PT - JOURNAL ARTICLE AU - Malika Israilova AU - Takashi Tanaka AU - Fumiko Suzuki AU - Shigeru Morishima AU - Ikunobu Muramatsu TI - Pharmacological Characterization and Cross Talk of α<sub>1A</sub>- and α<sub>1B</sub>-Adrenoceptors Coexpressed in Human Embryonic Kidney 293 Cells AID - 10.1124/jpet.103.061796 DP - 2004 Apr 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 259--266 VI - 309 IP - 1 4099 - http://jpet.aspetjournals.org/content/309/1/259.short 4100 - http://jpet.aspetjournals.org/content/309/1/259.full SO - J Pharmacol Exp Ther2004 Apr 01; 309 AB - We established three human embryonic kidney (HEK) 293 cell lines stably expressing α1-adrenoceptor (AR) subtypes, one (α1A, 1B-AR) coexpressing both receptors and the other two (α1A-AR and α1B-AR) expressing each receptor in isolation. In the α1A, 1B-AR cells, both receptors were clearly distinguished by the α1A-selective ligands (-)-1(3-hydroxypropyl)-5-((2R)-2-{[2-(2,2,2-trifluoroethyl]oxy]phenyl}oxy)ethyl]amino}propyl)-2,3-dihydro-1H-indole-7-carboxamide (KMD-3213) and methoxamine, but not by the subtype-nonselective ligands prazosin and phenylephrine. In all three cell lines, phenylephrine caused a concentration-dependent increase in inositol phosphates and an increase in extracellular signal-regulated kinase 1/2 (ERK1/2) activation. However, there was a 2-fold or greater maximal response to phenylephrine and a somewhat higher agonist potency in ERK1/2 activation in the α1A,1B-AR cells, compared with the responses of cells expressing either receptor individually (α1A-AR or α1B-AR). Furthermore, the antagonistic affinities of prazosin (pKb of 10.1) and KMD-3213 (9.4) for inhibiting the phenylephrine response were intermediate between the values for inhibition in α1A-AR cells (prazosin, 9.3; KMD-3213, 10.5) and α1B-AR cells (prazosin, 11.0; KMD-3213, 8.1). The inhibitor pKb values in α1A, 1B-AR also differed from their ligand binding affinities measured in α1A-AR and α1B-AR cells. In contrast, the α1A-selective agonist methoxamine, which did not activate α1B-AR cells, stimulated either α1A,1B-AR or α1A-AR cells with a comparable potency and maximum effectiveness. Our data indicate that when coexpressed in the same cell, the activation of common pathways by individual AR receptor subtypes by a nonselective agonist can exhibit enhanced responsiveness and a distinct antagonist affinity compared with the parameters for the same receptors, when expressed alone in the same cell background. The American Society for Pharmacology and Experimental Therapeutics