Voltage Dependence of Prostanoid Receptors

Abstract

G protein-coupled receptors (GPCRs) are the largest class of transmembrane receptors and serve as signal mediators to transduce information from extracellular signals such as neurotransmitters, hormones, or drugs to cellular responses. They are exposed to the strong electrical field of the plasma membrane. In the last decade voltage modulation of ligand-induced GPCR activity has been reported for several GPCRs. Using Foerster resonance energy transfer-based biosensors in patch clamp experiments, we discovered a robust voltage dependence of the thromboxane receptor (TP receptor) on the receptor level as well as on downstream signaling. TP receptor activity doubled upon depolarization from -90 to +60 mV in the presence of U46619, a stable analog of prostaglandin H₂ Half-maximal effective potential (V_0.5) determined for TP receptor was -46 mV, which is within the physiologic range. We identified that depolarization affected the agonist affinity for the TP receptor. Depolarization enhanced responses of several structural analogs of U46619 with modifications to a similar extent all around the molecule, indicating that voltage modulates the general conformation of TP receptor. By means of site direct mutagenesis, we identified TP receptor R295^7.40, which showed alteration of voltage sensitivity of TP receptor upon mutation. Voltage sensitivity was not limited to TP receptor because prostaglandin F receptor activated with U46619 and prostaglandin E₂ receptor subtype 3 activated with iloprost showed a similar reaction to depolarization as TP receptor. However, prostacyclin receptor activated with iloprost showed no detectable voltage dependence. SIGNIFICANCE STATEMENT: Prostanoids mediate many of their physiological effects via transmembrane receptors expressed in the plasma membrane of excitable cells. We found that agonist-mediated activation of prostaglandin F receptors and prostaglandin E₂ receptors as well as thromboxane receptors are activated upon depolarization, whereas prostacyclin receptors are not. The voltage-induced modulation of thromboxane receptor activity was observed on the level of receptor conformation and downstream signaling. The range of voltage dependence was restricted by R295^7.40 in the agonist-binding pocket.