The tachykinins belong to an evolutionary conserved family of peptide neurotransmitters that share the C-terminal sequence Phe-X-Gly-Leu-Met-NH2 and have an established role in neurotransmission. The mammalian tachykinins include substance P, neurokinin A (NKA) and neurokinin B (NKB) which exert their effects by binding to specific receptors. Tachykinin peptides are important in the mediation of many physiological and pathological processes including inflammation, pain, migraine headache and allergy induced asthma.
Three tachykinin receptor types have been characterized, NK-1, NK-2 and NK-3 which have preferential affinities for SP, NKA and NKB respectively. All three receptors share a high degree of sequence homology, have seven transmembrane spanning domains and similar signal transduction mechanisms (e.g. G-protein coupled activation of phospholipase C).