Targeted gene transfer increases contractility and decreases oxygen cost of contractility in normal rat hearts

The aim of this study was to examine how global cardiac gene transfer of sarcoplasmic reticulum Ca²⁺-ATPase (SERCA2a) can influence left ventricular (LV) mechanical and energetic function, especially in terms of O₂ cost of LV contractility, in normal rats. Normal rats were randomized to receive an adenovirus carrying the SERCA2a (SERCA) or β-galactosidase (β-Gal) gene or saline by a catheter-based technique. LV mechanical and energetic function was measured in cross-circulated heart preparations 2-3 days after the infection. The end-systolic pressure-volume relation was shifted upward, end-systolic pressure at 0.1 ml of intraballoon water volume was higher, and equivalent maximal elastance, i.e., enhanced LV contractility, was higher in the SERCA group than in the normal, β-Gal, and saline groups. Moreover, the LV relaxation rate was faster in the SERCA group. There was no significant difference in myocardial O₂ consumption per beat-systolic pressure-volume area relation among the groups. Finally, O ₂ cost of LV contractility was decreased to subnormal levels in the SERCA group but remained unchanged in the β-Gal and saline groups. This lowered O₂ cost of LV contractility in SERCA hearts indicates energy saving in Ca²⁺ handling during excitation-contraction coupling. Thus overexpression of SERCA2a transformed the normal energy utilization to a more efficient state in Ca²⁺ handling and superinduced the supranormal contraction/relaxation due to enhanced Ca²⁺ handling.