Large-conductance calcium-dependent potassium channel (also known as BK channel, Maxi-K channel, BKCa channel, Slo1 channel, KCa1.1 channel) (BK channel)

The large-conductance calcium-dependent potassium channel (BK channel) is a homotetrameric ion channel that conducts potassium ions across the cell membrane in response to both membrane depolarization and increases in intracellular calcium concentration. Each subunit is encoded by the KCNMA1 (Slo1) gene. Structurally, the channel contains a voltage-sensing domain (S0–S4), a pore-forming domain (S5–S6), and a large cytosolic C-terminal region with two regulator of conductance for potassium (RCK) domains that bind calcium and magnesium. The channel can associate with auxiliary β (β1–4) and γ (γ1–4) subunits, which modulate channel gating, pharmacology, and tissue-specific functions, thus contributing to functional diversity. The BK channel is ubiquitously expressed and regulates physiological processes such as neurotransmitter release, neuronal excitability, smooth muscle contractility, and circadian rhythms. It serves as a feedback regulator of membrane potential, often reducing cellular excitability by hyperpolarizing the membrane following depolarization or calcium influx, though in some specialized contexts it may paradoxically enhance calcium-mediated processes. The channel is a recognized therapeutic target for conditions involving hyperexcitability, hypertension, and smooth muscle disorders, but its broad physiological roles and subunit-dependent pharmacology present both opportunities and challenges for drug development.

Other names

BKCa channelMaxi-K channelSlo1 channelKCa1.1 channel

Activation (opening) of the channel by membrane depolarization or increased intracellular calcium, leading to potassium efflux and membrane repolarization or hyperpolarization; Modulation by auxiliary subunits (β, γ, LINGO1) alters channel kinetics, pharmacology, and tissue-specific functions; Channel activation can provide negative feedback to limit calcium influx and transmitter release, but in some contexts (e.g., photoreceptors) may paradoxically enhance calcium currents and neurotransmitter release