Undem Bradley J, Kollarik Marian
Johns Hopkins Asthma and Allergy Center, 5501 Hopkins Bayview Circle, Baltimore, MD 21224, USA.
J Pharmacol Exp Ther. 2002 Nov;303(2):716-22. doi: 10.1124/jpet.102.039727.
The effect of iodo-resiniferatoxin (I-RTX) on efferent function (tachykinergic contractions of airway smooth muscle) and afferent function (action potential discharge) of vagal C-fibers mediated by vanilloid receptor 1 (VR1) activation was studied in an isolated guinea pig airway preparation. I-RTX (1 microM) had no VR1 agonist activity in either the afferent or efferent assays. I-RTX (30 nM-1 microM) shifted the resiniferatoxin and capsaicin concentration-response curves for neurokinin-mediated contractions rightward but did not inhibit the maximum response. The pK(B) value calculated from 0.3 microM I-RTX against resiniferatoxin and capsaicin was 7.3 +/- 0.2 and 6.8 +/- 0.2, respectively, showing 10 to 30 times higher potency compared with capsazepine. The slope of Schild plot from the resiniferatoxin efferent studies deviated from unity (~0.6), suggesting complex interactions at VR1 binding site(s). This notion was further supported by lack of additional inhibitory effect of 1 microM I-RTX on capsaicin-evoked contractions compared with 0.3 microM I-RTX. Concentrations of I-RTX up to 1 microM had no effect on trypsin-induced neurokinin-mediated contractions, nor neurokinin A-induced contractions of guinea pig trachea. However, nonselective effects on airway smooth muscle contractions were noted with 10 microM I-RTX. In both afferent and efferent studies I-RTX (30 nM-1 microM) caused a substantial delay of the response to capsaicin. This led to an apparent increase in potency in experiments where the agonist was applied transiently, with insufficient time to reach equilibrium. I-RTX inhibited contractions induced by anandamide and action potential discharge induced by low pH, showing that the I-RTX-antagonism of VR1 does not strictly depend on the vanilloid nature of the agonist.
在离体豚鼠气道标本中，研究了碘代树脂毒素（I-RTX）对由香草酸受体1（VR1）激活介导的迷走神经C纤维传出功能（气道平滑肌速激肽能收缩）和传入功能（动作电位发放）的影响。I-RTX（1微摩尔）在传入或传出试验中均无VR1激动剂活性。I-RTX（30纳摩尔至1微摩尔）使树脂毒素和辣椒素介导的神经激肽收缩浓度-反应曲线右移，但不抑制最大反应。由0.3微摩尔I-RTX针对树脂毒素和辣椒素计算出的pK(B)值分别为7.3±0.2和6.8±0.2，表明其效力比辣椒素拮抗剂高10至30倍。树脂毒素传出研究的Schild图斜率偏离1（约为0.6），提示在VR1结合位点存在复杂相互作用。与0.3微摩尔I-RTX相比，1微摩尔I-RTX对辣椒素诱发的收缩缺乏额外抑制作用，进一步支持了这一观点。高达1微摩尔的I-RTX浓度对胰蛋白酶诱导的神经激肽介导的收缩以及豚鼠气管中神经激肽A诱导的收缩均无影响。然而，10微摩尔I-RTX对气道平滑肌收缩有非选择性作用。在传入和传出研究中，I-RTX（30纳摩尔至1微摩尔）均使对辣椒素的反应出现显著延迟。这导致在激动剂短暂应用且没有足够时间达到平衡的实验中，效力明显增加。I-RTX抑制了花生四烯乙醇胺诱导的收缩和低pH诱导的动作电位发放，表明I-RTX对VR1的拮抗作用并不严格依赖于激动剂的香草酸性质。
