Inhibition of TRPC4 Channel Activity in Colonic Myocytes by Tricyclic Antidepressants Disrupts Colonic Motility Causing Constipation

Abstract Background: Tricyclic antidepressants (TCAs) have been used to treat depression and were recently approved for treating irritable bowel syndrome (IBS) patients with severe or refractory IBS symptoms. However, the molecular mechanism of TCA action in the gastrointestinal (GI) tract remains poorly understood. Transient receptor potential channel canonical type 4 (TRPC4), which is a Ca2+-permeable nonselective cation channel, is a critical regulator of GI excitability. Herein, we investigated whether TCA modulates TRPC4 channel activity and by what mechanism in colonic myocytes consequently causes constipation.Methods: To prove the clinical benefit in patients with diarrhea by TCA treatment, we performed mechanical tension recording using human colonic migrating motor complexes (CMMCs) and isolated muscle strips. To determine the contribution of TRPC4 to colonic motility, we measured the electrical activity of heterologous or endogenous TRPC4 by TCAs using the patch clamp technique in HEK293 cells and murine colonic myocytes.Results: All TCA compounds significantly inhibited the spontaneous contraction of CMMCs and muscle strips isolated from CMMCs by TRPC4 inhibition of colonic myocytes. In TRPC4-overexpressed HEK cells, we observed TCA-evoked direct inhibition of TRPC4 with IC50 values. Compared with TRPC4-knockout mice, we identified that muscarinic cationic current (mIcat) was suppressed through TRPC4 inhibition by TCA in isolated murine colonic myocytes. Conclusions: We investigated the inhibitory effect of the TRPC4 current by TCAs on colonic motility in TCA-induced constipation. These findings provide clinical insights into abnormal intestinal motility and medical interventions aimed at IBS therapy.