Excitatory cholinergic responses in mouse colon intramuscular interstitial cells of Cajal are due to enhanced Ca release via M receptor activation.

Colonic intramuscular interstitial cells of Cajal (ICC-IM) are associated with cholinergic varicosities, suggesting a role in mediating excitatory neurotransmission. Ca release in ICC-IM activates Ano1, a Ca -activated Cl conductance, causing tissue depolarization and increased smooth muscle excitability. We employed Ca imaging of colonic ICC-IM in situ, using mice expressing GCaMP6f in ICC to evaluate ICC-IM responses to excitatory neurotransmission. Expression of muscarinic type 2, 3 (M , M ), and NK receptors were enriched in ICC-IM. NK receptor agonists had minimal effects on ICC-IM, whereas neostigmine and carbachol increased Ca transients. These effects were reversed by DAU 5884 (M receptor antagonist) but not AF-DX 116 (M receptor antagonist). Electrical field stimulation (EFS) in the presence of L-NNA and MRS 2500 enhanced ICC-IM Ca transients. Responses were blocked by atropine or DAU 5884, but not AF-DX 116. ICC-IM responses to EFS were ablated by inhibiting Ca stores with cyclopiazonic acid and reduced by inhibiting Ca influx via Orai channels. Contractions induced by EFS were reduced by an Ano1 channel antagonist, abolished by DAU 5884, and unaffected by AF-DX 116. Colonic ICC-IM receive excitatory inputs from cholinergic neurons via M receptor activation. Enhancing ICC-IM Ca release and Ano1 activation contributes to excitatory responses of colonic muscles.