Background:

In prior studies in pigs, ivabradine reduced infarct size even when given only at reperfusion and in the absence of heart rate reduction (atrial pacing).

Methods:

Ventricular cardiomyocytes were isolated enzymatically from C57Bl/6J mouse hearts (n=15), aliquoted and incubated in Tyrode buffer ± ivabradine (3 µM) for 30 min, respectively. Simulated ischemia ± ivabradine was induced (hypoxia, pH 6.5, 310 mOsm/l, 60 min) and followed by reperfusion ± ivabradine (normoxia, pH 7.4, 250 mOsm/l, 5 min). Viability (trypan blue exclusion) was quantified in > 200 cells/per preparation. In a subset of hearts (n=5), cardiomyocytes were loaded with CM-H₂DCFDA (5 µM) as an indicator for reactive oxygen species (ROS) formation. Intracellular fluorescence was detected before and after simulated ischemia ± ivabradine.

Results:

Viability was comparable at baseline (control, 73±4%; ivabradine, 73±2%), and it remained relatively stable with 60 min normoxia (53±2%). Simulated I/R reduced cardiomyocyte viability (9±3%), whereas it was better preserved with ivabradine (27±2%, p=0.026 versus I/R). Preliminary data indicate a reduction of ischemia-induced ROS formation (3.1±0.4 a.u.) by ivabradine (2.0±0.4 a.u.).

Conclusion:

Ivabradine improves ventricular cardiomyocyte viability during simulated I/R, possibly by reduction of ROS formation.