Evidence For The Possible Association Between Calcium Transient Of Isolated Ventricular Cardiomyocytes And Exercise Capacity In Rats

The association between the whole cell intracellular Ca 2+ transients ([Ca 2+ ] i ) of isolated cardiomyocytes and intrinsic exercise capacity in rats was evaluated. Standard performance (SP; n= 120) and high performance (HP; n= 36) rats were previous selected in a treadmill progressive exercise test accordingly to total exercise time until fatigue (TTF). The SP group encloses rats with TTF between 16.63 and 46.57 min and the HP encloses rats with TTF higher than 46.57 min. Oxygen consumption at the point of fatigue (VO 2max ) was measured by an open‐flow indirect calorimeter. The [Ca 2+ ] i transients were measured by confocal microscopy in cardiomyocytes loaded with fluo‐4 AM. Statistical significance was assessed by t test, Mann‐Whitney test and linear regression (means ± SE). The study was approved by the Ethical Committee at the Federal University of Minas Gerais. The HP rats presented high VO 2max (56.72 ± 0.54 mL.Kg −1 .min −1 , n= 6) when compared to SP rats (40.01 ± 0.42 mL.Kg −1 .min −1 , n= 6; P≤0.05). The [Ca 2+ ] i transient peak was 4.18 ± 0.12 and 5.79 ± 0.34 for SP (n= 5 rats and 83 cells) and HP (n = 4 rats and 61 cells) groups, respectively (P≤0.05). The [Ca 2+ ] i transient peak was positively correlated with the maximal treadmill speed in the progressive test (r = 0.81; P≤0.05). The data indicated that the high intrinsic exercise capacity is closely related to higher [Ca 2+ ] i transients in isolated ventricular cardiomyocytes.