Fig. 2.
Molecular structure of the cardiac sodium channel. a Cartoon of the α-subunit (Nav1.5) and the β-subunit of the cardiac sodium channel. Nav1.5 consists of four domains (DI–DIV), each containing six transmembrane segments (S1–S6); S4 segments are positively charged and act as voltage sensors. The β-subunit consists of one single transmembrane segment. b The four domains of Nav1.5 fold around an ion-conducting pore, which is lined by the loops between the S5 and S6 segments. The expression and function of Nav1.5 is regulated by β-subunits and several directly or indirectly interacting regulatory proteins