ERK1/2 mitogen-activated protein kinase phosphorylates sodium channel Na_v1.7 and alters its gating properties

Na_v1.7 sodium channels can amplify weak stimuli in neurons and act as threshold channels for firing action potentials. Neurotrophic factors and pro-nociceptive cytokines that are released during development and under pathological conditions activate mitogen-activated protein kinases (MAPKs). Previous studies have shown that MAPKs can transduce developmental or pathological signals by regulating transcription factors that initiate a gene expression response, a long-term effect, and directly modulate neuronal ion channels including sodium channels, thus acutely regulating dorsal root ganglion (DRG) neuron excitability. For example, neurotrophic growth factor activates (phosphorylates) ERK1/2 MAPK (pERK1/2) in DRG neurons, an effect that has been implicated in injury-induced hyperalgesia. However, the acute effects of pERK1/2 on sodium channels are not known. We have shown previously that activated p38 MAPK (pp38) directly phosphorylates Na_v1.6 and Na_v1.8 sodium channels and regulates their current densities without altering their gating properties. We now report that acute inhibition of pERK1/2 regulates resting membrane potential and firing properties of DRG neurons.Wealso show thatpERK1phosphorylates specific residues within L1 of Na_v1.7, inhibition of pERK1/2 causes a depolarizing shift of activation and fast inactivation of Na_v1.7 without altering current density, and mutation of these L1 phosphoacceptor sites abrogates the effect of pERK1/2 on this channel. Together, these data are consistent with direct phosphorylation and modulation of Na_v1.7 by pERK1/2, which unlike the modulation of Na_v1.6 and Na_v1.8 by pp38, regulates gating properties of this channel but not its current density and contributes to the effects of MAPKs on DRG neuron excitability.