Module 3: Figure K+ channel organization
Functional organization of Ca2+-sensitive K+ channels.
The closed channel (shown on the left) opens in response to membrane depolarization and/or an increase in internal Ca2+ to allow K+ to flow out of the cell at a rate of 108 ions/s. Depolarization is detected by a voltage sensor that opens the pore through an electromechanical coupling process. Ca2+ acts through binding sites located on a region called the regulator of K+ conductance to open the pore through a chemomechanical coupling process. Once these activation processes open the gated pore, K+ enters the central cavity where it gains access to the selectivity filter. The latter provides a K+-specific filter, which allows K+ to pass through with a high degree of selectivity. As K+ ions (red dots) pass through the filter, they lose their water of hydration (green dots). An animated version of this figure is available.