The invention provides an assay system for detecting a molecule that interacts with a membrane channel, the assay system including cell membranes including one or more membrane channels; support bodies including scintillant and a coupling agent that associates with the cell membrane; a ligand that is selected to bind the membrane channel, the ligand including a scintillant-activating label. According to the invention, association of the support bodies with the cell membrane and binding of the ligand to the membrane channel results in emission from the scintillant of the support bodies, and, in the presence of a test molecule that interacts with the membrane channel, the emission from the scintillant of the support bodies changes. Methods of identifying a molecule that interacts with a cell membrane channel are also described.