TRPA1 channel activation regulates motility in the mouse colon

Introduction: Transient receptor potential (TRP) channels are distributed throughout the body and play an important role in shaping our neuronal response to the environment. In the gastrointestinal tract there is a growing awareness of their role in regulating sensory (1) and motor functions (2). In this study we use an in-vitro murine model of colonic peristaltic-like complexes (CPMCs) to evaluate the role of TRPA1 signalling processes in regulating colonic motility.

Methods: Experiments were performed on male CD1 mice (approx 3 m age). In vitro recordings of intraluminal pressure were used to monitor the presence of CPMCs in colonic segments. Compounds were tested for their effect on colonic motility using cumulative dosing strategies. CPMC frequency and contractile activity was monitored as previously described (3): frequency was measured by calculating the time that the colon was in a non contracting state (time in quiescence, TIQ), and contractile activity was measured by calculating CPMC amplitude. Compounds were added for 900 s, and statistical analysis was by repeat measures one-way ANOVA or Students t-test, as appropriate, on n≥4 experiments. P<0.05 was taken as significant.

Results: At rest, CPMC activity comprised of regular contractile events which propagated in an aboral direction along the length of the colon. Bath addition of the TRPA1 agonist cinnamaldehyde (CMA, 1- 100 µM) inhibited CPMC activity in a dose dependent fashion, increasing the TIQ from 543 ± 32 s (vehicle) to 619± 38 s at 10 µM CMA (n=7; p<0.01 compared to vehicle) and 646 ± 22 s at 100 µM CMA (n=7; p<0.001 compared to vehicle). This coincided with a significant decrease in CPMC amplitude from 32 ± 2 mmHg (vehicle control) to 27 ± 2 mmHg at 10 µM CMA (n=7; p<0.05 compared to vehicle) and 24.2 ± 2 mmHg at 100 µM CMA (n=7; p<0.01 compared to vehicle). L-NAME (100 µM) attenuated the inhibitory effects of CMA on CPMC frequency. In these experiments the TIQ of the colon increased from 471.8 ± 35.8 s (L-NAME alone) to 486 ± 30 s at 10 µM CMA + L-NAME (n=4; p>0.05 versus L-NAME alone) and 548 ± 22.6 s at 100 µM CMA + L-NAME (n=4; p>0.05 versus L-NAME alone). L-NAME also blocked the CMA-induced amplitude changes at both 10 µM and 100 µM CMA additions (n=4; P>0.05). Bath application of the TRPA1 antagonist HC030031 (n=4; 1- 10 µM) had no effect upon basal CPMC activity, but 3 µM HC030031 attenuated the CMA-induced inhibition of CPMC frequency. In these experiments the TIQ of the colon increased from 647.3 ± 39.5 s (HC alone) to 658 ± 28.6 s at 10 µM CMA + HC (n=4; p>0.05 versus HC alone), and 677 ± 11 s at 100 µM CMA (n=4; p>0.05 versus HC alone).

Conclusion: CMA inhibits murine colonic motility through activation of TRPA1 channels, and this is mediated through nitric oxide signalling pathways. These results also suggest that it is unlikely that the TRPA1 channel is acting as a mechanosensor, and that TRPA1-induced motor inhibition is mediated by chemical stimuli. The identity of these chemical ligands is the aim of current research.

(1) Brierley et al., (2009). Gastroenterology, 137, 2084-2095

(2) Poole et al., (2011). Gastroenterology, 141: 565- 575.

(3) Keating et al. (2010). Neurogastroenterology & Motility, 245, 299-309.