A specialized population of intramuscular interstitial cells of Cajal regulates motility within the mouse oesophagogastric junction.

The oesophagogastric junction (EGJ) is a high-pressure zone consisting of the lower oesophageal sphincter (LES), distal oesophagus and crural diaphragm. Phasic electrical activity associated with phasic contractions has been demonstrated in the human distal oesophagus as well as in the dog proximal LES but is absent from the dog distal LES where phasic contractions are also absent. As electrical slow waves are dependent on activation of anoctamin 1 (ANO1) channels in interstitial cells of Cajal (ICC), we hypothesized that differences in contractile activity between regions may be correlated to differences in ICC Ca signalling behaviours. Using ICC-specific GCaMP6f mice we found that unlike the LES where only asynchronous Ca transients were observed, two distinct ICC Ca signalling behaviours were present within the distal oesophagus. Type I intramuscular interstitial cells of Cajal (ICC-IM) exhibited localized asynchronous Ca transients that were insensitive to ANO1 or voltage-dependent Ca channel (VDCC) inhibition but abolished by inhibiting endoplasmic reticulum (ER) Ca release. In contrast type II ICC-IM exhibited rhythmic, whole-cell Ca transients that were inhibited by ANO1 or VDCC antagonists revealing the underlying asynchronous Ca release events. Phasic contractile activity in the mouse distal oesophagus was also inhibited by ANO1 and VDCC antagonists, suggesting a link between type II ICC-IM Ca signalling and contraction. mRNA encoding IPR1 and ANO1 channels was expressed in ICC-IM. These data suggest that type II ICC-IM are responsible for generating rhythmic, phasic activity in the distal oesophagus and that Ca release occurs in ICC-IM via IP receptors (IPRs), which in turn activates ANO1, causing depolarization, Ca influx via VDCCs and contraction. KEY POINTS: The oesophagogastric junction (EGJ) is a high-pressure zone that prevents acid reflux into the oesophagus. Disrupted EGJ motility is associated with gastro-oesophageal reflux disease or achalasia. The lower oesophageal sphincter (LES) generates tone, whereas the adjacent distal oesophagus exhibits phasic contractions. Both activities are dependent on anoctamin 1 (ANO1) and voltage-dependent Ca channels (VDCCs). Only intramuscular interstitial cells of Cajal (ICC-IM) are present in the EGJ, yet two distinct ICC Ca signalling behaviours were apparent. Type I ICC-IM exhibited localized asynchronous Ca transients, whereas type II ICC-IM exhibited rhythmic whole-cell Ca transients that were inhibited by ANO1 and VDCC antagonists revealing the underlying asynchronous Ca transients that were abolished by IP receptor (IPR) inhibition. mRNA encoding IPR1 and ANO1 was expressed in all ICC, suggesting that Ca release via IPRs leads to ANO1 activation, depolarization and subsequent Ca influx via VDCCs. Type II ICC-IM likely participate in generating pacemaker activity and regulating EGJ function.