. This observation provided an opportunity to map the determinants of receptor affinity exhibited by BIBN4096BS and the truncated analogs, Compounds 1 and 2. All three compounds exhibited higher affinity for the human receptor, human CRLR/human RAMP1, than for the rat receptor, rat CRLR/rat RAMP1. We have now demonstrated that this species selectivity was directed exclusively by RAMP1. By generating recombinant human/rat CRLR/RAMP1 receptors, we demonstrated that co-expression of human CRLR with rat RAMP1 produced rat receptor pharmacology, and vice versa. Moreover, with rat/human RAMP1 chimeras and site-directed mutants, we have identified a single amino acid at position 74 of RAMP1 that modulates the affinity of small molecule antagonists for CRLR/RAMP1. Replacement of lysine 74 in rat RAMP1 with tryptophan (the homologous amino acid in the human receptor) resulted in a >100-fold increase in antagonist affinities, similar to the K i values for the human receptor. These observations suggest that important determinants of small molecule antagonist affinity for the CGRP receptor reside within the extracellular region of RAMP1 and provide evidence that this receptor accessory protein may participate in antagonist binding.CGRP is a 37-amino acid neuropeptide that is expressed in a variety of cell types in both the central and peripheral nervous systems (5). In many tissues, CGRP-containing fibers are closely associated with blood vessels (6). Among the various physiological functions reported for CGRP, the most pronounced is vasodilation. CGRP is the most powerful of the vasodilator transmitters (7), and its vasoactive effects have been demonstrated in a variety of blood vessels (8), including those in the cerebral, coronary, and mesenteric vasculature.Mounting evidence suggests that CGRP is involved in the pathophysiology of migraine headache (9). Migraine is thought to be associated with dilation of cerebral blood vessels and activation of the trigeminovascular system (10). During the headache phase of a migraine, CGRP levels are elevated in the cranial circulation (11, 12). Successful treatment of the headache with sumatriptan resulted in normalization of CGRP levels (12), thus implicating CGRP in the pathophysiology of this disorder. Moreover, intravenous administration of CGRP to migraineurs induced a delayed migrainous headache in some patients (13). These observations suggest that inhibition of CGRP-mediated vasodilation may have therapeutic utility in the treatment of migraine.Research in the area of CGRP has intensified in recent years due in large part to the identification of its receptor, CRLR 1 (14), and the cloning of the receptor activity-modifying proteins (RAMPs) (1) and receptor component protein (15). CGRP activity is mediated by the G s -coupled G-protein-coupled receptor (GPCR), CRLR, which shares 55% homology with the calcitonin receptor. In an elegant study, McLatchie et al. (1) demonstrated that functional CGRP and adrenomedullin receptors are both derived from CRLR and that the phenotype i...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.