The Effect of Exercise Training on Ca2+ Wave Probability After Myocardial Infarction Depends on Cardiac Function at Onset of Training.

Background Altered Ca 2+ handling in cardiomyocytes contributes to contractile dysfunction and increased risk of arrhythmias in heart failure. Exercise training (ET) can improve Ca 2+ handling, with potential positive effects on contractile performance and risk of arrhythmias. We hypothesized that the effect of ET on pathological Ca 2+ handling associated with arrhythmias, depends on the cardiac function at onset of ET. Method and Results Myocardial infarction was induced in male Wistar rats by ligation of the left coronary artery. One week after induction of infarction, rats were stratified by echocardiographic parameters to a non-failing group (MI+) and a failing group (CHF). Rats from both groups were randomized into a five-week high-intensity exercise training group (ET) or a sedentary control group (SED). Each training session consisted of five 8 minutes intervals at 80-90% of the running speed at maximal oxygen uptake (VO 2max , ml/kg/min), interspersed with two-minute periods at 60% running speed. After ET, ET-CHF had 24% higher VO 2max compared to SED-CHF (57±3 vs. 44±2, p 2max compared to SED-MI+ (64±5 vs. 47±2, p Ca 2+ wave probability and parameters of Ca 2+ handling were analyzed by Two-Way ANOVA to give overall values at 1, 2 and 4 Hz stimulation during ISO exposure. Overall Ca 2+ wave frequency in isolated cardiomyocytes during a 10 seconds pause following field stimulation was reduced by 31% in ET-CHF compared to SED-CHF (69+6 vs. 100+6%, p 2+ reuptake rate in ET-CHF decreased by 16% compared to SED-CHF (84±3 vs. 100±3%, p 2+ transient amplitude was 17% lower in the ET-CHF compared to SED-CHF (p 2+ content. Interestingly, the opposite effect on Ca 2+ wave frequency was observed in ET-MI+ rats: Overall Ca 2+ wave frequency was 35% higher in ET-MI+ compared to SED-MI+ (135+9 vs. 100+8%, p 2+ reuptake rate in ET-MI+ was 7% lower than SED-MI+ (p 2+ content or Ca 2+ transient amplitude. Conclusion ET had opposite effects on Ca 2+ wave probability in CHF and MI+ rats. These findings indicate that the effect of ET on Ca 2+ handling after myocardial infarction could depend on the cardiac function at onset of ET.