Abstract
OBJECTIVE: Our recent studies have demonstrated voltage-gated KCNQ channels (KCNQ1-KCNQ5) as key regulators of detrusor smooth muscle (DSM) function. Despite emerging developments, the physiological role of individual KCNQ channel subtypes remains less clear. Here, we utilized the novel compound ML-213, a potent activator of KCNQ2, KCNQ4, and KCNQ5 channels, to elucidate their physiological roles in guinea pig DSM function. METHODS: Using isometric DSM tension recordings, Ca(2+) imaging, and amphotericin-B perforated patch-clamp electrophysiology, we elucidated the role of ML-213-sensitive KCNQ channels in regulating DSM excitability and contractility. RESULTS: ML-213 concentration-dependently (100 nM–30 µM) inhibited spontaneous phasic, pharmacologically-induced, and nerve-evoked contractions in DSM isolated strips. ML-213 (10 µM) decreased the global intracellular Ca(2+) concentrations in DSM isolated strips, effects blocked by the L-type voltage-gated Ca(2+) (Ca(V)) channel inhibitor nifedipine (1 µM) and the KCNQ1-KCNQ5 channel inhibitor XE991 (10 µM). These data suggest that ML-213 decreases the global intracellular Ca(2+) concentration by inhibiting L-type Ca(V) channels through an indirect mechanism downstream from KCNQ channel activation. In addition, ML-213 hyperpolarized the cell membrane potential and inhibited spontaneous action potentials in DSM cells, effects reversible by washout. We next aimed to examine the effects of ML-213 on whole cell KCNQ currents. To isolate KCNQ currents, the bath solution contained the large conductance voltage- and Ca(2+)-activated K(+) channel inhibitor paxilline (1 µM) and gadolinium chloride (GdCl(3), 50 µM), which blocks L-type Ca(V) channels and non-selective cation channels. Under these experimental conditions, ML-213 (10 µM) enhanced whole cell KCNQ currents. These findings suggest that the modulation of K(+) transport through ML-213-sensitive KCNQ channels underlies ML-213-induced cell membrane hyperpolarization to decrease the global intracellular Ca(2+) concentration and DSM contractility. CONCLUSIONS: These data using the novel compound ML-213, suggest that KCNQ2-, KCNQ4-, and KCNQ5-containing channels are essential regulators of the excitability, intracellular Ca(2+) concentration, and contractility of DSM by virtue of their control of the membrane potential. Moreover, these new findings provide a foundational basis for future investigations on KCNQ channel functional roles in human DSM excitability and contractility to confirm their potential as novel therapeutic targets for overactive bladder. SOURCE OF FUNDING: NIH grant R01-DK106964 to GV Petkov and F31-DK104528 to A Provence.