Potentiation of acid-sensing ion channel activity by peripheral group I metabotropic glutamate receptor signaling

Abstract

Glutamate activates peripheral group I metabotropic glutamate receptors (mGluRs) and contributes to inflammatory pain. However, it is still not clear the mechanisms are involved in group I mGluR-mediated peripheral sensitization. Herein, we report that group I mGluRs signaling sensitizes acid-sensing ion channels (ASICs) in dorsal root ganglion (DRG) neurons and contributes to acidosis-evoked pain. DHPG, a selective group I mGluR agonist, can potentiate the functional activity of ASICs, which mediated the proton-induced events. DHPG concentration-dependently increased proton-gated currents in DRG neurons. It shifted the proton concentration-response curve upwards, with a 47.3±7.0% increase of the maximal current response to proton. Group I mGluRs, especially mGluR5, mediated the potentiation of DHPG via an intracellular cascade. DHPG potentiation of proton-gated currents disappeared after inhibition of intracellular Gq/11 proteins, PLCβ, PKC or PICK1 signaling. Moreover, DHPG enhanced proton-evoked membrane excitability of rat DRG neurons and increased the amplitude of the depolarization and the number of spikes induced by acid stimuli. Finally, peripherally administration of DHPG dose-dependently exacerbated nociceptive responses to intraplantar injection of acetic acid in rats. Potentiation of ASIC activity by group I mGluR signaling in rat DRG neurons revealed a novel peripheral mechanism underlying group I mGluRs involvement in hyperalgesia.

Keywords: Acid-sensing ion channel; Dorsal root ganglion neuron; Group I metabotropic glutamate receptor; Neuronal excitability; Pain; Proton-gated current.