Changes in interstitial cells of Cajal calcium activity in a diabetic mouse model of delayed gastric emptying

Interstitial cells of Cajal (ICC) regulate gastrointestinal motility by generating electrical slow waves that orchestrate downstream calcium (Ca^{2 +}) waves and coordinate smooth muscle contractions. A reduced ICC number has been reported in diabetic gastroparesis patients and in mouse models of delayed gastric emptying (DGE). However, functional changes in ICC propagating across the gastric regions in intact stomach are not well understood. The aim of this study was to develop an imaging approach to visualize ICC Ca²⁺ waves in mouse stomach and determine spatiotemporal changes in mice with DGE. Tamoxifen-treated B6.GCaMP5-KitCreERT2 female mice were used as non-diabetic controls (Non-Db), while mice treated with streptozocin to induce diabetes were categorized as having normal (Db-NGE) or delayed (Db-DGE) gastric emptying based on emptying of solids. The ICC Ca²⁺ network was imaged from excised intact mouse stomachs and subsequently opened along the lesser curvature and pinned flat. ICC Ca²⁺ waves typically propagated along the greater curvature from the fundus-corpus line toward the antrum. The propagation length of ICC Ca²⁺ activity was significantly decreased in Db-DGE compared to Non-Db and Db-NGE and correlated to longer GE times. There was also a decrease in frequency, and the velocity was significantly faster in stomachs from Db-DGE compared to Non-Db and Db-NGE. All experimental groups exhibited similar proportions of aberrant Ca²⁺ propagation patterns (e.g., retrograde waves), but ectopic initiation only occurred in Db-DGE stomachs. Thus, DGE is possibly driven by dysfunction in Ca²⁺ activity in the ICC network that propagates rapidly over short distances, resulting in uncoordinated, non-phasic muscle activity. KEY POINTS: Dysfunction of the interstitial cells of Cajal (ICC) has been implicated in diabetic gastroparesis but the changes in spatiotemporal properties of ICC network activity are not known. We developed an ex vivo Ca²⁺ imaging approach to visualize ICC network activity across the entire stomach and determined changes in ICC Ca²⁺ activity in a diabetic mouse model of delayed gastric emptying (GE). Decreased frequency and increased velocity of ICC Ca²⁺ activity was observed in stomachs of diabetic mice with delayed GE. Ectopic initiation was a key feature associated with delayed GE. The propagation length of ICC Ca²⁺ activity was inversely correlated to GE times and significantly reduced in stomach preparations from diabetic mice with delayed GE.