Alternative splicing of Na(V)1.7 exon 5 increases the impact of the painful PEPD mutant channel I1461T.
Alternative splicing is known to alter pharmacological sensitivities, kinetics, channel distribution under pathological conditions, and developmental regulation of VGSCs. Mutations that alter channel properties in Na(V)1.7 have been genetically implicated in patients with bouts of extreme pain classified as inherited erythromelalgia (IEM) or paroxysmal extreme pain disorder (PEPD). Furthermore, patients with IEM or PEPD report differential age onsets. A recent study reported that alternative splicing of Na(V)1.7 exon 5 affects ramp current properties. Since IEM and PEPD mutations also alter Na(V)1.7 ramp current properties we speculated that alternative splicing might impact the functional consequences of IEM or PEPD mutations. We compared the effects alternative splicing has on the biophysical properties of Na(V)1.7 wild-type, IEM (I136V) and PEPD (I1461T) channels. Our major findings demonstrate that although the 5A splice variant of the IEM channel had no functional impact, the 5A splice variant of the PEPD channel significantly hyperpolarized the activation curve, slowed deactivation and closed-state inactivation, shifted the ramp current activation to more hyperpolarized potentials, and increased ramp current amplitude. We hypothesize a D1/S3-S4 charged residue difference between the 5N (Asn) and the 5A (Asp) variants within the coding region of exon 5 may contribute to shifts in channel activation and deactivation. Taken together, the additive effects observed on ramp currents from exon 5 splicing and the PEPD mutation (I1461T) are likely to impact the disease phenotype and may offer insight into how alternative splicing may affect specific intramolecular interactions critical for voltage-dependent gating.
Jarecki
Brian W
BW
Department of Pharmacology and Toxicology, Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN, USA.
Sheets
Patrick L
PL
Xiao
Yucheng
Y
Jackson
James O
JO
Cummins
Theodore R
TR
D017398:Alternative Splicing; D004594:Electrophysiology; D004916:Erythromelalgia / Q000235:genetics*; D005091:Exons; D006801:Humans; D009154:Mutation; D062556:NAV1.7 Voltage-Gated Sodium Channel; D010641:Phenotype; D015222:Sodium Channels / Q000235:genetics*; D013001:Somatoform Disorders / Q000235:genetics*
D062556:NAV1.7 Voltage-Gated Sodium Channel; C486866:SCN9A protein, human; D015222:Sodium Channels