Development and optimization of a high-throughput electrophysiology assay for neuronal alpha4beta2 nicotinic...

Historically, the identification of alpha4beta2 nicotinic acetylcholine receptor ligands has been based on high-throughput radioligand binding, rubidium efflux assays and Ca++ flux assays using a fluorometric imaging plate reader (FLIPR). Among other approaches, low-throughput electrophysiological assays in Xenopus oocytes and two channel application "liquid filament" systems for mammalian cells have been commonly used. More recent technical innovations that have been introduced into the field of electrophysiology allow for automated simultaneous multi-channel operation. Here we report the development and optimization of a high-throughput electrophysiological assay for identifying functionally active alpha4beta2 nicotinic receptor ligands using such a system. Characterization of the test system yielded results comparable to those obtained by other investigators using conventional electrophysiological assays. For example, the concentration-response relationships obtained for alpha4beta2 receptor activation by acetylcholine and nicotine were best described by biphasic Hill equations, and the inhibition of alpha4beta2 receptor currents by the nicotinic antagonist dihydro-beta-erythroidine was consistent with previously published results. Functional up-regulation of alpha4beta2 receptors by prolonged exposure to nicotine or lower temperature was also confirmed. Using this methodology we were able to characterize the activation of alpha4beta2 receptors by multiple compounds in a mammalian cell expression system, exemplifying its utility for rapid identification of novel nicotinic ligands within a screening cascade. Our results demonstrate the utility of this electrophysiological tool for the discovery of alpha4beta2 nicotinic acetylcholine receptor ligands with potential applications in numerous clinical indications.