BK channel

BK channels (big potassium), are large conductance calcium-activated potassium channels, also known as Maxi-K, slo1, or Kca1.1. BK channels are voltage-gated potassium channels that conduct large amounts of potassium ions (K+) across the cell membrane, hence their name, big potassium. These channels can be activated (opened) by either electrical means, or by increasing Ca2+ concentrations in the cell. BK channels help regulate physiological processes, such as circadian behavioral rhythms and neuronal excitability. BK channels are also involved in many processes in the body, as it is a ubiquitous channel. They have a tetrameric structure that is composed of a transmembrane domain, voltage sensing domain, potassium channel domain, and a cytoplasmic C-terminal domain, with many X-ray structures for reference. Their function is to repolarize the membrane potential by allowing for potassium to flow outward, in response to a depolarization or increase in calcium levels. Structurally, BK channels are homologous to voltage- and ligand-gated potassium channels, having a voltage sensor and pore as the membrane-spanning domain and a cytosolic domain for the binding of intracellular calcium and magnesium. Each monomer of the channel-forming alpha subunit is the product of the KCNMA1 gene (also known as Slo1). The Slo1 subunit has three main structural domains, each with a distinct function: the voltage sensing domain (VSD) senses membrane potential across the membrane, the cytosolic domain (senses calcium concentration, Ca2+ ions), and the pore-gate domain (PGD) which opens and closes to regulate potassium permeation. The activation gate resides in the PGD, which is located at either the cytosolic side of S6 or the selectivity filter (selectivity is the preference of a channel to conduct a specific ion). The voltage sensing domain and pore-gated domain are collectively referred as the membrane-spanning domains and are formed by transmembrane segments S1-S4 and S5-S6, respectively.