Nicotinic acetylcholine receptors in cultured cells as targets of neurotoxic compounds

Abstract

Using electrophysiological techniques, effects of neurotoxicants were studied on mammalian neuronal and endplate type nicotinic acetylcholine receptors (nAChR) in N1E-115 cells and in BC3H 1 cells, respectively, and insect nAChR in locust neurons. Neuronal nAChR are highly sensitive to inorganic lead (Pb 2+). Between 1 n m and 3 μ m-Pb 2+ the ACh-induced inward current is blocked in a concentration-dependent manner (IC 50 = 19 n m; maximal effect (E max) = 90%). In contrast, the serotonin 5-HT 3 receptor is far less sensitive to Pb 2+ (IC 50 = 49 μ m). Surprisingly, between 10 μ m and 100 μ m Pb 2+ the blocking effect on the nAChR is reversed, and the kinetics of the ACh-induced inward current are delayed. Nitromethylene heterocyclic (NMH) compound constitute a new class of selective insecticides, that presumably affect insect nAChR. The effect of the NMH compound 1-(pyridin-3-yl-methyl)-2-nitromethylene-imidazolidine (PMNI) on the different subtypes of nAChR has been analysed. Distinct agonistic effects of PMNI on nAChR are observed on insect neurons only. Further, PMNI blocks nicotinic responses mediated by the different subtypes of nAChR in the following potency order: locust å neuronal type endplate type nAChR. These results demonstrate that the analysis of electrophysiological endpoints in cultured cells is a valuable approach to the investigation of target site selectivity and species specificity of neurotoxic compounds.