Lee J-J, Hahm E-T, Min B-I, Han S-H, Cho J-J, Cho Y-W
Department of Physiology, College of Medicine, Kyung Hee University, Seoul 130-701, South Korea.
Neuropharmacology. 2003 Apr;44(5):573-83. doi: 10.1016/s0028-3908(03)00039-x.
The periaqueductal gray (PAG) is the main target site of the opioid-induced analgesia. The present study was designed to examine the roles of protein kinase A (PKA) and C (PKC) in the opioid-induced modulation of the currents activated by an inhibitory neurotransmitter, gamma-aminobutyric acid (GABA). The PAG neurons were acutely isolated and voltage-clamped under the nystatin-perforated patch-clamp mode. The GABA-activated current was sensitively blocked by a GABA(A) receptor antagonist, bicuculline, and selectively carried by chloride ions. The GABA(A) receptor-activated Cl(-) current was potentiated by a mu-opioid receptor agonist, [D-Ala(2),N-MePhe(4),Gly(5)-ol]-enkephalin acetate (DAMGO). The GABA response was also potentiated by phorbol-12-myristate-13-acetate (PMA). Pretreatment with PMA occluded the DAMGO potentiation. However, both chelerythrine and 2-[1-(3-dimethylaminopropyl)indol-3-yl]-3-(indol-3-yl) maleimide (GF109203X) also potentiated the GABA response. Pretreatment with chelerythrine or GF109203X also occluded the DAMGO potentiation. Meanwhile, the GABA response was potentiated by N-(2-[p-bromocinnamylamino]-ethyl)-5-isoquinolinesulfonamide (H-89), while not altered by forskolin. Pretreatment with H-89 occluded the potentiation effect of DAMGO on the GABA response. In addition, the DAMGO effect was completely blocked by pretreatment with forskolin. From the result, it can be suggested that activation of mu-opioid receptor potentiates the GABA(A) response through the mediation of PKA inhibition, and that PKC is not directly involved in the action mechanism of DAMGO.
导水管周围灰质（PAG）是阿片类药物诱导镇痛的主要靶点。本研究旨在探讨蛋白激酶A（PKA）和蛋白激酶C（PKC）在阿片类药物诱导的对抑制性神经递质γ-氨基丁酸（GABA）激活电流的调节中的作用。在制霉菌素穿孔膜片钳模式下对急性分离的PAG神经元进行电压钳制。GABA激活电流被GABA（A）受体拮抗剂荷包牡丹碱敏感阻断，并选择性地由氯离子携带。μ-阿片受体激动剂[D-丙氨酸（2），N-甲基苯丙氨酸（4），甘氨酸（5）-醇]-脑啡肽乙酸盐（DAMGO）增强了GABA（A）受体激活的Cl⁻电流。佛波醇-12-肉豆蔻酸酯-13-乙酸酯（PMA）也增强了GABA反应。用PMA预处理可消除DAMGO的增强作用。然而，白屈菜红碱和2-[1-（3-二甲基氨基丙基）吲哚-3-基]-3-（吲哚-3-基）马来酰亚胺（GF109203X）也增强了GABA反应。用白屈菜红碱或GF109203X预处理也消除了DAMGO的增强作用。同时，N-（2-[对溴肉桂酰胺基]乙基）-5-异喹啉磺酰胺（H-89）增强了GABA反应，而福司可林未改变其反应。用H-89预处理可消除DAMGO对GABA反应的增强作用。此外，用福司可林预处理可完全阻断DAMGO的作用。从结果可以推测，μ-阿片受体的激活通过PKA抑制的介导增强了GABA（A）反应，并且PKC不直接参与DAMGO的作用机制。
