Dual, non-competitive interaction of lead with neuronal nicotinic acetylcholine receptors in N1E-115 neuroblastoma cells

Abstract

In cultured mouse neuroblastoma N1E-115 cells, inorganic lead (Pb 2+) affects inward currents induced by activation of neuronal type nicotinic acetylcholine receptors (nAChR) in a biphasic manner. At nanomolar concentrations a blocking action is observed, while at submillimolar concentrations this blocking effect is reversed, resulting in a U-shaped concentration–effect curve. Maximal block by 90% is observed at 1–3 μM Pb 2+. The interactions of Pb 2+ with nAChR were examined at the blocking concentration of 10 nM Pb 2+ and at 10 μM Pb 2+, presenting the reversal of block. The fitted E max for nAChR receptor activation by ACh was attenuated at both high and low Pb 2+ concentrations by 24% and 54%, respectively. The EC 50 values of the activation curves were not significantly altered; amounting to 53 μM, 64 μM and 86 μM ACh in the control situation and in the presence of 10 nM and 10 μM Pb 2+, respectively. Further, receptor desensitization and ion channel block by ACh were also not affected by Pb 2+. The results indicate that Pb 2+ affects nAChR in a dual manner that involves inhibition and potentiation, both by non-competitive interactions. Neuronal nAChR expressed in N1E-115 cells resemble a combination of α4 and β2 subunits, that constitute the predominant subunits in the central nervous system. The differential inhibition and potentiation of nAChR, together with the high sensitivity, are of interest with respect to Pb 2+ neurotoxicity.