We have developed a high throughput screen using intact cells to identify muscarinic receptor agonists. Chinese hamster ovary cells stably transfected with the Ml muscarinic acetylcholine receptor (CHO-Ml) were pre-labeled with [3HJ-arachidonic acid (AA). Stimulation of muscarinic receptors with known muscarinic agonists resulted in release of AA from the cells into the culture medium. The released [3H]-AA in this assay was counted using both standard scintillation methods and Luma Plates. Because muscarinic antagonists do not cause release of AA, only agonists are identified. A follow-up screen using a competitive antagonist was used to confirm agonist properties of active compounds. This screen was relatively simple, reproducible, and compatible with many organic solvents and natural products growth media. Thus, it may be useful for the discovery of muscarinic agonists from natural product broths or synthetic compounds.
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