Effects of the novel BK (K_Ca1.1) channel opener GoSlo‐SR‐5‐130 are dependent on the presence of BK_β subunits

Abstract

BACKGROUND AND PURPOSEGoSlo-SR compounds are efficacious BK (KCa1.1) channel openers, but little is known about their mechanism of action or effect on bladder contractility. We examined the effects of two closely related compounds on BK currents and bladder contractions. EXPERIMENTAL APPROACHA combination of electrophysiology, molecular biology and synthetic chemistry was used to examine the effects of two novel channel agonists on BK channels from bladder smooth muscle cells and in HEK cells expressing BKα alone or in combination with either β1 or β4 subunits. KEY RESULTSGoSlo-SR-5-6 shifted the voltage required for half maximal activation (V1/2) of BK channels approximately −100 mV, irrespective of the presence of regulatory β subunits. The deaminated derivative, GoSlo-SR-5-130, also shifted the activation V1/2 in smooth muscle cells by approximately −100 mV; however, this was reduced by ∼80% in HEK cells expressing only BKα subunits. When β1 or β4 subunits were co-expressed with BKα, efficacy was restored. GoSlo-SR-5-130 caused a concentration-dependent reduction in spontaneous bladder contraction amplitude and this was abolished by iberiotoxin, consistent with an effect on BK channels. CONCLUSIONS AND IMPLICATIONSGoSlo-SR-5-130 required β1 or β4 subunits to mediate its full effects, whereas GoSlo-SR-5-6 worked equally well in the absence or presence of β subunits. GoSlo-SR-5-130 inhibited spontaneous bladder contractions by activating BK channels. The novel BK channel opener, GoSlo-SR-5-130, is approximately fivefold more efficacious on BK channels with regulatory β subunits and may be a useful scaffold in the development of drugs to treat diseases such as overactive bladder.

Modulation of BK Channel Function by Auxiliary Beta and Gamma Subunits

“…Additionally, HBD2 (human β-defensin 2) could activate BK channels via interactions with Leu41 and Gln43 of the β1 extracellular loop (Liu et al, 2013). A recent report showed that the newly identified BK channel opener GoSlo-SR-5-130, but not its analogue GoSlo-SR-5-6, required the presence of β1 or β4 subunit to achieve its the maximal modulatory effects on BK channels (Large et al, 2015). …”

Molecular mechanisms underlying the effect of the novel BK channel opener GoSlo: Involvement of the S4/S5 linker and the S6 segment

“…GoSlo-SR-5-6 (GoSlo) (10 μM) shifted the voltage dependence of activation in excess of −100 mV. Although the structure-activity relationships of these compounds has been established (31,32), little is known about their mode of action on BK channels, other than GoSlo does not require the β 1 -subunit to mediate its effects (33).…”

Vasodilation of rat skeletal muscle arteries by the novel BK channel opener GoSlo is mediated by the simultaneous activation of BK and Kv7 channels

“…Although GoSlo‐SR compounds reliably activate BK channels in electrophysiological experiments, their effects on the contractility of intact smooth muscle tissues appear variable. Thus, Large et al () showed that GoSlo‐SR‐5‐130 decreased rabbit bladder spontaneous contractility but did not alter contractions in response to electrical field stimulation or carbachol application. In contrast, the closely related compound, GoSlo‐SR‐5‐6 failed to alter bladder contractility (Large et al, ).…”

“…Recently, a more efficacious family of BK channel openers called the GoSlo‐SR compounds have been developed (Roy et al, ; Roy et al, ). The efficacy of some of them has been reported to depend on the presence of BK channel regulatory β and γ‐subunits (Kshatri et al, ; Large et al, ; Webb et al, ). These compounds, in particular GoSlo‐SR‐5‐130 and GoSlo‐SR‐5‐6,activated BK channels in freshly isolated smooth muscle cells from rabbit bladder (Large et al, ), rabbit corpus cavernosum (Hannigan et al, ), and bronchial smooth muscle (Bradley et al, ).…”

“…The efficacy of some of them has been reported to depend on the presence of BK channel regulatory β and γ‐subunits (Kshatri et al, ; Large et al, ; Webb et al, ). These compounds, in particular GoSlo‐SR‐5‐130 and GoSlo‐SR‐5‐6,activated BK channels in freshly isolated smooth muscle cells from rabbit bladder (Large et al, ), rabbit corpus cavernosum (Hannigan et al, ), and bronchial smooth muscle (Bradley et al, ). Furthermore, Webb et al () demonstrated that the effects of GoSlo‐SR‐5‐6 were reduced by >80%, when a triplet of mutations were introduced on the S4/S5 linker and S6 helix.…”