Voltage-gated sodium channel alpha-subunit extracellular site 3 (NaV site 3)

The term "Other NaV channel alpha-subunits, extracellular site 3" refers to the neurotoxin receptor site 3 found across the various isoforms of the voltage-gated sodium channel (NaV) family, including NaV1.1 through NaV1.9 (Alexander et al., 2021). These alpha-subunits are large transmembrane proteins that form the ion-conducting pore and are essential for the generation and propagation of action potentials in neurons, cardiomyocytes, and skeletal muscle cells (Catterall, 2012). Extracellular site 3 is specifically located on the S3-S4 loop of domain IV and serves as the binding target for alpha-scorpion toxins and sea anemone toxins (Stevens et al., 2011). Binding at this site impairs the voltage-sensing mechanism of domain IV, which is coupled to the fast inactivation process, thereby slowing channel closure and causing persistent sodium influx (Gordon et al., 1996). This prolonged activation leads to cellular hyperexcitability, which is a hallmark of various channelopathies, including epilepsy, chronic pain syndromes, and cardiac arrhythmias (Catterall, 2012). While site 3 is primarily used as a pharmacological tool to study channel gating, it represents a potential target for developing modulators that can fine-tune excitability in specific tissues (Stevens et al., 2011).

Other names

Neurotoxin receptor site 3Alpha-scorpion toxin binding siteSea anemone toxin binding siteNaV extracellular site 3Voltage-gated sodium channel site 3

Binding to the extracellular S3-S4 loop of domain IV slows the inactivation of the sodium channel, prolonging the inward sodium current and increasing membrane excitability.