BK channel

BK channels, also called MaxiK or slo1 channels, are large conductance Ca2+ and voltage-activated K+ channels, which allow K+ to leave the cytoplasm under physiological conditions when activated by membrane voltage and/or intracellular Ca2+. This results in hyperpolarization or a decrease in cell excitability. BK channels are essential for key physiological processes. They are important for controlling the contraction of smooth muscle and are also for electrical tuning of hair cells in the cochlea. BK channels are important for very high concentration (> 100 mM) behavioral effects of ethanol in the worm C. elegans. It remains to be determined if, and how much, BK channels contribute to low intoxicating doses of ethanol (legal driving limit in most US states is 17.4 mM blood alcohol).

Structure


BK channels are a prime example of modular evolutionary protein design. The pore forming α-subunit consists of:
 * 1) The K+ permeable pore domain.
 * 2) The voltage sensing domain that are found in all other voltage gated K+ channels.
 * 3) A RCK domain that is involved in regulating the K+ conductance.
 * 4) A unique N-terminal transmembrane domain that is in addition to the usually 6 transmembrane domains in voltage dependent K+ channels.
 * 5) A unique large intracellular domain that acts as a sensor for the intracellular Ca2+ concentration.

