Abstract
In the 1970s, calcium-activated potassium currents were recorded for the first time. In 10years, this Ca2+-activated potassium channel was identified in rat skeletal muscle, chromaffin cells and characterized in skeletal muscle membranes reconstituted in lipid bilayers. This calcium- and voltage-activated potassium channel, dubbed BK for “Big K” due to its large ionic conductance between 130 and 300 pS in symmetric K+. The BK channel is a tetramer where the pore-forming α subunit contains seven transmembrane segments. It has a modular architecture containing a pore domain with a highly potassium-selective filter, a voltage-sensor domain and two intracellular Ca2+ binding sites in the C-terminus. BK is found in the plasma membrane of different cell types, the inner mitochondrial membrane (mitoBK) and the nuclear envelope’s outer membrane (nBK). Like BK channels in the plasma membrane (pmBK), the open probability of mitoBK and nBK channels are regulated by Ca2+ and voltage and modulated by auxiliary subunits. BK channels share common pharmacology to toxins such as iberiotoxin, charybdotoxin, paxilline, and agonists of the benzimidazole family. However, the precise role of mitoBK and nBK remains largely unknown. To date, mitoBK has been reported to play a role in protecting the heart from ischemic injury. At the same time, pharmacology suggests that nBK has a role in regulating nuclear Ca2+, membrane potential and expression of eNOS. Here, we will discuss at the biophysical level the properties and differences of mitoBK and nBK compared to those of pmBK and their pharmacology and function.
Highlights
In the 1980s, the calcium-activated potassium channel was identified for the first time in rat skeletal muscle (Pallotta et al, 1981), chromaffin cells (Marty, 1981), and skeletal muscle membranes incorporated in lipid bilayers (Latorre et al, 1982)
Compared to the vast information available for BK channel in the plasma membrane (pmBK), one may get the impression that there is a lack of evidence for Mitochondrial BK (mitoBK) and nuclear BK channels (nBK)
There has been an increase in studies regarding their biophysical and pharmacological properties during recent years (Ohya et al, 2005; Li et al, 2014) and how these studies relate to their functional role in different cell types (Gobeil et al, 2002; Selezneva et al, 2021; Wawrzkiewicz-Jałowiecka et al, 2021)
Summary
In the 1980s, the calcium-activated potassium channel was identified for the first time in rat skeletal muscle (Pallotta et al, 1981), chromaffin cells (Marty, 1981), and skeletal muscle membranes incorporated in lipid bilayers (Latorre et al, 1982). The basic pharmacology properties of mitochondrial potassium channels like mitoKATP, mitoBK, and mitoKv1.3 are similar to their equivalents in plasma membrane from different cell types (Szewczyk et al, 2006; Laskowski et al, 2016).
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