Receptor Species-dependent Desensitization Controls KCNQ1/KCNE1 K+ Channels as Downstream Effectors of Gq Protein-coupled Receptors.

Activation of G_q protein-coupled receptors (G_qPCRs) might induce divergent cellular responses, related to receptor-specific activation of different branches of the G_q signaling pathway. Receptor-specific desensitization provides a mechanism of effector modulation by restricting the spatiotemporal activation of signaling components downstream of G_q We quantified signaling events downstream of G_qPCR activation with FRET-based biosensors in CHO and HEK 293 cells. KCNQ1/KCNE1 channels (I_Ks) were measured as a functional readout of receptor-specific activation. Activation of muscarinic M₁ receptors (M₁-Rs) caused robust and reversible inhibition of I_Ks. In contrast, activation of α_1B-adrenergic receptors (α_1B-ARs) induced transient inhibition of I_Ks, which turned into delayed facilitation after agonist withdrawal. As a novel finding, we demonstrate that G_qPCR-specific kinetics of I_Ks modulation are determined by receptor-specific desensitization, evident at the level of Gα_q activation, phosphatidylinositol 4,5-bisphosphate (PIP₂) depletion, and diacylglycerol production. Sustained I_Ks inhibition during M₁-R stimulation is attributed to robust membrane PIP₂ depletion, whereas the rapid desensitization of α_1B-AR delimits PIP₂ reduction and augments current activation by protein kinase C Overexpression of Ca²⁺-independent did not affect the time course of α_1B-AR-induced diacylglycerol formation, excluding a contribution of duanyu1531δ to α_1B-AR desensitization. Pharmacological inhibition of Ca²⁺-dependent isoforms abolished fast α_1B receptor desensitization and augmented I_Ks reduction, but did not affect I_Ks facilitation. These data indicate a contribution of Ca²⁺-dependent to α_1B-AR desensitization, whereas I_Ks facilitation is induced by Ca²⁺-independent duanyu1531 isoforms. In contrast, neither inhibition of Ca²⁺-dependent/Ca²⁺-independent isoforms nor overexpression of duanyu1531δ induced M₁ receptor desensitization, excluding a contribution of duanyu1531 to M₁-R-induced I_Ks modulation.

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