A thermoprotective role of the sodium channel β1 subunit is lost with the β1(C121W) mutation

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Abstract

Purpose:

A mutation in the β1 subunit of the voltage-gated sodium (NaV) channel, β1(C121W), causes genetic epilepsy with febrile seizures plus (GEFS+), a pediatric syndrome in which febrile seizures are the predominant phenotype. Previous studies of molecular mechanisms underlying neuronal hyperexcitability caused by this mutation were conducted at room temperature. The prevalence of seizures during febrile states in patients with GEFS+, however, suggests that the phenotypic consequence of β1(C121W) may be exacerbated by elevated temperature. We investigated the putative mechanism underlying seizure generation by the β1(C121W) mutation with elevated temperature.

Methods:

Whole-cell voltage clamp experiments were performed at 22 and 34°C using Chinese Hamster Ovary (CHO) cells expressing the α subunit of neuronal NaV channel isoform, NaV1.2. Voltage-dependent properties were recorded from CHO cells expressing either NaV1.2 alone, NaV1.2 plus wild-type (WT) β1 subunit, or NaV1.2 plus β1(C121W).

Key Findings:

Our results suggest WT β1 is protective against increased channel excitability induced by elevated temperature; protection is lost in the absence of WT β1 or with expression of β1(C121W). At 34°C, NaV1.2 + β1(C121W) channel excitability increased compared to NaV1.2 + WT β1 by the following mechanisms: decreased use-dependent inactivation, increased persistent current and window current, and delayed onset of, and accelerated recovery from, fast inactivation.

Significance:

Temperature-dependent changes found in our study are consistent with increased neuronal excitability of GEFS+ patients harboring C121W. These results suggest a novel seizure-causing mechanism for β1(C121W): increased channel excitability at elevated temperature.

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