Shen M, Piser T M, Seybold V S, Thayer S A
Department of Pharmacology, University of Minnesota Medical School, Minneapolis 55455, USA.
J Neurosci. 1996 Jul 15;16(14):4322-34. doi: 10.1523/JNEUROSCI.16-14-04322.1996.
Activation of cannabinoid receptors inhibits voltage-gated Ca2+ channels and activates K+ channels, reminiscent of other G-protein-coupled signaling pathways that produce presynaptic inhibition. We tested cannabinoid receptor agonists for effects on excitatory neurotransmission between cultured rat hippocampal neurons. Reducing the extracellular Mg2+ concentration to 0.1 mM elicited repetitive, transient increases in intracellular Ca2+ concentration ([Ca2+]i spikes) that resulted from bursts of action potentials, as measured by combined whole-cell current clamp and indo-1-based microfluorimetry. Pharmacological characterization indicated that the [Ca2+]i spikes required glutamatergic synaptic transmission. Cannabinoid receptor ligands inhibited stereoselectively the frequency of [Ca2+]i spiking in the rank order of potency: CP 54,939 > CP 55,940 > Win 55,212-2 > anandamide, with EC50 values of 0.36, 1.2, 2.7, and 71 nM, respectively. CP 55,940 was potent, but not efficacious, and reversed the inhibition produced by Win 55,212-2, indicating that it is a partial agonist. Inhibition of [Ca2+]i spiking by Win 55,212-2 was prevented by treatment of cultures with active, but not heat-treated, pertussis toxin. Win 55,212-2 (100 nM) inhibited stereoselectively CNQX-sensitive excitatory postsynaptic currents (EPSCs) elicited by presynaptic stimulation with an extracellular electrode, but did not affect the presynaptic action potential or currents elicited by direct application of kainate. Consistent with a presynaptic site of action, Win 55,212-2 increased both the number of response failures and the coefficient of variation of the evoked EPSCs. In contrast, cannabimimetics did not affect bicuculline-sensitive inhibitory postsynaptic currents. Thus, activation of cannabinoid receptors inhibits the presynaptic release of glutamate via an inhibitory G-protein.
大麻素受体的激活会抑制电压门控性Ca2+通道并激活K+通道，这与其他产生突触前抑制的G蛋白偶联信号通路类似。我们测试了大麻素受体激动剂对培养的大鼠海马神经元之间兴奋性神经传递的影响。将细胞外Mg2+浓度降至0.1 mM会引发由动作电位爆发导致的细胞内Ca2+浓度（[Ca2+]i尖峰）的重复性、短暂性增加，这是通过全细胞电流钳和基于indo-1的显微荧光测定法测量的。药理学特性表明，[Ca2+]i尖峰需要谷氨酸能突触传递。大麻素受体配体以效力顺序立体选择性地抑制[Ca2+]i尖峰的频率：CP 54,939 > CP 55,940 > Win 55,212-2 > 花生四烯乙醇胺，EC50值分别为0.36、1.2、2.7和71 nM。CP 55,940具有强效，但效果不佳，并且能逆转Win 55,212-2产生的抑制作用，表明它是一种部分激动剂。用活性百日咳毒素而非热处理的百日咳毒素处理培养物可防止Win 55,212-2对[Ca2+]i尖峰的抑制。Win 55,212-2（100 nM）立体选择性地抑制了用细胞外电极进行突触前刺激所引发的对CNQX敏感的兴奋性突触后电流（EPSC），但不影响突触前动作电位或直接应用海人酸所引发的电流。与突触前作用位点一致，Win 55,212-2增加了反应失败的次数以及诱发的EPSC的变异系数。相比之下，大麻模拟物不影响对荷包牡丹碱敏感的抑制性突触后电流。因此，大麻素受体的激活通过抑制性G蛋白抑制谷氨酸的突触前释放。
