Departamento de Investigacíon en Hiperreactividad Bronquial, Instituto Nacional de Enfermedades Respiratorias, México DF, Mexico.
Exp Physiol. 2011 Apr;96(4):460-7. doi: 10.1113/expphysiol.2010.056440. Epub 2011 Jan 28.
In the resting state, motor neurons continuously release ACh through quantal and non-quantal mechanisms, the latter through vesicular ACh transporter (VAChT) and choline transporter (ChT). Although in skeletal muscle these mechanisms have been extensively studied, the non-quantal release (NQR) from parasympathetic neurons of airway smooth muscle has not been described. Here we corroborated that the organophosphate paraoxon (acetylcholinesterase inhibitor) induced a contraction blocked by atropine (muscarinic antagonist) in guinea-pig tracheal rings. This contraction was not modified by two blockers of evoked quantal release, tetrodotoxin (voltage-dependent Na(+) channel blocker) and ω-conotoxin GVIA (N-type Ca(2+) channel blocker), nor by the nicotinic blocker hexamethonium, suggesting that acetylcholine NQR could be responsible of the paraoxon-induced contraction. We confirmed that tetrodotoxin, and to some extent -conotoxin, abolished the evoked quantal ACh release induced by electrical field stimulation. Hemicholinium-3 (ChT inhibitor), but not vesamicol (VAChT inhibitor), caused a concentration-dependent inhibition of the response to paraoxon. The highest concentration of hemicholinium-3 left ∼75% of the response to electrical field stimulation, implying that inhibition of paraoxon-induced contraction was not due to depletion of neuronal vesicles. Non-neuronal sources of ACh released through organic cation transporters were discarded because their inhibition by quinine or corticosterone did not modify the response to paraoxon. Calcium-free medium abolished the effect of paraoxon, and NiCl(2), 2-aminoethyl diphenyl-borate and SKF 96365 partly inhibited it, suggesting that non-specific cation channels were involved in the acetylcholine NQR. We concluded that a Ca(2+)-dependent NQR of ACh is present in cholinergic nerves from guinea-pig airways, and that ChT is involved in this phenomenon.
在静息状态下，运动神经元通过量子和非量子机制持续释放 ACh，后者通过囊泡 ACh 转运体 (VAChT) 和胆碱转运体 (ChT)。虽然在骨骼肌中已经对这些机制进行了广泛的研究，但气道平滑肌副交感神经元的非量子释放 (NQR) 尚未描述。在这里，我们证实有机磷杀虫剂对氧磷 (乙酰胆碱酯酶抑制剂) 诱导豚鼠气管环产生收缩反应，该反应被阿托品 (毒蕈碱拮抗剂) 阻断。这种收缩反应不受两种触发量子释放的阻断剂的影响，即河豚毒素 (电压依赖性 Na(+) 通道阻断剂) 和 ω-芋螺毒素 GVIA (N 型 Ca(2+) 通道阻断剂)，也不受烟碱受体阻断剂六烃季铵的影响，表明乙酰胆碱 NQR 可能是对氧磷诱导的收缩反应的原因。我们证实河豚毒素在一定程度上 - 芋螺毒素可消除电刺激引起的量子 ACh 释放。海巴氯铵-3（ChT 抑制剂），但不是维拉帕米（VAChT 抑制剂），可浓度依赖性抑制对氧磷的反应。海巴氯铵-3 的最高浓度使电刺激引起的反应保留了约 75%，这表明抑制对氧磷诱导的收缩反应不是由于神经元囊泡耗竭所致。由于奎宁或皮质酮抑制有机阳离子转运体释放的非神经元来源的 ACh 并没有改变对氧磷的反应，因此排除了这种可能性。无钙介质可消除对氧磷的作用，NiCl2、2-氨基乙基二苯硼酸和 SKF 96365 部分抑制了该作用，表明非特异性阳离子通道参与了乙酰胆碱的 NQR。我们的结论是，豚鼠气道胆碱能神经存在 Ca(2+) 依赖性 ACh 的 NQR，ChT 参与了这一现象。
