Effect of calcium ions on resting oxygen consumption of the myocardium

The effect of changes in extracellular calcium ion concentration (Cap2+) on myocardial resting O2 consumption (QO2R) was studied by direct ("cardiac arrest") and indirect (extrapolation) methods in the isolated rat heart perfused by the modified Langendorff technique. Cessation of heart beat by uncoupling excitation from contraction (Ca-free solution; 30 microM LaCl3- 2 mM NiCl2) decreased O2 consumption to 2.8-4.9 ml/100 g/min. Extrapolation of the total O2 consumption-left ventricular pressure development (LVPD) relationship (determined by stepwise elevation of perfusion pressure from 60 to 160 mmHg) to zero LVPD yielded a QO2R of 3.55 +/- 0.25 ml/100 g/min in the presence of 1.3 mM Cap2+. Elevation of Cap2+ from 0.65 to 3.9 mM increased QO2R significantly from 2.82 +/- 0.17 to 6.02 +/- 0.59 ml/100 g/min (p < 0.001). Elevation of Cap2+ from 1.3 to 2.6 mM increased O2 consumption from 2.4 +/- 0.6 to 4.1 +/- 0.5 ml/100 g/min, when heart beat was abolished by 2 mM Ni2+. The present findings indicate that QO2R is Cap2+ dependent in the rat heart.