Ton Hoai T, Smart Amanda E, Aguilar Brittany L, Olson Thao T, Kellar Kenneth J, Ahern Gerard P
Department of Pharmacology and Physiology, Georgetown University, Washington, District of Columbia.
Department of Pharmacology and Physiology, Georgetown University, Washington, District of Columbia
Mol Pharmacol. 2015 Aug;88(2):256-64. doi: 10.1124/mol.115.098285. Epub 2015 May 11.
The α3β4 nicotinic acetylcholine receptor (nAChR) subtype is widely expressed in the peripheral and central nervous systems, including in airway sensory nerves. The nAChR subtype transduces the irritant effects of nicotine in tobacco smoke and, in certain brain areas, may be involved in nicotine addiction and/or withdrawal. Menthol, a widely used additive in cigarettes, is a potential analgesic and/or counterirritant at sensory nerves and may also influence nicotine's actions in the brain. We examined menthol's effects on recombinant human α3β4 nAChRs and native nAChRs in mouse sensory neurons. Menthol markedly decreased nAChR activity as assessed by Ca(2+) imaging, (86)Rb(+) efflux, and voltage-clamp measurements. Coapplication of menthol with acetylcholine or nicotine increased desensitization, demonstrated by an increase in the rate and magnitude of the current decay and a reduction of the current integral. These effects increased with agonist concentration. Pretreatment with menthol followed by its washout did not affect agonist-induced desensitization, suggesting that menthol must be present during the application of agonist to augment desensitization. Notably, menthol acted in a voltage-independent manner and reduced the mean open time of single channels without affecting their conductance, arguing against a simple channel-blocking effect. Further, menthol slowed or prevented the recovery of nAChRs from desensitization, indicating that it probably stabilizes a desensitized state. Moreover, menthol at concentrations up to 1 mM did not compete for the orthosteric nAChR binding site labeled by [(3)H]epibatidine. Taken together, these data indicate that menthol promotes desensitization of α3β4 nAChRs by an allosteric action.
α3β4烟碱型乙酰胆碱受体（nAChR）亚型在周围和中枢神经系统中广泛表达，包括气道感觉神经。该nAChR亚型可传导烟草烟雾中尼古丁的刺激作用，并且在某些脑区可能与尼古丁成瘾和/或戒断有关。薄荷醇是香烟中广泛使用的添加剂，在感觉神经处是一种潜在的镇痛药和/或抗刺激剂，也可能影响尼古丁在大脑中的作用。我们研究了薄荷醇对重组人α3β4 nAChRs和小鼠感觉神经元中天然nAChRs的影响。通过Ca(2+)成像、(86)Rb(+)外流和电压钳测量评估，薄荷醇显著降低了nAChR活性。薄荷醇与乙酰胆碱或尼古丁共同应用增加了脱敏作用，表现为电流衰减速率和幅度增加以及电流积分减少。这些作用随激动剂浓度增加而增强。用薄荷醇预处理后冲洗，并不影响激动剂诱导的脱敏作用，这表明在应用激动剂期间必须存在薄荷醇才能增强脱敏作用。值得注意的是，薄荷醇以电压非依赖性方式起作用，降低了单通道的平均开放时间而不影响其电导，这与简单的通道阻断作用不符。此外，薄荷醇减缓或阻止了nAChRs从脱敏状态的恢复，表明它可能稳定了脱敏状态。而且，浓度高达1 mM的薄荷醇不与[(3)H]依博加因标记的正构nAChR结合位点竞争。综上所述，这些数据表明薄荷醇通过变构作用促进α3β4 nAChRs的脱敏。
