Panel A depicts an intact cardiomyocyte secured between glass rods linked to a piezoelectric length controller and a force transducer. Panel B is a line graph showing the length profile over time, with annotations for stretch-release cycles and the onset of XB inhibitor perfusion. The x-axis is labeled Time [seconds] and the y-axis is labeled Length profile. Panel C is a line graph showing sarcomere length tracing over time, with the x-axis labeled Time [seconds] and the y-axis labeled Sarcomere length [micrometers]. Panel D is a line graph showing force tracing over time, with the x-axis labeled Time [seconds] and the y-axis labeled Force [micronewtons]. Panels E and F are zoomed-in line graphs of force tracings before and after XB inhibition, respectively, with the x-axis labeled Time [seconds] and the y-axis labeled Force [micronewtons]. The graphs illustrate the changes in sarcomere length and force before and after the administration of a crossbridge inhibitor, highlighting the progressive increase in baseline sarcomere length and decrease in baseline force following XB inhibition.
Experimental approach to measure diastolic XBs in intact cardiomyocytes. All intact cell experiments were performed at 37°C, and cells were stimulated at 4 Hz. (A) An intact cardiomyocyte was attached to the glass rods that connected to the piezo length controller and the force transducer. (B) A trapezoid stretch-release protocol was applied during a prolonged diastolic interval (pacing paused) to obtain the force–SL relation. The cell was then perfused with 20 mM BDM, a XB inhibitor. The stretch-release was repeated after contraction had completely stopped. (C and D) Representative tracings of SL (C) and force (D) show that, following XB inhibition, the cell gradually ceased beating, accompanied by a progressive increase in baseline SL and a decrease in baseline force. (E and F) Show zoomed-in force tracings before and after XB inhibition. The difference in up-ramp force (highlighted in blue) measured before and after XB inhibition was used to calculate the extent of diastolic XBs.