大麻素对大鼠三叉神经节神经元γ-氨基丁酸激活电流的抑制作用

Inhibition of GABA-activated Currents by Cannabinoids in Rat Trigeminal Neurons

目的探讨人工合成大麻素WIN55,212-2对大鼠三叉神经节神经元γ-氨基丁酸(GABA)激活电流(IGABA)的调制作用。方法采用全细胞膜片钳技术。结果①实验中大部分受检细胞(91.84%,99/108)对胞外给予GABA(10～1000μmol/L)敏感,可记录到具有浓度依赖性的内向电流,该电流可被GABAA受体特异性拮抗剂荷包牡丹碱(Bicuculline)阻断。②预加WIN55,212-2(0.03～10μmol/L)对IGABA产生抑制作用,该抑制作用呈可逆性、浓度依赖性和非电压依赖性。WIN55,212-2使IGABA的量效曲线明显下移,而两者的阈值基本不变;最大反应浓度时IGABA幅值减少了(48.83±4.78)%;两条曲线的半数有效浓度(EC50)值比较接近(36.85μmol/Lvs25.76μmol/L)。③WIN55,212-2对IGABA的抑制作用可被大麻素CB1受体选择性拮抗剂AM281阻断,不能被大麻素CB2受体选择性拮抗剂AM630阻断。细胞外灌流蛋白激酶C(PKC)的抑制剂BIM可部分逆转WIN55,212-2对IGABA的抑制作用。结论大麻素WIN55,212-2作用于CB1受体,部分通过激活PKC途径来减少GABAA受体介导的电流,加强突触前抑制作用,这可能是大麻素的外周镇痛机制之一。

Objective To investigate the effect of synthetic cannabinoids WIN55,212-2 on GABA-activated currents（IGABA） in rat trigeminal ganglion（TG） neurons.Methods Whole-cell patch clamp technique was used to record IGABA before and after perfusion of cannabinoids at different concentrations.Results The majority of examined neurons（91.84%,99/108） were sensitive to GABA（10-1 000 μmol/L）.The inward currents were activated by GABA in a concentration-dependent manner and blocked by bicuculline,a selective antagonist of the GABAA receptor.Pretreatment with WIN55,212-2（0.03-10 μmol/L） could significantly inhibit IGABA in reversible,concentration-dependent and voltage-independent manner.The concentration-response curve of GABA was shifted downward by WIN55,212-2 without any change of the threshold value.The EC50 values of two curves were very close（36.85 μmol/L vs 25.76 μmol/L） and WIN55,212-2 decreased the maximal amplitude of IGABA by（48.83±4.78）%.The inhibitory effect of WIN55,212-2 on IGABA could be reversed by AM281,a selective cannabinoid CB1 receptor antagonist,but not by AM630,a selective cannabinoid CB2 receptor antagonist.Pretreatment with BIM,a protein kinase C（PKC） inhibitor,could partially reverse the inhibitory effect of WIN55,212-2 on IGABA.Conclusion WIN55,212-2 inhibited IGABA by activating CB1 receptor and partially by activating PKC system.By inhibiting IGABA,CB1 suppressed the signal transmission at central end of primary sensory neuron by enhancing presynaptic inhibition,which may be one of the mechanisms by which cannabinoids participate in peripheral antinociception.