Measuring Cardiomyocyte Contractility and Calcium

Cardiomyocyte cell shortening (CS) and intracellular Ca²⁺ transients (CaT) were measured using Fura-2 AM as described previously [6 (link), 24 (link), 25 (link)]. Briefly, cells were stimulated electrically by a field stimulator (IonOptix, MA) at a frequency of 0.5 Hz. CaT and CS amplitudes reached the steady state within 30 sec after start of pacing stimulation. Therefore, we recorded CaT and CS from 30 sec to 40 sec after start of pacing at the rate of 0.5 Hz. We defined the values of CaT peak and CS peak, which were calculated from averaging 10 consecutive steady CaT waveforms and 10 CS waveforms by using IonOptix analysis software, as the peak CaT and the peak CS of each cardiomyocyte. Ca²⁺-induced fluorescence at 505 nm was measured by excitation at 340 and 380 nm using a dual-excitation spectrofluorometer. The intracellular calcium concentration was calculated as the ratio of the fluorescence emission intensities at these 2 excitation wavelengths [6 (link), 24 (link), 25 (link)].
To determine the dose-dependent effect of landiolol on CS in isolated normal and failing cardiomyocytes, we measured CS with various doses of landiolol (from 0 nM to 1000 nM).