Low extracellular Ca2+ and enzyme release in the perfused rabbit heart

Abstract

Previous studies have shown that the well-oxygenated perfused rabbit heart releases creatine kinase when treated with the calcium antagonist drug verapamil (VER) in a dose-related manner. It is possible that this effect is related to Ca²⁺ ion deprivation of the sarcolemma. This possibility was explored by perfusing hearts with low Ca²⁺ (0.5, 0.23, 0.15, and 0 mM) versus a control group (1.27 mM Ca²⁺) for 60 min. Low Ca²⁺ perfusion was associated with (i) reduction in the heart rate – left ventricular systolic pressure product and O₂ consumption, (ii) tendency for the coronary sinus flow to increase, (iii) electromechanical dissociation, prolongation of atrioventricular conduction and QT interval, and (iv) decrease in myocardial glycogen. Lower total adenosine nucleotides were found only in the 0 mM Ca²⁺ group. As the Ca²⁺ concentration was reduced, the hearts lost increasing amounts of creatine kinase, aspartate aminotransferase, and lactate dehydrogenase. These results confirm the importance of Ca²⁺ ions in contractile and electrical cardiac functions and show that decreased availability of this cation leads to increasing enzyme leakage resembling that seen in VER-treated hearts.