Abstract
Voltage-gated KV7 channels (KV7.1 to KV7.5) are important regulators of the cell membrane potential in detrusor smooth muscle (DSM) of the urinary bladder. This study sought to further the current knowledge of KV7 channel function at the molecular, cellular, and tissue levels in combination with pharmacological tools. We used isometric DSM tension recordings, ratiometric fluorescence Ca2+ imaging, amphotericin-B perforated patch-clamp electrophysiology, and in situ proximity ligation assay (PLA) in combination with the novel compound N-(2,4,6-trimethylphenyl)-bicyclo[2.2.1]heptane-2-carboxamide (ML213), an activator of KV7.2, KV7.4, and KV7.5 channels, to examine their physiologic roles in guinea pig DSM function. ML213 caused a concentration-dependent (0.1-30 µM) inhibition of spontaneous phasic contractions in DSM isolated strips; effects blocked by the KV7 channel inhibitor XE991 (10 µM). ML213 (0.1-30 µM) also reduced pharmacologically induced and nerve-evoked contractions in DSM strips. Consistently, ML213 (10 µM) decreased global intracellular Ca2+ concentrations in Fura-2-loaded DSM isolated strips. Perforated patch-clamp electrophysiology revealed that ML213 (10 µM) caused an increase in the amplitude of whole-cell KV7 currents. Further, in current-clamp mode of the perforated patch clamp, ML213 hyperpolarized DSM cell membrane potential in a manner reversible by washout or XE991 (10 µM), consistent with ML213 activation of KV7 channel currents. Preapplication of XE991 (10 µM) not only depolarized the DSM cells, but also blocked ML213-induced hyperpolarization, confirming ML213 selectivity for KV7 channel subtypes. In situ PLA revealed colocalization and expression of heteromeric KV7.4/KV7.5 channels in DSM isolated cells. These combined results suggest that ML213-sensitive KV7.4- and KV7.5-containing channels are essential regulators of DSM excitability and contractility.