝普钠的影响。连续灌注抗氧化剂褪黑素、trolox、21-[4-(2,6-二-1-吡咯啉基-4-嘧啶基)-1-哌嗪基]-孕烷-1,4,9(11)-三烯-3,20-二酮（Z）-2-丁烯二酸盐（U74389G）和二乙基二硫代氨基甲酸盐可防止硝普钠对 MOR 脱敏的作用，但它们本身并不改变脱敏。与硝普钠一样，ROS 生成分子 H2O2 增强了由 ME 诱导的 MOR 脱敏。然而，去甲肾上腺素诱导的α2-肾上腺素受体脱敏不受 H2O2 影响，这表明 ROS 对 MOR 具有选择性作用。我们的结果表明，在病理过程中可能达到的高水平 NO 增强 LC 中 MOR 的同源脱敏，这可能是通过涉及 ROS 生成的机制。
