A novel cardiac potassium channel that is active and conductive at depolarized potentials

We report the existence of a novel potassium channel revealed in single-channel recordings from guinea-pig ventricular heart cells. The channel, observed in ∼10% of patches, demonstrates a 14 pS conductance at physiological potassium concentrations, does not rectify over the voltage range of the action potential, and is quite selective for K ions. The channel activates with depolarization, but does not require intracellular Ca²⁺ ions to open. Open channel probability increases rapidly (<10 ms) to a plateau in response to depolarizing voltage steps, and demonstrates no detectable inactivation (>600 ms). These features clearly distinguish this channel from other known K channels in cardiac muscle. Because of its high activity at plateau potentials, we propose the name i_Kp.