The agonism and synergistic potentiation of weak partial agonists by triethylamine in α1-adrenergic receptor activation:: Evidence for a salt bridge as the initiating process

被引:6
作者
Porter, JE
Edelmann, SE
Waugh, DJ
Piascik, MT
Perez, DM
机构
[1] Cleveland Clin Fdn, Lerner Res Inst, Dept Mol Cardiol, Cleveland, OH 44195 USA
[2] Univ Kentucky, Coll Med, Dept Pharmacol, Lexington, KY 40536 USA
关键词
D O I
10.1124/mol.53.4.766
中图分类号
R9 [药学];
学科分类号
1007 ;
摘要
alpha(1)-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 alpha(1)-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 alpha(1b)-AR and in Rat-1 fibroblasts stably transfected with the human alpha(1a)-AR subtype. TEA was also able to synergistically potentiate the second messenger production by weak partial alpha(1)-AR agonists and this effect was fully inhibited by the alpha(1)-AR antagonist prazosin. However, this synergistic potentiation was not observed for full alpha(1)-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 alpha(1)-ARs with a K-i of 28.7 +/- 4.7 mM. In addition, the site of binding by TEA to the alpha(1)-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 alpha(1)-AR activation.
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页码:766 / 771
页数:6
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