Structure and function of cardiac sodium and potassium channels

The application of patch-clamp and molecular approaches has resulted in an increasingly refined understanding of the molecular entities underlying cardiac sodium and potassium currents. The sodium current results from expression of a single large α-subunit, whereas multiple potassium currents and potassium channel α-subunits have been identified. Recapitulation of some ion currents in heterologous expression systems requires not only expression of α-subunits but also ancillary (β) subunits. Domains common to functions such as activation, inactivation, and drug block are now being identified in α- and β-gene products. Variability in the expression or function of individual ion-channel genes is an increasingly recognized source of variability in the ion currents recorded in heart cells under physiological conditions (e.g. during development) as well as in disease.