Molecular mechanism of BK channel activation by the smooth muscle relaxant NS11021

Abstract

Large-conductance Ca2+-activated K+ channels (BK channels) are activated by cytosolic calcium and depolarized membrane potential under physiological conditions. Thus, these channels control electrical excitability in neurons and smooth muscle by gating K+ efflux and hyperpolarizing the membrane in response to Ca2+ signaling. Altered BK channel function has been linked to epilepsy, dyskinesia, and other neurological deficits in humans, making these channels a key target for drug therapies. To gain insight into mechanisms underlying pharmacological modulation of BK channel gating, here we studied mechanisms underlying activation of BK channels by the biarylthiourea derivative, NS11021, which acts as a smooth muscle relaxant. We observe that increasing NS11021 shifts the half-maximal activation voltage for BK channels toward more hyperpolarized voltages, in both the presence and nominal absence of Ca2+, suggesting that NS11021 facilitates BK channel activation primarily by a mechanism that is distinct from Ca2+ activation. 30 µM NS11021 slows the time course of BK channel deactivation at −200 mV by ∼10-fold compared with 0 µM NS11021, while having little effect on the time course of activation. This action is most pronounced at negative voltages, at which the BK channel voltage sensors are at rest. Single-channel kinetic analysis further shows that 30 µM NS11021 increases open probability by 62-fold and increases mean open time from 0.15 to 0.52 ms in the nominal absence of Ca2+ at voltages less than −60 mV, conditions in which BK voltage sensors are largely in the resting state. We could therefore account for the major activating effects of NS11021 by a scheme in which the drug primarily shifts the pore-gate equilibrium toward the open state.

Multidimensional Regulation of Cardiac Mitochondrial Potassium Channels

“…In our hands, application of higher voltage usually results in the instability of the mitoplast membrane. By contrast, recordings of the plasma membrane BK Ca are usually performed in a broader range of applied voltages [ 115 , 116 ]; therefore, some differences between the plasma and mitochondrial recordings may result from an insufficient spread of the applied voltages. Additionally, the recording conditions of mitoK channels do not fully correspond to the physiological situation since the membrane potential of fully coupled and functional mitochondria is typically in the range of approximately −150 to −200 mV and is negative on the matrix side.…”

BK-Channels: Simulador de corriente macroscópica (IBK) para la investigación y la enseñanza-aprendizaje

“…Las canalopatías del canal BK están asociadas con epilepsia, alteraciones motoras, hipertensión, incontinencia urinaria e hipoacusia (Brenner et al, 2005;Du et al, 2005). Estas características hacen del canal BK un objetivo clave para las terapias farmacológicas (Rockman et al, 2020). Activadores farmacológicos del canal BK se postulan como fármacos terapéuticos en enfermedades donde un decremento en la función del canal BK está subyacente a la enfermedad (Bentzen et al, 2014).…”

BK Channel Gating Mechanisms: Progresses Toward a Better Understanding of Variants Linked Neurological Diseases

“…Comparing to the hydrophobic gate, the alternative mechanism, the selectivity filter acting as the activation gate, is not clearly defined with computational or experimental evidence. Where is the activation gate of BK channels and how it operates are not only part of the fundamental mechanism of voltage and Ca 2+ dependent activation but also important for understanding BK channel modulation by compounds that act in the pore of BK channels, such as the QA blockers, paxilline ( Zhou et al, 2020 ), and NS11021 ( Rockman et al, 2020 ; Schewe et al, 2019 ). Some of these modulators have been excellent tools for the studies of the roles of BK channels in cellular and tissue function ( Kaczorowski and Garcia, 2016 ; Cui, 2020 ), and may serve as the lead for therapies for BK variants linked neurological diseases as described in the following sections.…”