Price Theodore J, Patwardhan Amol, Akopian Armen N, Hargreaves Kenneth M, Flores Christopher M
Department of Pharmacology, The University of Texas Health Science Center at San Antonio, San Antonio, TX, U.S.A.
Br J Pharmacol. 2004 May;142(2):257-66. doi: 10.1038/sj.bjp.0705778.
The prototypical aminoalkylindole cannabinoid WIN 55,212-2 (WIN-2) has been shown to produce antihyperalgesia through a peripheral mechanism of action. However, it is not known whether WIN-2 exerts this action directly via cannabinoid receptors located on primary afferents or if other, perhaps indirect or noncannabinoid, mechanisms are involved. To address this question, we have examined the specific actions of WIN-2 on trigeminal ganglion (TG) neurons in vitro by quantifying its ability to modulate the evoked secretion of the proinflammatory neuropeptide CGRP as well as the inflammatory mediator-induced generation of cAMP. WIN-2 evoked CGRP release from TG neurons in vitro (EC(50)=26 microm) in a concentration- and calcium-dependent manner, which was mimicked by the cannabinoid receptor-inactive enantiomer WIN 55,212-3 (WIN-3). Moreover, WIN-2-evoked CGRP release was attenuated by the nonselective cation channel blocker ruthenium red but not by the vanilloid receptor type 1 (TRPV1) antagonist capsazepine, suggesting that, unlike certain endogenous and synthetic cannabinoids, WIN-2 is not a TRPV1 agonist but rather acts at an as yet unidentified cation channel. The inhibitory effects of WIN-2 on TG neurons were also examined. WIN-2 neither inhibited capsaicin-evoked CGRP release nor did it inhibit forskolin-, isoproteranol- or prostaglandin E(2)-stimulated cAMP accumulation. On the other hand, WIN-2 significantly inhibited (EC(50)=1.7 microm) 50 mm K(+)-evoked CGRP release by approximately 70%. WIN-2 inhibition of 50 mm K(+)-evoked CGRP release was not reversed by antagonists of cannabinoid type 1 (CB1) receptor, but was mimicked in magnitude and potency (EC(50)=2.7 microm) by its cannabinoid-inactive enantiomer WIN-3. These findings indicate that WIN-2 exerts both excitatory and inhibitory effects on TG neurons, neither of which appear to be mediated by CB1, CB2 or TRPV1 receptors, but by a novel calcium-dependent mechanism. The ramifications of these results are discussed in relation to our current understanding of cannabinoid/vanilloid interactions with primary sensory neurons.
典型的氨基烷基吲哚类大麻素WIN 55,212-2(WIN-2)已被证明通过外周作用机制产生抗痛觉过敏作用。然而,尚不清楚WIN-2是直接通过位于初级传入神经上的大麻素受体发挥这种作用,还是涉及其他机制,可能是间接的或非大麻素机制。为了解决这个问题,我们通过量化WIN-2调节促炎神经肽降钙素基因相关肽(CGRP)诱发分泌的能力以及炎症介质诱导的环磷酸腺苷(cAMP)生成,在体外研究了WIN-2对三叉神经节(TG)神经元的具体作用。WIN-2在体外以浓度和钙依赖性方式诱发TG神经元释放CGRP(半数有效浓度[EC50]=26微摩尔),大麻素受体无活性对映体WIN 55,212-3(WIN-3)也能模拟这种作用。此外,WIN-2诱发的CGRP释放被非选择性阳离子通道阻滞剂钌红减弱,但未被1型香草酸受体(TRPV1)拮抗剂辣椒素阻断,这表明与某些内源性和合成大麻素不同,WIN-2不是TRPV1激动剂,而是作用于一种尚未明确的阳离子通道。我们还研究了WIN-2对TG神经元的抑制作用。WIN-2既不抑制辣椒素诱发的CGRP释放,也不抑制福斯高林、异丙肾上腺素或前列腺素E2刺激的cAMP积累。另一方面,WIN-2显著抑制(EC50=1.7微摩尔)50毫摩尔钾离子诱发的CGRP释放约70%。WIN-2对50毫摩尔钾离子诱发的CGRP释放的抑制作用不能被1型大麻素(CB1)受体拮抗剂逆转,但其大麻素无活性对映体WIN-3在抑制程度和效力(EC50=2.7微摩尔)上能模拟这种作用。这些发现表明,WIN-2对TG神经元发挥兴奋和抑制作用,这两种作用似乎都不是由CB1、CB2或TRPV1受体介导的,而是通过一种新的钙依赖性机制。结合我们目前对大麻素/香草酸与初级感觉神经元相互作用的理解,讨论了这些结果的影响。