Ion channels in our cells generate the nerve impulses that enable the heart to beat, the body to move, and sensation and thought to occur. Scientists from the Salk Institute for Biological Studies have identified a tiny flexible gateway that controls the rapid-fire opening and closing of a family of ion channels through which nerve-triggering potassium ions flow in and out of cells of the body. Malfunctions in the channels leads to several human diseases, including epilepsy, cardiac arrhythmias and muscle disorders. To pinpoint the parts of the ion channel structure that are important for it to function normally, Senyon Choe, Paul Slesinger and colleagues compared two types of "Kir" channels that have a unique closure device at one end that seems to control the movement of potassium in heart cells. Using painstaking detective work involving crystallography at SSRL, molecular biology and electrophysiology, the Salk team revealed that the closure device is formed from structures called G-loops that surround the "mouth" of the ion channel on the inside of the cell membrane. The researchers suspect that the G-loop complex operates like an elastic cuff that is closed in the resting position and expands to allow potassium ions out of the cell. The findings were published in the March 1, 2005 issue of Nature Neuroscience. Kir channels are important in medicine because they appear to have crucial roles in brain seizures including epilepsy, abnormal heart beats (heart arrhythmias), hyperactivity and developmental disorders. In 2001, researchers showed that Andersen's syndrome, a rare genetic disease involving cardiac arrhythmias, muscle paralysis and abnormal growth, is triggered by a mutation in the Kir2 channel.