Ca-Sensitive Potassium Channels.

The Ca ion is used ubiquitously as an intracellular signaling molecule due to its high external and low internal concentration. Many Ca-sensing ion channel proteins have evolved to receive and propagate Ca signals. Among them are the Ca-activated potassium channels, a large family of potassium channels activated by rises in cytosolic calcium in response to Ca influx via Ca-permeable channels that open during the action potential or Ca release from the endoplasmic reticulum. The Ca sensitivity of these channels allows internal Ca 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 Ca sensitivity of the two best-studied groups of Ca-sensitive potassium channels: large-conductance Ca-activated K channels, K1.1, and small/intermediate-conductance Ca-activated K channels, K2.x/K3.1.