Nav1.4

Nav1.4 is a protein that in humans is encoded by the SCN4A gene. It is a voltage-gated sodium channel that plays a crucial role in the initiation and propagation of action potentials in skeletal muscle. Mutations in this gene have been associated with several myotonic disorders and periodic paralysis syndromes.

Structure

Nav1.4 is a large, complex protein composed of four homologous domains (I-IV), each containing six transmembrane segments (S1-S6). The S4 segment of each domain acts as the voltage sensor, while the pore-forming loop between S5 and S6 is responsible for sodium ion selectivity and conductance.

Function

Nav1.4 is primarily expressed in skeletal muscle, where it is responsible for the upstroke of the action potential. This rapid depolarization allows for the propagation of electrical signals along the muscle fiber, leading to muscle contraction.

Clinical significance

Mutations in the SCN4A gene can lead to a variety of neuromuscular disorders. These include Hyperkalemic periodic paralysis, Paramyotonia congenita, and Potassium-aggravated myotonia. These conditions are characterized by episodes of muscle weakness or stiffness, often triggered by exercise, cold, or potassium intake.

See also

• Sodium channel
• Voltage-gated ion channel
• Myotonia
• Periodic paralysis

References

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