STRUCTURE AND FUNCTION OF CARDIAC SODIUM AND POTASSIUM CHANNELS

The application of patch-clamp and molecular approaches has resulted i n an increasingly refined understanding of the molecular entities unde rlying cardiac sodium and potassium currents. The sodium current resul ts from expression of a single large alpha-subunit, whereas multiple p otassium currents and potassium channel alpha-subunits have been ident ified. Recapitulation of some ion currents in heterologous expression systems requires not only expression of alpha-subunits but also ancill ary (beta) subunits. Domains common to functions such as activation, i nactivation, and drug block are now being identified in alpha- and bet a-gene products. Variability in the expression or function of individu al ion-channel genes is an increasingly recognized source of variabili ty in the ion currents recorded in heart cells under physiological con ditions (e.g. during development) as well as in disease.