A novel intramuscular Interstitial Cell of Cajal is a candidate for generating pacemaker activity in the mouse internal anal sphincter

Karen I Hannigan,Sean M Ward,Salah A Baker,Holly J L Foulkes,Kathleen D Keef,Kenton M Sanders,Aaron P Bossey,Bernard T Drumm,Caroline A Cobine

doi:10.1038/s41598-020-67142-y

Karen I Hannigan, Sean M Ward + Show 7 more

Open Access

https://doi.org/10.1038/s41598-020-67142-y

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Journal: Scientific Reports	Publication Date: Jun 25, 2020
Citations: 8	License type: open-access

Affiliation: University of Nevada Reno

Abstract

The internal anal sphincter (IAS) generates phasic contractions and tone. Slow waves (SWs) produced by interstitial cells of Cajal (ICC) underlie phasic contractions in other gastrointestinal regions. SWs are also present in the IAS where only intramuscular ICC (ICC-IM) are found, however the evidence linking ICC-IM to SWs is limited. This study examined the possible relationship between ICC-IM and SWs by recording Ca2+ transients in mice expressing a genetically-encoded Ca2+-indicator in ICC (Kit-Cre-GCaMP6f). A role for L-type Ca2+ channels (CavL) and anoctamin 1 (ANO1) was tested since each is essential for SW and tone generation. Two distinct ICC-IM populations were identified. Type I cells (36% of total) displayed localised asynchronous Ca2+ transients not dependent on CavL or ANO1; properties typical of ICC-IM mediating neural responses in other gastrointestinal regions. A second novel sub-type, i.e., Type II cells (64% of total) generated rhythmic, global Ca2+ transients at the SW frequency that were synchronised with neighbouring Type II cells and were abolished following blockade of either CavL or ANO1. Thus, the spatiotemporal characteristics of Type II cells and their dependence upon CavL and ANO1 all suggest that these cells are viable candidates for the generation of SWs and tone in the IAS.

Highlights

The internal anal sphincter (IAS) is responsible for approximately 70% of resting anal pressure; an important property for maintaining faecal continence[1,2]
anoctamin 1 (ANO1) is highly expressed in Interstitial cells of Cajal (ICC) throughout the GI tract including the IAS14,29,31,32, but this conductance is not resolved in smooth muscle cells (SMCs) or the other type of interstitial cell found in GI muscles, platelet-derived growth factor receptor alpha-positive (PDGFRα+) cells
Since CavL and ANO1 antagonists block Slow waves (SWs) as well as tone in the IAS we have proposed that IAS-SWs are important for tone generation[7,8,13,14,26]

Summary

Introduction

The internal anal sphincter (IAS) is responsible for approximately 70% of resting anal pressure; an important property for maintaining faecal continence[1,2]. Pacemaker ICC in these regions are coupled electrically to one another and to adjacent smooth muscle cells (SMCs) via gap junctions allowing conduction of SWs from ICC to SMCs where excitation-contraction coupling occurs[15]. These cells are typically highly-branched stellate-shaped cells[16,17]. The cell-specific expression of ANO1 is important because antagonists of this conductance or genetic deactivation of Ano[1] can be used to examine the functional role of ICC in intact muscles. The effects of inhibition of CavL, hyperpolarisation of the Em and blockade of ANO1, were examined as these characteristics have previously been shown to alter the electrical activity, phasic contractions and tone in the IAS

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Conclusion