Abstract
α1-adrenergic receptor (AR) activation is thought to be initiated by disruption of a constraining interhelical salt bridge (Porter et al., 1996). Disruption of this salt bridge is achieved through a competition for the aspartic acid residue in transmembrane domain three by the protonated amine of the endogenous ligand norepinephrine and a lysine residue in transmembrane domain seven. To further test this hypothesis, we investigated the possibility that a simple amine could mimic an important functional group of the endogenous ligand and break this α1-AR ionic constraint leading to agonism. Triethylamine (TEA) was able to generate concentration-dependent increases of soluble inositol phosphates in COS-1 cells transiently transfected with the hamster α1b-AR and in Rat-1 fibroblasts stably transfected with the human α1a-AR subtype. TEA was also able to synergistically potentiate the second messenger production by weak partial α1-AR agonists and this effect was fully inhibited by the α1-AR antagonist prazosin. However, this synergistic potentiation was not observed for full α1-AR agonists. Instead, TEA caused a parallel rightward shift of the dose-response curve, consistent with the properties of competitive antagonism. TEA specifically bound to a single population of α1-ARs with a K i of 28.7 ± 4.7 mm. In addition, the site of binding by TEA to the α1-AR is at the conserved aspartic acid residue in transmembrane domain three, which is part of the constraining salt bridge. These results indicate a direct interaction of TEA in the receptor agonist binding pocket that leads to a disruption of the constraining salt bridge, thereby initiating α1-AR activation.
Footnotes
- Received October 30, 1997.
- Accepted January 6, 1998.
-
Send reprint requests to: Dianne Perez, Ph.D., Dept. of Molecular Cardiology, The Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Ave., FF30, Cleveland, OH 44195. E-mail:perezd{at}cesmtp.ccf.org
-
This work was supported by an Established Investigator Award from the National American Heart Association (D.M.P.). It was also supported in part by National Institutes of Health Grant RO1-HL52544 (D.M.P.), an unrestricted research grant from Glaxo-Wellcome (D.M.P.), a National American Heart Association Grant-in-Aid (M.T.P.), National Institutes of Health Grant RO1-HL38120 (M.T.P.), and an American Heart Association Postdoctoral Fellowship, Northeast Ohio Affiliate (J.E.P.).
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|