Liu Man, Dilger James P
Department of Anesthesiology, Stony Brook University, Stony Brook, NY 11790, USA.
Anesth Analg. 2008 Aug;107(2):525-33. doi: 10.1213/ane.0b013e31817b4469.
Synergistic neuromuscular blocking effects have been observed clinically with certain pairs of nicotinic acetylcholine receptor (nAChR) competitive antagonists. The mechanism for synergy has not been elucidated. We tested the hypothesis that synergy arises from a differential selectivity of antagonists for the two ligand binding sites on adult human nAChR.
We expressed nAChR in BOSC23 cells. We applied ACh with or without antagonists to outside-out patches and measured macroscopic currents at room temperature. We determined the IC(90) for (+)-tubocurarine, metocurine, pancuronium, vecuronium, cisatracurium, rocuronium, and atracurium. For 15 combinations of two antagonists, we determined the IC(90) for one antagonist in the presence of the IC(70) of a second antagonist. We constructed isobolograms for 90% inhibition. For single antagonists, we measured inhibition of receptors containing mutations in the epsilon- and delta-subunits to determine site selectivity.
Two pairs of antagonists, metocurine+cisatracurium and cisatracurium+ atracurium exhibited additive inhibition. Ten combinations, including (+)-tubocurarine+ pancuronium and pancuronium+vecuronium, were highly synergistic such that the combination was two to three times more effective than expected for additivity. Three combinations were 1.5-1.6 times more effective than expected for additivity. Inhibition by (+)-tubocurarine and metocurine was sensitive to mutations in the epsilon-subunit only. Vecuronium was affected by the delta-subunit mutation only. Inhibition by other antagonists was decreased by mutations in either subunit.
Many combinations of antagonists exhibited synergistic effects on adult human nAChR. Synergy was observed with structurally similar and dissimilar antagonists. The degree of synergy did not always correlate well with site specificity assayed with mutants. In some, but not all cases, the synergy at the receptor level correlated with clinical determinations of synergy. We conclude that the synergistic actions of muscle relaxants can be partially explained by direct interactions with adult human nAChR.
临床上已观察到某些对烟碱型乙酰胆碱受体（nAChR）竞争性拮抗剂具有协同神经肌肉阻滞作用。协同作用的机制尚未阐明。我们检验了这样一种假设，即协同作用源于拮抗剂对成人nAChR上两个配体结合位点的选择性差异。
我们在BOSC23细胞中表达nAChR。我们在室温下，将有或无拮抗剂的乙酰胆碱应用于外翻膜片，并测量宏观电流。我们确定了（+）-筒箭毒碱、美库氯铵、泮库溴铵、维库溴铵、顺阿曲库铵、罗库溴铵和阿曲库铵的IC90。对于两种拮抗剂的15种组合，我们在第二种拮抗剂的IC70存在的情况下确定了一种拮抗剂的IC90。我们构建了90%抑制率的等效线图。对于单一拮抗剂，我们测量了含有ε和δ亚基突变的受体的抑制情况，以确定位点选择性。
两对拮抗剂，美库氯铵+顺阿曲库铵和顺阿曲库铵+阿曲库铵表现出相加抑制作用。十种组合，包括（+）-筒箭毒碱+泮库溴铵和泮库溴铵+维库溴铵，具有高度协同作用，使得该组合的效果比相加预期高两到三倍。三种组合的效果比相加预期高1.5 - 1.6倍。（+）-筒箭毒碱和美库氯铵的抑制作用仅对ε亚基的突变敏感。维库溴铵仅受δ亚基突变的影响。其他拮抗剂的抑制作用因任一亚基的突变而降低。
许多拮抗剂组合对成人nAChR表现出协同作用。在结构相似和不同的拮抗剂中均观察到协同作用。协同程度并不总是与用突变体测定的位点特异性密切相关。在一些但并非所有情况下，受体水平的协同作用与协同作用的临床判定相关。我们得出结论，肌肉松弛剂的协同作用可部分通过与成人nAChR的直接相互作用来解释。
