Rapidlly inactivating voltage sensitive potassium channels are found both in neurons (A-current) and cardiac myocytes (Ito) where they are responsible of the "notch’ in phase 1 of the cardiac action potential. The channels underlying Ito in humans are principally Kv4.3 and the regional differences in expression are thought to be governed by levels of the accessory protein KChIP2. Due to their critical role in controlling the trajectory of the action potential to differing degrees in various regions of the heart, blockade of this channel could lead to increased arrhythmic risk. In cortical, hippocampal, and striatal interneurons, KChIP1 is frequently co localized with Kv4.3. This complex of human Kv4.3 and KChIP1 represents a physiologically relevant cell line.