Inhibitory Effect Of Type II MGluRs Activation On ASIC3 In Primary Sensory Neurons And Its Molecular Mechanis

Objective:Acid-sensing ion channels（ASICs）play an important role in pain associated with tissue acidification.Peripheral inhibitory group Ⅱ metabotropic glutamate receptors（mGluRs）have analgesic effects in a variety of pain conditions.Whether there is a link between ASICs and mGluRs in pain processes is still unclear.Herein,we show that the group Ⅱ mGluR agonist LY354740 inhibited acid-evoked ASIC currents and action potentials in rat dorsal root ganglia neurons.Methods:This experiment was divided into two steps.First,the whole-cell patch-clamp system was used to record the effects of LY354740 on acid-induced ASIC current and action potential on acutely isolated rat DRG neurons and cell transfected with mGluR2 and ASIC3.Intracellular dialysis was used to further explore its mechanism of the action.Then,rat paws were pre-injected with LY354740 and then the acid-induced nociceptive behaviors were observed.We also studied that whether the mGluRs antagonist LY341495 could block the effect of LY354740.Results:we show that the group Ⅱ mGluR agonist LY354740 concentration-dependent inhibited acid-evoked ASIC currents in rat dorsal root ganglia neurons.LY354740 reduced the maximum current response to protons,but it did not change the sensitivity of ASICs to protons.LY354740 inhibited ASIC currents by activating group Ⅱ mGluRs.We found that the inhibitory effect of LY354740 was blocked by intracellular application of the G_i/oprotein inhibitor pertussis toxin and the cAMP analogue 8-Br-cAMP and mimicked by the protein kinase A（PKA）inhibitor H-89.LY354740 also inhibited ASIC3 currents in CHO cells coexpressing mGluR2 and ASIC3 but not in cells expressing ASIC3 alone.In addition,intraplantar injection of LY354740 dose-dependently alleviated acid-induced nociceptive behavior in rats through local group Ⅱ mGluRs.Conclusions:these results suggested that activation of peripheral group Ⅱ mGluRs inhibited the functional activity of ASICs through a mechanism that depended on G_i/oproteins and the intracellular cAMP/PKA signaling pathway in rat dorsal root ganglia neurons.We propose that peripheral group Ⅱ mGluRs are an important therapeutic target for ASIC-mediated pain.