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INTRODUCTION: Rhythmic ‘slow waves’ and ‘spikes’ are key bioelectrical mechanisms underpinning gastrointestinal motility, but their function in health and disease is poorly defined. The gastroduodenal junction (GDJ) demarcates the stomach and duodenum functionally and electrically. In this study we aimed to elucidate the nature of electromechanical coupling across the in vivo (GDJ) using high-resolution electrical mapping and simultaneous contractile measurements. From prior studies, we hypothesized: 1) slow waves cannot propagate into the GDJ, 2) spikes may propagate across the GDJ, and 3) contractile amplitude is related to spike patch duration. METHODS: A 3D-printed cradle, anatomically-specific to the GDJ, was designed to house custom flexible-printed-circuit electrode arrays (256 electrodes, 5 mm apart). Following ethical approval, crossbred-weaner pigs ( N=3) were anesthetized with propofol, and the stomach exposed via midline laparotomy. An EndoFLIP catheter (16 electrodes, 10 mm apart; Medtronic, MN, USA) was inserted orally and positioned across the GDJ to estimate luminal diameter. The electrode cradle was positioned on the serosa to measure GDJ bioelectrical activity. Frequency, propagation, duration, and amplitude were quantified and compared using the Student’s t-test. Spatiotemporally associated slow waves, spikes, and contractions were assessed using a Pearson’s correlation test. RESULTS: Electrical mapping techniques were able to capture slow wave ( N=90) and spike ( N=183) activity in spatiotemporal detail. The stomach and duodenum had significant differences in slow wave frequency (4.5 ± 0.4 vs. 18.2 ± 0.7) cpm (p<0.005). Supporting hypothesis 1, no slow waves were measured in the pylorus. Spikes measured in the pylorus could be isolated to this region (19.3%), also measured in the duodenum (48.2%) or antrum (20.5%), or propagate to both organs (12.0%), supporting hypothesis 2. Slow waves occurred (0.01 ± 0.23) s before associated spikes and overlapped (77.1 ± 33.7) mm2. Spikes occurred (0.80 ± 0.61) s before associated contractions and contractile amplitude was related to spike patch duration (r=0.54, p=0.01), supporting hypothesis 3. 22.4% of all spikes were associated with a reduction in luminal diameter, supporting hypothesis 3 and implying most spikes were coupled to longitudinal or isometric contractions. CONCLUSIONS: This study establishes a research pipeline and foundational data for in vivo measurement of electrophysiological and contractile events in the GDJ. Preliminary results indicate that bioelectrical events may be useful biomarkers for characterizing the mechanisms underpinning electromechanical coupling of the GDJ. Funding was sourced from a Marsden Fast-Start grant from the Royal Society Te Aparangi, New Zealand. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.