MRGPRX1 is an orphan receptor. MRGPRX1 is probably involved in the function of nociceptive neurons. It may regulate nociceptor function and/or development, including the sensation or modulation of pain. MRGPRX1 is potently activated by enkephalins including BAM22 (bovine adrenal medulla peptide 22) and BAM (8-22). BAM22 is the most potent compound and evoked a large and dose-dependent release of intracellular calcium in stably transfected cells. G(alpha)q proteins are involved in the calcium-signaling pathway. MRGPRX1 is activated by the antimalarial drug, chloroquine and may mediate chloroquine-induced itch, in an histamine-independent manner.