Contactin associates with Na⁺ channels and increases their functional expression

Contactin (also known as F3, F11) is a surface glycoprotein that has significant homology with the β2 subunit of voltage-gated Na⁺ channels. Contactin and Na^- channels can be reciprocally coimmunoprecipitated from brain homogenates, indicating association within a complex. Cells cotransfected with Na⁺ channel Na_v1.2α and β1 subunits and contactin have threefold to fourfold higher peak Na⁺ currents than cells with Na_v1.2α alone, Na_v1.2/β1, Na_v1.2/contactin, or Na_v1.2/β1/β2. These cells also have a correspondingly higher saxitoxin binding, suggesting an increased Na⁺ channel surface membrane density. Coimmunoprecipitation of different subunits from cell lines shows that contactin interacts specifically with the β1 subunit. In the PNS, immunocytochemical studies show a transient colocalization of contactin and Na⁺ channels at new nodes of Ranvier forming during remyelination. In the CNS, there is a particularly high level of colocalization of Na⁺ channels and contactin at nodes both during development and in the adult. Contactin may thus significantly influence the functional expression and distribution of Na⁺ channels in neurons.