Proton block and voltage gating are potassium-dependent in the cardiac leak channel Kcnk3

Potassium leak conductances were recently revealed to exist as independent molecular entities. Here, the genomic structure, cardiac localization, and biophysical properties of a murine example are considered. Kcnk3 subunits h ave two pore-forming P domains and unique functional attributes. At steady state, Kcnk3 channels behave like open, potassium-selective, transmembrane holes that are inhibited by physiological levels of proton. With voltage st eps, Kcnk3 channels open and close in two phases, one appears to be immedia te and one is time-dependent (tau = similar to 5 ms). Both proton block and gating are potassium-sensitive; this produces an anomalous increase in out ward flux as external potassium levels rise because of decreased proton blo ck. Single Kcnk3 channels open across the physiological voltage range; henc e they are "leak" conductances; however, they open only briefly and rarely even after exposure to agents that activate other potassium channels.