Cells expressing significant current evoked by a brief agonist pulse (e.g. acetylcholine) are tested for their response to test compounds using a protocol of pre- and co-application of the compound.
We use a pre-application of 45 s and co-application of 10 s with the natural agonist. The advantage of this screening protocol is the possibility to reveal agonistic effects during the pre-application and modulatory or inhibitory effects of the compound during the co-application. The percentage of agonism, positive modulation (PAM), antagonism, desensitization or recovery is calculated compared to the reference natural agonist peak current.