Cardiac K+ Channels and Channelopathies.

The physiological heart function is controlled by a well-orchestrated interplay of different ion channels conducting Na+, Ca2+ and K+. Cardiac K+ channels are key players of cardiac repolarization counteracting depolarizating Na+ and Ca2+ currents. In contrast to Na+ and Ca2+, K+ is conducted by many different channels that differ in activation/deactivation kinetics as well as in their contribution to different phases of the action potential. Together with modulatory subunits these K+ channel α-subunits provide a wide range of repolarizing currents with specific characteristics. Moreover, due to expression differences, K+ channels strongly influence the time course of the action potentials in different heart regions. On the other hand, the variety of different K+ channels increase the number of possible disease-causing mutations. Up to now, a plethora of gain- as well as loss-of-function mutations in K+ channel forming or modulating proteins are known that cause severe congenital cardiac diseases like the long-QT-syndrome, the short-QT-syndrome, the Brugada syndrome and/or different types of atrial tachyarrhythmias. In this chapter we provide a comprehensive overview of different K+ channels in cardiac physiology and pathophysiology.