PT - JOURNAL ARTICLE AU - Alicja J. Copik AU - Cynthia Ma AU - Alan Kosaka AU - Sunil Sahdeo AU - Andy Trane AU - Hoangdung Ho AU - Paul S. Dietrich AU - Helen Yu AU - Anthony P. D. W. Ford AU - Donald Button AU - Marcos E. Milla TI - Facilitatory Interplay in α<sub>1a</sub> and β<sub>2</sub> Adrenoceptor Function Reveals a Non-G<sub>q</sub> Signaling Mode: Implications for Diversification of Intracellular Signal Transduction AID - 10.1124/mol.108.050765 DP - 2009 Mar 01 TA - Molecular Pharmacology PG - 713--728 VI - 75 IP - 3 4099 - http://molpharm.aspetjournals.org/content/75/3/713.short 4100 - http://molpharm.aspetjournals.org/content/75/3/713.full SO - Mol Pharmacol2009 Mar 01; 75 AB - Agonist occupied α1-adrenoceptors (α1-ARs) engage several signaling pathways, including phosphatidylinositol hydrolysis, calcium mobilization, arachidonic acid release, mitogen-activated protein (MAP) kinase activation, and cAMP accumulation. The natural agonist norepinephrine (NE) activates with variable affinity and intrinsic efficacy all adrenoceptors, and in cells that coexpress α1- and β-AR subtypes, such as cardiomyocytes, this leads to coactivation of multiple downstream pathways. This may result in pathway cross-talk with significant consequences to heart physiology and pathologic state. To dissect signaling components involved specifically in α1A- and β2-AR signal interplay, we have developed a recombinant model system that mimics the levels of receptor expression observed in native cells. We followed intracellular Ca2+ mobilization to monitor in real time the activation of both Gq and Gs pathways. We found that coactivation of α1A- and β2-AR by the nonselective agonist NE or via a combination of the highly selective α1A-AR agonist A61603 and the β-selective agonist isoproterenol led to increases in Ca2+ influx from the extracellular compartment relative to stimulation with A61603 alone, with no effect on the associated transient release of Ca2+ from intracellular stores. This effect became more evident upon examination of an α1A-AR variant exhibiting a partial defect in coupling to Gq, and we attribute it to potentiation of a non Gq-pathway, uncovered by application of a combination of xestospongin C, an endoplasmic reticulum inositol 1,4,5-triphosphate receptor blocker, and 2-aminoethoxydiphenyl borate, a nonselective storeoperated Ca2+ entry channel blocker. We also found that stimulation with A61603 of a second α1A-AR variant entirely unable to signal induced no Ca2+ unless β2-AR was concomitantly activated. These results may be accounted for by the presence of α1A/β2-AR heterodimers or alternatively by specific adrenoceptor signal cross-talk resulting in distinct pharmacological behavior. Finally, our findings provide a new conceptual framework to rationalize outcomes from clinical studies targeting α- and β-adrenoceptors. The American Society for Pharmacology and Experimental Therapeutics