@article {Copik713, author = {Alicja J. Copik and Cynthia Ma and Alan Kosaka and Sunil Sahdeo and Andy Trane and Hoangdung Ho and Paul S. Dietrich and Helen Yu and Anthony P. D. W. Ford and Donald Button and Marcos E. Milla}, title = {Facilitatory Interplay in α1a and β2 Adrenoceptor Function Reveals a Non-Gq Signaling Mode: Implications for Diversification of Intracellular Signal Transduction}, volume = {75}, number = {3}, pages = {713--728}, year = {2009}, doi = {10.1124/mol.108.050765}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {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}, issn = {0026-895X}, URL = {https://molpharm.aspetjournals.org/content/75/3/713}, eprint = {https://molpharm.aspetjournals.org/content/75/3/713.full.pdf}, journal = {Molecular Pharmacology} }