Functional Analysis of a Voltage‐Gated Sodium Channel and Its Splice Variant from Rat Dorsal Root Ganglia

Abstract

Neurons of the dorsal root ganglia (DRG) express a diversity of voltage‐gated sodium channels. From rat DRG we have cloned and functionally expressed a tetrodotoxin‐sensitive sodium channel α subunit, NaCh6/Scn8a/rPN4, and a splice variant, rPN4a. Primary structure analysis shows NaCh6/Scn8a/rPN4 to be highly homologous (99%) to NaCh6 and most likely represents the same transcript. The splice variation in rPN4a is homologous in sequence and location to that of rat brain I. Tissue distribution analyzed by RT‐PCR showed NaCh6/Scn8a/rPN4 to be expressed at its highest levels in rat brain, at moderate levels in spinal cord, and at lower levels in DRG, nodose ganglia, and superior cervical ganglia and to be absent from sciatic nerve, heart, and skeletal muscle. In contrast, rPN4a shows no expression in brain and low‐level expression in spinal cord, whereas in DRG its expression is comparable to that of NaCh6/Scn8a/rPN4. Functional analysis of these channels expressed in Xenopus oocytes showed that NaCh6/Scn8a/rPN4 and rPN4a exhibited similar properties, with V1/2≅−100 mV for steady‐state inactivation and V1/2≅−40 mV for activation. rPN4a recovered from inactivation significantly faster than NaCh6/Scn8a/rPN4. NaCh6/Scn8a/rPN4 was inhibited by tetrodotoxin with an IC50≅ 1 nM. Coexpression of the β1 subunit accelerated inactivation kinetics, but the β2 subunit was without effect.

Developmental Changes in Two Voltage-Dependent Sodium Currents in Utricular Hair Cells

“…We estimated a K D of 16 nM for I Na,2 , which falls in the range of values for diverse TTX-sensitive Na ϩ currents in other cell types (1-25 nM) (Chen et al 2000;Dietrich et al 1998;Moran et al 2003;Noda et al 1986;Sangameswaran et al 1997;Smith et al 1998;Smith and Goldin 1998). mRNA for Na V 1.1, Na V 1.2, Na V 1.3, Na V 1.6, and Na V 1.7 has been detected previously in P1 rat utricles (Chabbert et al 2003;Mechaly et al 2005) and our RT-PCR results generally agreed with these findings.…”

Distribution of voltage-gated sodium channel ?-subunit and ?-subunit mRNAs in human hippocampal formation, cortex, and cerebellum

“…In addition, expression patterns are modified by different pathologic conditions in rat (Willow et al, 1986;Bartolomei et al, 1997;Gastaldi et al, 1997Gastaldi et al, , 1998) and human (Lombardo et al, 1996). Studies in rat and human also indicate that channel diversity is modified extensively by mRNA splicing (Auld et al, 1988;Sarao et al, 1991;Schaller et al, 1992;Gustafson et al, 1993;Plummer et al, 1997;Dietrich et al, 1998;Lu and Brown, 1998;Oh and Waxman, 1998). In vitro studies indicate that posttranslational modifications of sodium channel proteins may include phosphorylation by cAMP-dependent protein kinase A and protein kinase C (Numann et al, 1991;Li et al, 1992) and interaction with G ␤␥ subunits (Ma et al, 1997).…”

Fibroblast Growth Factor Homologous Factor 2B: Association with Nav1.6 and Selective Colocalization at Nodes of Ranvier of Dorsal Root Axons

“…Na v 1.6 produces a fast inactivating, TTX-sensitive (TTX-S) sodium current (Dietrich et al, 1998;Smith et al, 1998;Herzog et al, 2003b). Disruption in mice of Scn8a, the gene that encodes Na v 1.6, produces the motor endplate disease (med) resulting in juvenile lethality (Burgess et al, 1995), whereas several point mutations produce less severe neurological disorders (Meisler et al, 2002).…”