Kv7 channel regulation of colonic motility in mice

Introduction: Kv7 channels are voltage-gated potassium channels that have wide ranging effects upon many cell types. Kv7 channels have been identified in murine colonic smooth muscle suggesting they play a role in regulating motility (Jepps et al., 2009), and in this study we provide evidence that Kv7 channels regulate colonic motility-like behaviour. Methods: Experiments were performed on young adult C57BL/6 mice. In vitro recordings of intraluminal pressure were used to monitor the presence of colonic peristaltic motor complexes (CPMCs) in colonic segments using a Trendelenburg-type preparation. Colonic motility-like behaviour was quantified using changes in CPMC frequency, time in quiescence (TIQ, a measure of non-motor activity) and amplitude as previously described (Keating et al., 2014). Compounds were tested for their effect on colonic motility using a cumulative dosing strategy. Statistical analysis was by one-way ANOVA on n≥4 experiments. P<0.05 was taken as significant. Results: Luminal infusion of Krebs solution into colonic segments initiated CPMC activity that persisted for approximately 4 h. Bath application of the Kv7 channel opener retigabine significantly decreased CPMC frequency from 9±0.6 CPMCs/900 s (vehicle) to 1.6±0.2 CPMCs/900 s (1µM retigabine, p<0.001 versus vehicle). Retigabine increased TIQ from 589±20 s (vehicle) to 639±20.7 s (0.3 µM retigabine, p<0.05 versus vehicle) and 841±9 s (1µM retigabine, p<0.001 versus vehicle). Retigabine had a more potent inhibitory effect upon CPMC amplitude than CPMC frequency and TIQ: 0.1 µM retigabine significantly decreased amplitude from 25.0±2.4 mmHg (vehicle) to 18.9±1.6 mmHg (retigabine, p<0.001 versus vehicle). Bath application of the Kv7 channel blocker XE991 significantly increased CPMC frequency from 9.8±0.8 CPMC/900 (vehicle) to 14.5±1.8 CPMC/900 s at 1 µM XE991 (p<0.001 versus vehicle). XE991 decreased TIQ from 592.8±20.6 s (vehicle) to 464±32.1 s (0.3 µM XE991, p<0.001 versus vehicle) and 471±21.1 s (1 µM XE991, p<0.001 versus vehicle). XE991 significantly increased CPMC amplitude from 17.2±2.5 mmHg (vehicle) to 23.2±1.7 mmHg, (0.3 µM XE991, p<0.01 versus vehicle). Conclusion: We found that pharmacological modulation of Kv7 channels on murine smooth muscle regulated colonic motility. Opening of Kv7 channels attenuated motility, whereas their blockade augmented motility. Consequently targeting Kv7 channels may have therapeutic implications for motility disorders of the gut.