Regulation of atrial G-protein activated (GIRK) channels by phosphatidylinositol 4,5-bisphosphate and proteinkinase C isoforms

• Applicant: Professorin Dr. Marie-Cécile Kienitz
• Subject Area: Anatomy and Physiology
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 441909735

Parasympathetic control of heart rate and cardiac excitability comprises activation of G protein-activated inwardly rectifying K+ (GIRK) channels, mainly expressed in the supraventricular tissue. Cardiac GIRK channels are activated by direct interaction of their GIRK1/GIRK4 subunits with βγ subunits of heterotrimeric G proteins upon agonist activation of appropriate Gi/o-coupled receptors. Inhibition of GIRK channels by stimulation of Gq-coupled receptors (GqPCRs) is mediated by the phospholipase C (PLC)-catalyzed depletion of PtdIns(4,5)P2 (PIP2) and/or channel phosphorylation by proteinkinase C (PKC). We intend to quantify receptor-specific differences in PIP2-depletion or receptor-dependent activation of PKC-isoforms in the native environment of adult rat atrial myocytes and to analyze receptor-specific activation of different PKC isoforms during stimulation of distinct endogenous GqPCRs. Since atrial fibrillation is associated with changes in PKC isoform expression and activity, receptor-dependent activation of a specific PKC isoform might contribute to the pathogenesis of atrial fibrillation. Furthermore, the cellular mechanisms that account for receptor-specific effects of endogenous atrial GqPCRs are rather unknown. We introduce receptor-specific differences in homologous receptor desensitization as a novel mechanism of receptor specificity. Different time courses of receptor desensitization might shape the spatiotemporal activation pattern of Gq signalling components by controlling duration and strength of the receptor signal, thus resulting in receptor-specific effector modulation. In addition, we have evidence that the receptor-specific recruitment of PKC isoforms modifies the strength of the receptor signal via a negative feedback regulation, thus shaping individual GIRK channel responses. To address the contribution of specific PKC isoforms to homologous receptor desensitization, we aim to monitor GqPCR activity by means of genetically encoded FRET-biosensors that report the activity of signalling molecules downstream Gq activation in the presence and absence of different PKC isoforms. Furthermore, monitoring homologous desensitization of phosphorylation-deficient receptor mutants shall provide detailed information about the mechanism of PKC-induced receptor desensitization. The projected experiments shall provide novel insights into the cellular mechanisms of receptor specificity that might account for the sometimes opposing regulation of cardiac activity during stimulation of endogenous GqPCRs.

• DFG Programme: Research Grants