title: Regulation of Nav1.6 and Nav1.8 peripheral nerve Na+ channels by auxiliary β-subunits.
abstract: Voltage-gated Na(+) (Na(v)) channels are composed of a pore-forming α-subunit and one or more auxiliary β-subunits. The present study investigated the regulation by the β-subunit of two Na(+) channels (Na(v)1.6 and Na(v)1.8) expressed in dorsal root ganglion (DRG) neurons. Single cell RT-PCR was used to show that Na(v)1.8, Na(v)1.6, and β(1)-β(3) subunits were widely expressed in individually harvested small-diameter DRG neurons. Coexpression experiments were used to assess the regulation of Na(v)1.6 and Na(v)1.8 by β-subunits. The β(1)-subunit induced a 2.3-fold increase in Na(+) current density and hyperpolarizing shifts in the activation (-4 mV) and steady-state inactivation (-4.7 mV) of heterologously expressed Na(v)1.8 channels. The β(4)-subunit caused more pronounced shifts in activation (-16.7 mV) and inactivation (-9.3 mV) but did not alter the current density of cells expressing Na(v)1.8 channels. The β(3)-subunit did not alter Na(v)1.8 gating but significantly reduced the current density by 31%. This contrasted with Na(v)1.6, where the β-subunits were relatively weak regulators of channel function. One notable exception was the β(4)-subunit, which induced a hyperpolarizing shift in activation (-7.6 mV) but no change in the inactivation or current density of Na(v)1.6. The β-subunits differentially regulated the expression and gating of Na(v)1.8 and Na(v)1.6. To further investigate the underlying regulatory mechanism, β-subunit chimeras containing portions of the strongly regulating β(1)-subunit and the weakly regulating β(2)-subunit were generated. Chimeras retaining the COOH-terminal domain of the β(1)-subunit produced hyperpolarizing shifts in gating and increased the current density of Na(v)1.8, similar to that observed for wild-type β(1)-subunits. The intracellular COOH-terminal domain of the β(1)-subunit appeared to play an essential role in the regulation of Na(v)1.8 expression and gating.
authors.affiliation: Centre de Recherche Université Laval Robert-Giffard, 2601 Chemin de la Canardière, Quebec City, QC, Canada.
authors.forename: Juan
authors.initials: J
authors.lastname: Zhao
authors.forename: Michael E
authors.initials: ME
authors.lastname: O'Leary
authors.forename: Mohamed
authors.initials: M
authors.lastname: Chahine
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D005727:Ganglia, Spinal / Q000378:metabolism / Q000502:physiology*; D005786:Gene Expression Regulation / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000235:genetics; D062557:NAV1.6 Voltage-Gated Sodium Channel; D062559:NAV1.8 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009475:Neurons, Afferent / Q000378:metabolism / Q000502:physiology; D010525:Peripheral Nerves / Q000378:metabolism / Q000502:physiology*; D021122:Protein Subunits / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D051381:Rats; D015222:Sodium Channels / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*
chemical_list: D062557:NAV1.6 Voltage-Gated Sodium Channel; D062559:NAV1.8 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; D021122:Protein Subunits; C568317:SCN10A protein, human; C100681:SCN8A protein, human; C568319:Scn10a protein, rat; D015222:Sodium Channels