Ca²⁺-Sensitive Potassium Channels

The Ca2+ ion is used ubiquitously as an intracellular signaling molecule due to its high external and low internal concentration. Many Ca2+-sensing ion channel proteins have evolved to receive and propagate Ca2+ signals. Among them are the Ca2+-activated potassium channels, a large family of potassium channels activated by rises in cytosolic calcium in response to Ca2+ influx via Ca2+-permeable channels that open during the action potential or Ca2+ release from the endoplasmic reticulum. The Ca2+ sensitivity of these channels allows internal Ca2+ to regulate the electrical activity of the cell membrane. Activating these potassium channels controls many physiological processes, from the firing properties of neurons to the control of transmitter release. This review will discuss what is understood about the Ca2+ sensitivity of the two best-studied groups of Ca2+-sensitive potassium channels: large-conductance Ca2+-activated K+ channels, K(Ca)1.1, and small/intermediate-conductance Ca2+-activated K+ channels, K(Ca)2.x/K(Ca)3.1.