REGIONAL CHANGES IN CALCIUM WAVES GENERATED BY INTERSTITIAL CELLS OF CAJAL IN A MOUSE MODEL OF DIABETIC GASTROPARESIS

Background: Interstitial cells of Cajal (ICC), electrically active cells found throughout the gastrointestinal tract, generate spontaneous electrical slow waves, and transmit these waves to smooth muscle cells in the gut to produce phasic contractions. A reduction in the number of ICC has been reported in both humans and mice with diabetic gastroparesis. The aim of this study was to investigate regional changes in ICC Ca²⁺ waves by imaging the full thickness gastric body and antrum. Methods: Tamoxifen treated (6weeks) B6 GCaMP5(-td) KitCreERT2 female mice were treated with streptozocin (STZ) to induce diabetes (10weeks) or remained untreated and categorized as non-diabetic control (C), diabetic (D) with normal gastric emptying, or diabetic with delayed gastric emptying (DG) based on gastric emptying of solids (slower than 97.5^th percentile of normal range). Calcium signals from ICC were imaged in (1) unopened, intact stomachs and (2) stomach preparations opened along lesser curvature and pinned flat. Analyses were performed using a pipeline developed in MATLAB. Forty regions of interest (ROI) covered the entire path of propagating Ca²⁺ waves, were independently analyzed resulting in output measures of amplitude, frequency, interval, velocity, and length of propagation. Results: The velocity of ICC Ca²⁺ waves was significantly slower in DG compared to D in the unopened, intact stomach (0.4±0.1 mm/s, 0.5±0.16 mm/s, respectively; p=0.0002; N=40 ROI) and the interval was longer in DG compared to D (12±0.85 (s), 10±1.6 (s), respectively; p<0.0001; N=40 ROI). In the unopened intact stomach, propagation of slow wave in DG covered only 57.5% of the signal points compared to 75% and 72.5% in D and C respectively. In the open stomach at the greater curvature of the antrum, the velocity was also significantly slower in DG compared to D (0.28±0.006 mm/s, 0.3±0.004 mm/s respectively; p < 0.0001; N=40 ROI). The interval (s) was also longer in DG compared to D (10±0.16 (s), 8±0.02 (s), respectively; p<0.0001; N=40 ROI).In the open stomach at the greater curvature of the body, the velocity was faster in DG compared to D (0.4±0.005, 0.3±0.006 mm/s, respectively; p < 0.0001; N=40 ROI) (Figure 1). No significant difference in the interval was detected in the open greater curvature of the body. No wave fronts were observed in the fundus or lesser curvature at any region in any preparation from any group. Similarly, in the intact stomach. Conclusion: For the first time, we were able to investigate regional changes in full thickness intact stomach in B6 kit-CRE ERT2 GCaMP5 mice with diabetic gastroparesis. Further studies on the mechanisms underlying these regional functional variations using a larger sample are required. Funded by NIH R01 DK127992