Receptor-species dependent desensitization controls KCNQ1/KCNE1 K+ channels as downstream effectors of Gq protein-coupled receptors

Abstract Activation of Gq protein−coupled receptors (GqPCRs) might induce divergent cellular responses, related to receptor−specific activation of different branches of the Gq−signaling pathway. Receptor−specific desensitization provides a mechanism of effector modulation by restricting the spatiotemporal activation of signaling components downstream of Gq. We quantified signaling events downstream to GqPCR activation with Foerster resonance energy transfer (FRET)−based biosensors in CHO and HEK 293 cells. KCNQ1/KCNE1 channels (IKs) were measured as a functional readout of receptor−specific activation. Activation of muscarinic M1−receptors (M1−R) caused robust and reversible inhibition of IKs. In contrast, activation of α1B−adrenergic receptors (α1B−AR) induced transient inhibition of IKs, which turned into delayed facilitation after agonist withdrawal. As a novel finding, we demonstrate that GqPCR−specific kinetics of IKs modulation are determined by receptor−specific desensitization, evident at the level of Gαq−activation, phosphatidylinositol 4,5−bisphosphate (PIP2)−depletion and diacylglycerol (DAG) production. Sustained IKs inhibition during M1−R stimulation is attributed to robust membrane PIP2−depletion, whereas the rapid desensitization of α1B−AR delimits PIP2−reduction and augments current activation by protein kinase C (PKC). Overexpression of Ca2+−independent PKCδ did not affect the time course of α1B-AR−induced DAG formation, excluding a contribution of PKCδ to α1B−AR desensitization. Pharmacological inhibition of Ca2+-dependent PKC−isoforms abolished fast α1B−receptor desensitization and augmented IKs reduction, but did not affect IKs facilitation. These data indicate a contribution of Ca2+-dependent PKCs to α1B-AR−desensitization, whereas IKs facilitation is induced by Ca2+−independent PKC isoforms. In contrast, neither inhibition of Ca2+−dependent/Ca2+−independent isoforms nor overexpression of PKCδ induced M1−receptor desensitization, excluding a contribution of PKC to M1−R-induced IKs modulation.