G[subscript q]-protein-coupled receptors (G[subscript q]PCRs) are widely distributed in the CNS and play fundamental roles in a variety of neuronal processes. Their activation results in phosphatidylinositol 4,5-bisphosphate (PIP[subscript 2]) hydrolysis and Ca[superscript 2+] release from intracellular stores via the phospholipase C (PLC)–inositol 1,4,5-trisphosphate (IP[subscript 3]) signaling pathway. Because early G[subscript q]PCR signaling events occur at the plasma membrane of neurons, they might be influenced by changes in membrane potential. In this study, we use combined patch-clamp and imaging methods to investigate whether membrane potential changes can modulate G[subscript q]PCR signaling in neurons. Our results demonstrate that G[subscript q]PCR signaling in the human neuronal cell line SH-SY5Y and in rat cerebellar granule neurons is directly sensitive to changes in membrane potential, even in the absence of extracellular Ca[superscript 2+]. Depolarization has a bidirectional effect on G[subscript q]PCR signaling, potentiating thapsigargin-sensitive Ca[superscript 2+] responses to muscarinic receptor activation but attenuating those mediated by bradykinin receptors. The depolarization-evoked potentiation of the muscarinic signaling is graded, bipolar, non-inactivating, and with no apparent upper limit, ruling out traditional voltage-gated ion channels as the primary voltage sensors. Flash photolysis of caged IP[subscript 3]/GPIP[subscript 2] (glycerophosphoryl-myo-inositol 4,5-bisphosphate) places the voltage sensor before the level of the Ca[superscript 2+] store, and measurements using the fluorescent bioprobe eGFP–PH[subscript PLCδ] (enhanced green fluorescent protein–pleckstrin homology domain–PLCδ) directly demonstrate that voltage affects muscarinic signaling at the level of the IP[subscript 3] production pathway. The sensitivity of G[subscript q]PCR IP[subscript 3] signaling in neurons to voltage itself may represent a fundamental mechanism by which ionotropic signals can shape metabotropic receptor activity in neurons and influence processes such as synaptic plasticity in which the detection of coincident signals is crucial.Peer reviewedPublisher versio
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