Dataset Information

Mice with an NaV1.4 sodium channel null allele have latent myasthenia, without susceptibility to periodic paralysis.

ABSTRACT: Over 60 mutations of SCN4A encoding the NaV1.4 sodium channel of skeletal muscle have been identified in patients with myotonia, periodic paralysis, myasthenia, or congenital myopathy. Most mutations are missense with gain-of-function defects that cause susceptibility to myotonia or periodic paralysis. Loss-of-function from enhanced inactivation or null alleles is rare and has been associated with myasthenia and congenital myopathy, while a mix of loss and gain of function changes has an uncertain relation to hypokalaemic periodic paralysis. To better define the functional consequences for a loss-of-function, we generated NaV1.4 null mice by deletion of exon 12. Heterozygous null mice have latent myasthenia and a right shift of the force-stimulus relation, without evidence of periodic paralysis. Sodium current density was half that of wild-type muscle and no compensation by retained expression of the foetal NaV1.5 isoform was detected. Mice null for NaV1.4 did not survive beyond the second postnatal day. This mouse model shows remarkable preservation of muscle function and viability for haploinsufficiency of NaV1.4, as has been reported in humans, with a propensity for pseudo-myasthenia caused by a marginal Na(+) current density to support sustained high-frequency action potentials in muscle.

SUBMITTER: Wu F

PROVIDER: S-EPMC4892753 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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Mice with an NaV1.4 sodium channel null allele have latent myasthenia, without susceptibility to periodic paralysis.

Wu Fenfen F Mi Wentao W Fu Yu Y Struyk Arie A Cannon Stephen C SC

Brain : a journal of neurology 20160405 Pt 6

Over 60 mutations of SCN4A encoding the NaV1.4 sodium channel of skeletal muscle have been identified in patients with myotonia, periodic paralysis, myasthenia, or congenital myopathy. Most mutations are missense with gain-of-function defects that cause susceptibility to myotonia or periodic paralysis. Loss-of-function from enhanced inactivation or null alleles is rare and has been associated with myasthenia and congenital myopathy, while a mix of loss and gain of function changes has an uncerta ...[more]

PMID: 27048647

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Project description:Hypokalaemic periodic paralysis is typically associated with mutations of voltage sensor residues in calcium or sodium channels of skeletal muscle. To date, causative sodium channel mutations have been studied only for the two outermost arginine residues in S4 voltage sensor segments of domains I to III. These mutations produce depolarization of skeletal muscle fibres in response to reduced extracellular potassium, owing to an inward cation-selective gating pore current activated by hyperpolarization. Here, we describe mutations of the third arginine, R3, in the domain III voltage sensor i.e. an R1135H mutation which was found in two patients in separate families and a novel R1135C mutation identified in a third patient in another family. Muscle fibres from a patient harbouring the R1135H mutation showed increased depolarization tendency at normal and reduced extracellular potassium compatible with the diagnosis. Additionally, amplitude and rise time of action potentials were reduced compared with controls, even for holding potentials at which all NaV1.4 are fully recovered from inactivation. These findings may be because of an outward omega current activated at positive potentials. Expression of R1135H/C in mammalian cells indicates further gating defects that include significantly enhanced entry into inactivation and prolonged recovery that may additionally contribute to action potential inhibition at the physiological resting potential. After S4 immobilization in the outward position, mutant channels produce an inward omega current that most likely depolarizes the resting potential and produces the hypokalaemia-induced weakness. Gating current recordings reveal that mutations at R3 inhibit S4 deactivation before recovery, and molecular dynamics simulations suggest that this defect is caused by disrupted interactions of domain III S2 countercharges with S4 arginines R2 to R4 during repolarization of the membrane. This work reveals a novel mechanism of disrupted S4 translocation for hypokalaemic periodic paralysis mutations at arginine residues located below the gating pore constriction of the voltage sensor module.

Dataset Information

Mice with an NaV1.4 sodium channel null allele have latent myasthenia, without susceptibility to periodic paralysis.

Publications

Mice with an NaV1.4 sodium channel null allele have latent myasthenia, without susceptibility to periodic paralysis.

Similar Datasets

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