Differential efficacy of GoSlo-SR compounds on BKα and BKαγ_1–4channels

Abstract

Large conductance, voltage and Ca activated K channels (BK channels) are abundantly expressed throughout the body and are important regulators of smooth muscle tone and neuronal excitability. Their dysfunction is implicated in various diseases including overactive bladder, hypertension and erectile dysfunction. Therefore, BK channel openers bear significant therapeutic potential to treat the above diseases. GoSlo-SR compounds were designed to be potent and efficacious BK channel openers. Although their structural activity relationships, activation in both BKα and BKαβ channels and the hypothetical mode of action of these compounds has been studied in detail in recent years, their effectiveness to open the BKαγ channels still remains unexplored. In this study, we have examined the efficacy of 3 closely related GoSlo-SR openers, GoSlo-SR-5-6 (SR-5-6), GoSlo-SR-5-44 (SR-5-44) and GoSlo-SR-5-130 (SR-5-130) using inside out patches on BKα channels coexpressed with 4 different LRRC (γ) subunits in HEK293 cells. Our data suggests that the activation effects due to SR-5-6 were not significantly affected in the presence of γ subunits. Interestingly, the effects of more efficacious BK channel opener SR-5-44 were altered by different γ subunits. In cells expressing BKα channels, the shift in V (ΔV) induced by SR-5-44 (3 μM) was -76 ± 3 mV, whereas it was significantly reduced by ∼70 % in BKαγ channels (ΔV= -23 ± 3, p < 0.001, ANOVA). In BKαγ channels the ΔV was -36 ± 1 mV, which was less than that observed in BKαγ and BKαγ channels where the ΔV was -47 ± 5 mV, and -82 ± 5 mV, respectively. Additionally, the excitatory effects of a 'β specific' BK channel opener, SR-5-130 were only partially restored in the patches containing BKαγ channels. Together this data highlights that subtle modifications in GoSlo-SR structures alter their effectiveness on BK channels with accessory γ subunits and this study might provide a scaffold for the development of more tissue specific BK channel openers.

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

“…This supports the idea that they relaxed Gracilis muscle arteries by activating both BK and K v 7 channels. This dual action of GoSlo-SR compounds on BK and K v 7.4/K v 7.5 channels is further supported by the findings made on single cells expressing these channels, that is, (a) our findings reported in the present study demonstrating that GoSlo-SR compounds produce a large stimulation of native BK currents and K v 7.4 and K v 7.5 channels and (b) previously published findings showing that GoSlo-SR compounds activate expressed as well as native BK channels (Hannigan et al, 2016;Kshatri et al, 2017;Large et al, 2015;Roy et al, 2012;Roy et al, 2014;. Incidentally, the BK channel opener NS11021 has been shown to stimulate expressed K v 7.4 channels (Bentzen et al, 2007), and BMS204352 activates both BK and K v 7 channels (Schroder, Strobaek, Olesen, & Christophersen, 2003).…”

“…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, ).…”

Ionic Channels as Potential Therapeutic Targets for Erectile Dysfunction: A Review

“…They are activated in a negative feedback mechanism to control plasmatic membrane excitability in response to membrane voltage and increased cytoplasmic Ca 2+ concentration. Its dysfunction is implicated in several diseases, including erectile dysfunction (Kshatri et al, 2017;Gururaja Rao et al, 2019).…”

The GoSlo family of BK channel activators: A no-go for γ subunits?

“…The therapeutic interest of several natural and synthetic compounds has been amply described in the literature as the basis of potential treatment strategies for epilepsy, ischemic heart disease, pulmonary disease, erectile dysfunction and bladder instability. 2,3 Among them is a series of anilinoanthraquinone analogs (the GoSlo-SR family), described as potent activators of BK channels in bladder smooth muscle cells, 4 now further characterized by Kshatri et al 5 Despite the large number of pre-clinical and basic research studies, the clinical relevance of BK channel activators remains unclear. This lack of success relays partly in the poor selectivity of the compounds to target channels at specific tissues in vivo, which may ultimately be due to their ubiquitous expression and functional diversity.…”

“…Specificity must be studied in all plausible combinations with physiological relevance. Bearing this in mind, Kshatri et al 5 explore the efficacy of the GoSlo compounds on BKag constructs. Despite their structural similarity, different variants of GoSlo show distinct effects on BKag channels.…”