There are four members (MRGX1-4) in the human MRGX familly. MRGX1 and MRGX2 receptors stimulate both G Alpha q- and G Alpha i -regulated pathways, while MRGX3 and MRGX4 receptors mainly activate G Alpha q-regulated pathways. G Alpha q proteins are involved in the calcium-signaling pathway downstream of the MRGX receptors. MRGX receptors are unique in that they are expressed in a subset of small dorsal root and trigeminal sensory neurons. Probably involved in the function of nociceptive neurons. May regulate nociceptor function and or development, including the sensation or modulation of pain. 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.