Köfalvi A, Pereira M F, Rebola N, Rodrigues R J, Oliveira C R, Cunha R A
Center for Neurosciences of Coimbra, University of Coimbra, Coimbra, Portugal.
Br J Pharmacol. 2007 Jun;151(4):551-63. doi: 10.1038/sj.bjp.0707252. Epub 2007 Apr 16.
Inhibitory CB(1) cannabinoid receptors and excitatory TRPV(1) vanilloid receptors are abundant in the hippocampus. We tested if two known hybrid endocannabinoid/endovanilloid substances, N-arachidonoyl-dopamine (NADA) and anandamide (AEA), presynapticaly increased or decreased intracellular calcium level (Ca(2+)) and GABA and glutamate release in the hippocampus.
Resting and K(+)-evoked levels of Ca(2+) and the release of [(3)H]GABA and [(3)H]glutamate were measured in rat hippocampal nerve terminals.
NADA and AEA per se triggered a rise of Ca(2+) and the release of both transmitters in a concentration- and external Ca(2+)-dependent fashion, but independently of TRPV(1), CB(1), CB(2), or dopamine receptors, arachidonate-regulated Ca(2+)-currents, intracellular Ca(2+) stores, and fatty acid metabolism. AEA was recently reported to block TASK-3 potassium channels thereby depolarizing membranes. Common inhibitors of TASK-3, Zn(2+), Ruthenium Red, and low pH mimicked the excitatory effects of AEA and NADA, suggesting that their effects on Ca(2+) and transmitter levels may be attributable to membrane depolarization upon TASK-3 blockade. The K(+)-evoked Ca(2+) entry and Ca(2+)-dependent transmitter release were inhibited by nanomolar concentrations of the CB(1) receptor agonist WIN55212-2; this action was sensitive to the selective CB(1) receptor antagonist AM251. However, in the low micromolar range, WIN55212-2, NADA and AEA inhibited the K(+)-evoked Ca(2+) entry and transmitter release independently of CB(1) receptors, possibly through direct Ca(2+) channel blockade.
We report here for hybrid endocannabinoid/endovanilloid ligands novel dual functions which were qualitatively similar to activation of CB(1) or TRPV(1) receptors, but were mediated through interactions with different targets.
抑制性大麻素CB(1)受体和兴奋性香草酸受体TRPV(1)在海马中大量存在。我们测试了两种已知的内源性大麻素/内源性香草酸混合物质，N-花生四烯酰多巴胺（NADA）和花生四烯乙醇胺（AEA），是否在突触前增加或降低细胞内钙水平（[Ca(2+)]i）以及海马中γ-氨基丁酸（GABA）和谷氨酸的释放。
在大鼠海马神经末梢测量静息和钾离子诱发的[Ca(2+)]i水平以及[3H]GABA和[3H]谷氨酸的释放。
NADA和AEA本身以浓度和细胞外钙依赖性方式引发[Ca(2+)]i升高以及两种递质的释放，但与TRPV(1)、CB(1)、CB(2)或多巴胺受体、花生四烯酸调节的钙电流、细胞内钙库和脂肪酸代谢无关。最近有报道称AEA可阻断TASK-3钾通道，从而使膜去极化。TASK-3的常见抑制剂锌离子（Zn(2+)）、钌红和低pH模拟了AEA和NADA的兴奋作用，表明它们对[Ca(2+)]i和递质水平的影响可能归因于TASK-3阻断后的膜去极化。纳摩尔浓度的CB(1)受体激动剂WIN55212-2可抑制钾离子诱发的钙内流和钙依赖性递质释放；此作用对选择性CB(1)受体拮抗剂AM251敏感。然而，在低微摩尔范围内，WIN55212-2、NADA和AEA独立于CB(1)受体抑制钾离子诱发的钙内流和递质释放，可能是通过直接阻断钙通道。
我们在此报告内源性大麻素/内源性香草酸混合配体具有新的双重功能，其性质与CB(1)或TRPV(1)受体激活相似，但通过与不同靶点的相互作用介导。
