Amyloid- (A) accumulation and aggregation are thought to contribute to the pathogenesis of Alzheimer's disease (AD). In AD, there is a selective decrease in the numbers of radioligand binding sites corresponding to the most abundant nicotinic acetylcholine receptor (nAChR) subtype, which contains human ␣4 and 2 subunits (h␣42-nAChR). However, the relationships between these phenomena are uncertain, and effects of A on h␣42-nAChR function have not been investigated in detail. We first confirmed expression of h␣4 and h2 subunits as messenger RNA in transfected, human SH-EP1 cells by reverse transcription-polymerase chain reaction and mRNA fluorescence in situ hybridization analyses. Immunoprecipitation Western analyses confirmed ␣4 and 2 subunit protein expression and coassembly. Whole cell current recording demonstrated heterologous expression in SH-EP1-h␣42 cells of functional h␣42-nAChRs with characteristic responses to nicotinic agonists or antagonists. Nicotine-induced whole cell currents were suppressed by A 1-42 in a dosedependent manner. Functional inhibition was selective for A 1-42 compared with the functionally inactive, control peptide A 40 -1 . A 1-42 -mediated inhibition of h␣42-nAChR function was non-competitive, voltage-independent, and use-independent. Pre-loading of cells with guanyl-5-yl thiophosphate failed to prevent A 1-42 -induced inhibition, suggesting that down-regulation of h␣42-nAChR function by A 1-42 is not mediated by nAChR internalization. Sensitivity to A 1-42 antagonism at 1 nM was evident for h␣42-nAChRs, but not for heterologously expressed human ␣7-nAChRs, although both nAChR subtypes were functionally inhibited by 100 nM A 1-42 , with the magnitude of functional block being higher for 100 nM A 1-42 acting on h␣7-nAChRs. These findings suggest that h␣42-nAChRs are sensitive and perhaps pathophysiologically relevant targets for A neurotoxicity in AD.Alzheimer's disease (AD) 1 is a progressive, neurodegenerative disorder manifest as a severe impairment of learning and memory. Pathophysiological hallmarks of AD include extracellular deposits of -amyloid peptide (A) in senile plaques, formation of intraneuronal neurofibrillary tangles, and cholinergic neuron death (1). Although the precise mechanisms of AD pathogenesis are only partially understood, it is now widely accepted that the accumulation and aggregation of A 1-42 plays a key role in the disease (2). Evidence has indicated an interaction between A and the cholinergic system (3). For example, very low concentrations (pico to nanomolar) of A can directly induce cholinergic hypofunction (4 -6). It has been reported that solubilized A inhibits several steps of acetylcholine synthesis and release (4, 7), inhibits cholinergic enzyme activity (6), impairs cholinergic metabolism and neurotransmission (8 -10), and depresses hippocampal synaptic function (11).Recent evidence suggests possible roles for nicotinic acetylcholine receptors (nAChRs) as central targets for A-induced neurotoxicity manifest as...