ABSTRACT
Inward currents carried by either sodium or calcium ions through specific membrane channel proteins depolarize the cell during systole, while outward currents carried by potassium through other channels repolarize the cell to a negative resting potential during diastole. Five major inward currents of the heart are listed in Table 23.1, along with the associated human gene for the a subunit that forms the channel pore, and the tissues where they play a dominant role. In normal electrogene-
Name Current Gene Tissue Na+ current INa SCN5A A, HP, V L-type Ca2+ current ICa-L CAV1 N, HP T-type Ca2+ current ICa-T CAV3 A Pacemaker current If, Ih HCN N Na+/Ca2+ exchange INaCaEx NCX A, V, N? The letters under tissue indicate where the current plays a major role where A is atria, V is ventricle, HP is His-Purkinje network, N is nodal tissue (sinus and atrioventricular node). For references see general reviews,93 and more recent studies for calcium channels in human heart.120
