Fig. 1

Application of electromechanical stimulation to rat myocardial slices. a Assessment of laser diffraction pattern. Peaks correspond to diffraction bands—the bright, central band corresponds to a zero-order band (grey), while the smaller bands on the left and right correspond to the less intense first-order bands (red). The distance between the zero-order and first-order band can be measured and used to calculate sarcomere length. b Percentage stretch required to set the average diastolic rat myocardial slice sarcomere length. Rat myocardial slices were progressively stretched until a diffraction pattern equivalent to SL = 2.0 μm was achieved. The % stretch was then measured using calipers. This was repeated at 0.1-μm intervals until SL = 2.4 μm. A linear regression was used to estimate SL (r² = 0.4776, y = 41.67 × −69.26) (SL = 2.0 N = 11, SL = 2.1 N = 16, SL = 2.2 N = 14, SL = 2.3 N = 15 and SL = 2.4 N = 12). c Top—rat myocardial slice visualised using a macroscope. The slice is placed on a mm grid and the green rectangle highlights the aligned portion of the myocardial slice. Bottom—custom-made 3D-printed plastic rectangular rings are attached to opposite ends of the aligned portion of the myocardial slice using surgical glue. Rings are attached perpendicular to myofibril orientation. d Myocardial slice attached to the posts of a custom-made stretcher using rings. Images show the different stretches required to achieve SL = 1.8–2.4 μm in rat myocardial slices. e Custom-made culture chamber. Myocardial slices are superfused with culture media. Media was oxygenated directly in the culture chamber. Field stimulation was provided via carbon electrodes. f Six-well plate with Transwell inserts. Unloaded myocardial slices placed on a porous membrane and each well filled with 1 mL of culture media. N = number of myocardial slices. Mean ± standard error is shown on graphs. Source data are provided as a Source Data file