Modulation of Nav1.7 and Nav1.8 peripheral nerve sodium channels by protein kinase A and protein kinase C

Voltage-gated Na+ channels (VGSC) are transmembrane proteins that are essential for the initiation and propagation of action potentials in neuronal excitability. Because neurons express a mixture of Na+ channel isoforms and protein kinase C (PKC) isozymes, the nature of which channel is being regulated by which PKC isozyme is not known. We showed that DRG VGSC Na-v 1.7 (TTX-sensitive) and Na-v 1.8 (TTX-resistant), expressed in Xenopus oocytes were differentially regulated by protein kinase A (PKA) and PKC isozymes using the two-electrode voltage-clamp method. PKA activation resulted in a dose-dependent potentiation of Na-v 1.8 currents and an attenuation of Na-v 1.7 currents. PKA-induced increases ( Na-v 1.8) and decreases (Na-v 1.7) in peak currents were not associated with shifts in voltage-dependent activation or inactivation. The PKA-mediated increase in Na-v 1.8 current amplitude was prevented by chloroquine, suggesting that cell trafficking may contribute to the changes in Na-v 1.8 current amplitudes. A dose-dependent decrease in Na-v 1.7 and Na-v 1.8 currents was observed with the PKC activators phorbol 12-myristate, 13-acetate (PMA) and phorbol 12,13-dibutyrate. PMA induced shifts in the steady-state activation of Na-v 1.7 and Na v 1.8 channels by 6.5 and 14 mV, respectively, in the depolarizing direction. The role of individual PKC isozymes in the regulation of Na-v 1.7 and Na-v 1.8 was determined using PKC-isozyme-specific peptide activators and inhibitors. The decrease in the Na-v 1.8 peak current induced by PMA was prevented by a specific epsilonPKC isozyme peptide antagonist, whereas the PMA effect on Na v 1.7 was prevented by epsilonPKC and betaIIPKC peptide inhibitors. The data showed that Na-v 1.7 and Na v 1.8 were differentially modulated by PKA and PKC. This is the first report demonstrating a functional role for epsilonPKC and betaIIPKC in the regulation of Na-v 1.7 and Na-v 1.8 Na+ channels. Identification of the particular PKC isozymes(s) that mediate the regulation of Na+ channels is essential for understanding the molecular mechanism involved in neuronal ion channel regulation in normal and pathological conditions.