Tang Q, Gandhoke R, Burritt A, Hruby V J, Porreca F, Lai J
Department of Pharmacology, The University of Arizona, Tucson, Arizona, USA.
J Pharmacol Exp Ther. 1999 Nov;291(2):760-5.
The opioid peptide dynorphin A elicits non-opioid receptor-mediated, neurotoxic response in vivo, which is blocked by pretreatment with MK-801, a noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonist. In the present study, we examined the possible direct interaction of dynorphin A on the NMDAR. A nonopioid dynorphin A analog, (125)I-(des-tyrosyl) dynorphin A(2-17), was used in radioligand binding analysis on rat cortical brain membranes. This radioligand exhibited a saturable, specific binding at high affinity with a K(d) value of 9.4+/-1.6 nM and maximal binding of 2.4+/-0.6 pmol/mg protein. This binding site was associated with the NMDAR complex because it was modulated by a number of NMDAR ligands. Transient expression of the rat NR1a/NR2A complex in human embryonic kidney 293 cells confirmed a coexpression of (125)I-(des-tyrosyl) dynorphin A(2-17), [(3)H]CGP39,653, and [(3)H]MK-801 binding. These data provide direct evidence of the presence of a high-affinity binding site for dynorphin A on the NMDAR. The modulatory effect of the various NMDAR-selective ligands on dynorphin A binding suggests that dynorphin A may bind preferentially to the closed/desensitized state of the NMDAR. The physiological role of dynorphin A binding to the NMDAR remains to be established.
阿片肽强啡肽A在体内引发非阿片受体介导的神经毒性反应，该反应可被非竞争性N-甲基-D-天冬氨酸受体（NMDAR）拮抗剂MK-801预处理所阻断。在本研究中，我们检测了强啡肽A与NMDAR之间可能存在的直接相互作用。一种非阿片类强啡肽A类似物，即(125)I-(去酪氨酸)强啡肽A(2 - 17)，被用于大鼠大脑皮层细胞膜的放射性配体结合分析。这种放射性配体在高亲和力下表现出可饱和的特异性结合，解离常数（K(d)）值为9.4±1.6 nM，最大结合量为2.4±0.6 pmol/mg蛋白。该结合位点与NMDAR复合物相关，因为它受到多种NMDAR配体的调节。大鼠NR1a/NR2A复合物在人胚肾293细胞中的瞬时表达证实了(125)I-(去酪氨酸)强啡肽A(2 - 17)、[(3)H]CGP39,653和[(3)H]MK-801结合的共表达。这些数据提供了强啡肽A在NMDAR上存在高亲和力结合位点的直接证据。各种NMDAR选择性配体对强啡肽A结合的调节作用表明，强啡肽A可能优先结合于NMDAR的关闭/失敏状态。强啡肽A与NMDAR结合的生理作用仍有待确定。
