title: Modulation of Nav1.7 and Nav1.8 peripheral nerve sodium channels by protein kinase A and protein kinase C.
abstract: 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 Nav1.7 (TTX-sensitive) and Nav1.8 (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 Nav1.8 currents and an attenuation of Nav1.7 currents. PKA-induced increases (Nav1.8) and decreases (Nav1.7) in peak currents were not associated with shifts in voltage-dependent activation or inactivation. The PKA-mediated increase in Nav1.8 current amplitude was prevented by chloroquine, suggesting that cell trafficking may contribute to the changes in Nav1.8 current amplitudes. A dose-dependent decrease in Nav1.7 and Nav1.8 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 Nav1.7 and Nav1.8 channels by 6.5 and 14 mV, respectively, in the depolarizing direction. The role of individual PKC isozymes in the regulation of Nav1.7 and Nav1.8 was determined using PKC-isozyme-specific peptide activators and inhibitors. The decrease in the Nav1.8 peak current induced by PMA was prevented by a specific epsilonPKC isozyme peptide antagonist, whereas the PMA effect on Nav1.7 was prevented by epsilonPKC and betaIIPKC peptide inhibitors. The data showed that Nav1.7 and Nav1.8 were differentially modulated by PKA and PKC. This is the first report demonstrating a functional role for epsilonPKC and betaIIPKC in the regulation of Nav1.7 and Nav1.8 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.
authors.affiliation: Laval University, Department of Medicine, Sainte Foy, Quebec, G1V 4G5, Canada.
authors.forename: Kausalia
authors.initials: K
authors.lastname: Vijayaragavan
authors.forename: Mohamed
authors.initials: M
authors.lastname: Boutjdir
authors.forename: Mohamed
authors.initials: M
authors.lastname: Chahine
mesh_terms: D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004553:Electric Conductivity; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology / Q000378:metabolism*; D007527:Isoenzymes / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D062556:NAV1.7 Voltage-Gated Sodium Channel; D062559:NAV1.8 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects; D009865:Oocytes; D018408:Patch-Clamp Techniques / Q000379:methods; D010455:Peptides / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D015222:Sodium Channels / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014981:Xenopus
chemical_list: D004791:Enzyme Inhibitors; D007527:Isoenzymes; D062556:NAV1.7 Voltage-Gated Sodium Channel; D062559:NAV1.8 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; D010455:Peptides; C568319:Scn10a protein, rat; C503480:Scn9a protein, rat; D015222:Sodium Channels; D005576:Colforsin; D013779:Tetrodotoxin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C