Impromidine (IMP) and arpromidine (ARP)-derived guanidines are more potent and efficacious guinea pig (gp) histamine H2-receptor (gpH 2R) than human (h) H2R agonists and histamine H 1-receptor (H1R) antagonists with preference for hH 1R relative to gpH1R. We examined NG-acylated imidazolylpropylguanidines (AIPGs), which are less basic than guanidines, at hH2R, gpH2R, rat H2R (rH2R), hH 1R, and gpH1R expressed in Sf9 cells as probes for ligand-specific receptor conformations. AIPGs were similarly potent H 2R agonists as the corresponding guanidines IMP and ARP, respectively. Exchange of pyridyl in ARP against phenyl increased AIPG potency 10-fold, yielding the most potent agonists at the hH 2R-G sα fusion protein and gpH2R-Gsα identified so far. Some AIPGs were similarly potent and efficacious at hH 2R-Gsα and gpH2R-Gsα. AIPGs stabilized the ternary complex in hH2R-Gsα and gpH2R-Gsα differently than the corresponding guanidines. Guanidines, AIPGs, and small H2R agonists exhibited distinct agonist properties at hH2R, gpH2R, and rH 2R measuring adenylyl cyclase activity. In contrast to ARP and IMP, AIPGs were partial H1R agonists exhibiting higher efficacies at hH1R than at gpH1R. This is remarkable because, so far, all bulky H1R agonists exhibited higher efficacies at gpH 1R than at hH1R. Collectively, our data suggest that AIPGs stabilize different active conformations in hH2R, gpH2R, and rH2R than guanidines and that, in contrast to guanidines, AIPGs are capable of stabilizing a partially active state of hH1R.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - Apr 1 2006|
ASJC Scopus subject areas
- Molecular Medicine