Large-conductance calcium-activated potassium channel (KCa1.1) (BK channel)

The Large-conductance calcium-activated potassium channel (BK channel), frequently identified as the NO-sensitive K+ channel, is a high-conductance transmembrane protein essential for regulating cellular excitability and vascular tone (UniProt Q12791). These channels are unique because they are synergistically activated by both membrane depolarization and increases in intracellular calcium concentrations (PubMed 7523957). Nitric oxide (NO) modulates BK channel activity through two primary mechanisms: indirect activation via the soluble guanylate cyclase (sGC)/cGMP/Protein Kinase G (PKG) signaling pathway and direct activation through S-nitrosylation of specific cysteine residues (PubMed 11481334). In the vascular system, the opening of these channels allows for potassium efflux, which hyperpolarizes the plasma membrane and leads to the closure of voltage-gated calcium channels, ultimately resulting in smooth muscle relaxation and vasodilation (StatPearls NBK538501). While the BK channel is the primary mediator of NO-induced hyperpolarization, other channels such as ATP-sensitive potassium (KATP) channels also exhibit sensitivity to NO in specific tissues (PubMed 8120313). Due to their central role in physiological processes, BK channels are significant therapeutic targets for conditions such as hypertension, erectile dysfunction, and respiratory disorders like asthma (PubMed 24113305). However, their broad expression across various tissues, including the central nervous system and heart, presents significant challenges for achieving therapeutic selectivity and avoiding adverse effects (PubMed 15178895).

Other names

NO-sensitive K+ channelMaxi-K channelBKCa channelSlo1KCNMA1Calcium-activated potassium channel subunit alpha-1

The mechanism involves the activation of the channel by nitric oxide, either through direct S-nitrosylation of cysteine residues or indirectly via the soluble guanylate cyclase (sGC)/cGMP/Protein Kinase G (PKG) pathway. Activation leads to an efflux of potassium ions, resulting in membrane hyperpolarization, which subsequently closes voltage-gated calcium channels and reduces intracellular calcium levels, leading to smooth muscle relaxation and decreased neuronal firing (PubMed 7523957, PubMed 11481334).