Spontaneous Ca2+ transients in interstitial cells of Cajal located within the deep muscular plexus of the murine small intestine
Authors: Baker Salah A. , Drumm Bernard T. , Saur Dieter , Hennig Grant W. , Ward Sean M. , Sanders Kenton M. 
Published: January 2016

Key points

Interstitial cells of Cajal at the level of the deep muscular plexus (ICC‐DMP) in the small intestine generate spontaneous Ca2+ transients that consist of localized Ca2+ events and limited propagating Ca2+ waves.

Ca2+ transients in ICC‐DMP display variable characteristics: from discrete, highly localized Ca2+ transients to regionalized Ca2+ waves with variable rates of occurrence, amplitude, duration and spatial spread.

Ca2+ transients fired stochastically, with no cellular or multicellular rhythmic activity being observed. No correlation was found between the firing sites in adjacent cells.

Ca2+ transients in ICC‐DMP are suppressed by the ongoing release of inhibitory neurotransmitter(s).

Functional intracellular Ca2+ stores are essential for spontaneous Ca2+ transients, and the sarco/endoplasmic reticulum Ca2+‐ATPase (SERCA) pump is necessary for maintenance of spontaneity.

Ca2+ release mechanisms involve both ryanodine receptors (RyRs) and inositol triphosphate receptors (InsP3Rs). Release from these channels is interdependent.

ICC express transcripts of multiple RyRs and InsP3Rs, with Itpr1 and Ryr2 subtypes displaying the highest expression.

Interstitial cells of Cajal in the deep muscular plexus of the small intestine (ICC‐DMP) are closely associated with varicosities of enteric motor neurons and generate responses contributing to neural regulation of intestinal motility. Responses of ICC‐DMP are mediated by activation of Ca2+‐activated Cl− channels; thus, Ca2+ signalling is central to the behaviours of these cells. Confocal imaging was used to characterize the nature and mechanisms of Ca2+ transients in ICC‐DMP within intact jejunal muscles expressing a genetically encoded Ca2+ indicator (GCaMP3) selectively in ICC. ICC‐DMP displayed spontaneous Ca2+ transients that ranged from discrete, localized events to waves that propagated over variable distances. The occurrence of Ca2+ transients was highly variable, and it was determined that firing was stochastic in nature. Ca2+ transients were tabulated in multiple cells within fields of view, and no correlation was found between the events in adjacent cells. TTX (1 μm) significantly increased the occurrence of Ca2+ transients, suggesting that ICC‐DMP contributes to the tonic inhibition conveyed by ongoing activity of inhibitory motor neurons. Ca2+ transients were minimally affected after 12 min in Ca2+ free solution, indicating these events do not depend immediately upon Ca2+ influx. However, inhibitors of sarco/endoplasmic reticulum Ca2+‐ATPase (SERCA) pump and blockers of inositol triphosphate receptor (InsP3R) and ryanodine receptor (RyR) channels blocked ICC Ca2+ transients. These data suggest an interdependence between RyR and InsP3R in the generation of Ca2+ transients. Itpr1 and Ryr2 were the dominant transcripts expressed by ICC. These findings provide the first high‐resolution recording of the subcellular Ca2+ dynamics that control the behaviour of ICC‐DMP in situ.