Simultaneous high-resolution electrophysiology measurements and motion tracking of ex vivo rat uterine smooth muscle activity

Uterine smooth muscle undergoes electrical, chemical and mechanical transients during phasic contraction. The spread of electrical activity precedes the mechanical contraction of muscle fibers, and the initiation and coordination of these events is critical to uterine function, in both pregnancy and non-pregnancy. Characterization of non-pregnant activity is scarce, and understanding of the relationship between electrical and mechanical events is not well understood. Isolated uterine horns from virgin female Wistar rats were used in this study. Electrical and mechanical activity were assessed ex vivo using high-resolution surface electrodes and motion tracking. Electrophysiology data were analyzed to provide frequency and timing metrics; displacement and velocity were quantified from the motion tracking data. Major coordinated electrical events were correlated with longitudinal displacement of tissue markers, with the peak displacement occurring at or near the point of electrical signal initiation. 82% of electrical slow wave events were associated with mechanical displacement of tracking points. Minor uncoordinated electrical events were accompanied by little or no displacement, indicated a level or coordination is required to achieve tissue-level contraction. Electrical slow wave propagation occurred at a higher speed (0.60 ± 0.04 mm/s) than mechanical tissue displacement velocity (0.42 ± 0.39 mm/s, p = 0.0024), and electrical propagation speed was lowest during metestrus, when compared with estrus (p = 0.0042) and diestrus (p = 0.0066). This technique advances our understanding of the electro-mechanical properties of the non-pregnant rat uterus and provides an avenue to measure electrical-mechanical coupling in ex vivo uterine tissue preparations.