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Updated: Aug 18, 2026

A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators
Published on: February 20, 2018
Galphaq potentiation of adenylate cyclase type 9 activity through a Ca2+/calmodulin-dependent pathway
Medhane G Cumbay1, Val J Watts
1Purdue University, Department of Medicinal Chemistry and Molecular Pharmacology, 575 Stadium Mall Drive, West Lafayette, IN 47907-2051, USA.
Abstract:
Adenylate cyclase (EC 4.6.1.1) type 9 (AC9) activity has been shown to be inhibited by PMA activation of novel protein kinase C (nPKC) isoforms. In the current study the effect on AC9 activity of activating PKC in physiological relevant manner was examined. Contrary to the anticipated inhibitory effect of activating PKCs through Gq-coupled receptors, activation of transiently expressed Gq-coupled serotonin 5-HT2A or muscarinic M5 receptors resulted in the potentiation of isoproterenol-stimulated cyclic AMP accumulation in HEK293 cells stably expressing AC9 (HEK-AC9). Consistent with Gq-mediated activation of PKC, the addition of the PKC inhibitor bisindolylmaleimide further potentiated isoproterenol-stimulated cyclic AMP accumulation. Expression of a constitutively active mutant of Galphaq in HEK-AC9 cells also produced an enhancement in basal and isoproterenol-stimulated cyclic AMP accumulation. We also examined the role of Galphaq-mediated release of intracellular Ca2+ on the observed potentiation of AC9 activity, by depleting intracellular Ca2+ stores with thapsigargin. In Ca2+-depleted HEK-AC9 cells, activation of transiently expressed M5 receptors resulted in inhibition of isoproterenol-stimulated cyclic AMP accumulation that was blocked by bisindolylmaleimide, indicating that M5 potentiation of AC9 activity requires Ca2+. This prompted us to examine the effects of the calmodulin antagonist W7 and the Ca2+/calmodulin-dependent kinase II (CaMK II) inhibitor KN-93. Pretreating cells with W7 and KN-93 significantly inhibited M5-mediated potentiation of isoproterenol-stimulated cyclic AMP accumulation in HEK-AC9 cells, suggesting that Galphaq potentiation of AC9 activity involves Ca2+/calmodulin and CaMK II. This data provides evidence for Ca2+-mediated potentiation of AC9 activity.
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