van den Beukel I, van Kleef R G, Oortgiesen M
Research Institute of Toxicology, Utrecht University, The Netherlands.
Neurotoxicology. 1998 Dec;19(6):777-87.
The effects of the carbamate physostigmine and of the organophosphates (OPs) parathion, paraoxon and phenyl saligenin cyclic phosphate (PSP) were examined on different subtypes of neuronal nicotinic acetylcholine receptors (nAChR). Stimulation with 1 mM ACh induced transient nicotinic inward currents in mouse N1E-115 and human SH-SY5Y neuroblastoma and in locust thoracic ganglion cells. All four acetylcholinesterase (AChE) inhibitors reduced the nicotinic currents in a concentration-dependent manner. Parathion is about 50 times more potent in blocking nAChR, compared to its active AChE inhibiting metabolite paraoxon. The relative blocking potency of the different AChE inhibitors was the same in all cell types, and followed the order parathion > physostigmine > PSP > paraoxon. In N1E-115 cells the IC50 values of block amounted to 2 microM, 30 microM, 39 microM and 96 microM for parathion, physostigmine, PSP and paraoxon, respectively. In all cell types, the nicotinic currents were equally blocked by parathion. Human nAChR in SH-SY5Y cells appeared more sensitive to block by physostigmine, PSP and paraoxon, while these AChE inhibitors similarly inhibited nicotinic currents in insect cells and in mouse neuroblastoma cells. The observation that the concentration-dependence of block is different from that of AChE inhibition, indicates a distinct interaction of AChE inhibitors with nAChR. Only in locust cells physostigmine induced a non-desensitizing inward current, that appeared to originate from nAChR activation. Occasionally, the OPs were able to activate slow ionic currents in mouse, but not in human and locust cells. As the OP-induced agonistic activity in mouse cells was not associated with the blocking action, the target site appeared to be distinct from nAChR. These results show that AChE inhibitors block nAChR with different potencies, dependent on the compound and the receptor subtype, and may activate distinct ion currents in neuronal cells of different species origin.
研究了氨基甲酸酯类毒扁豆碱以及有机磷酸酯类（OPs）对硫磷、对氧磷和苯基水杨苷环磷酸酯（PSP）对神经元烟碱型乙酰胆碱受体（nAChR）不同亚型的作用。用1 mM乙酰胆碱（ACh）刺激可在小鼠N1E-115和人SH-SY5Y神经母细胞瘤以及蝗虫胸神经节细胞中诱导瞬时烟碱型内向电流。所有四种乙酰胆碱酯酶（AChE）抑制剂均以浓度依赖性方式降低烟碱型电流。与具有活性的AChE抑制代谢产物对氧磷相比，对硫磷阻断nAChR的效力约高50倍。不同AChE抑制剂的相对阻断效力在所有细胞类型中均相同，顺序为对硫磷＞毒扁豆碱＞PSP＞对氧磷。在N1E-115细胞中，对硫磷、毒扁豆碱、PSP和对氧磷的阻断IC50值分别为2 microM、30 microM、39 microM和96 microM。在所有细胞类型中，对硫磷对烟碱型电流的阻断作用相同。SH-SY5Y细胞中的人nAChR对毒扁豆碱、PSP和对氧磷的阻断似乎更敏感，而这些AChE抑制剂对昆虫细胞和小鼠神经母细胞瘤细胞中的烟碱型电流的抑制作用相似。阻断的浓度依赖性与AChE抑制的浓度依赖性不同这一观察结果表明，AChE抑制剂与nAChR存在独特的相互作用。仅在蝗虫细胞中，毒扁豆碱诱导了一种非脱敏性内向电流，该电流似乎源于nAChR的激活。偶尔，OPs能够在小鼠细胞中激活缓慢的离子电流，但在人和蝗虫细胞中则不能。由于OPs在小鼠细胞中诱导的激动活性与阻断作用无关，因此靶点似乎与nAChR不同。这些结果表明，AChE抑制剂以不同的效力阻断nAChR，这取决于化合物和受体亚型，并且可能在不同物种来源的神经元细胞中激活不同的离子电流。
