Abstract
In order to evaluate the manner by which fumarate enhances contractility in the anaerobic heart, we examined Ca^++^ movements in isolated heart mitochondria and in the isolated perfused heart. Our experiments showed that in isolated antimycin A plus cyanide treated mitochondria: (a) Ca^++^ uptake was promoted by electron transport generated by fumarateβdependent oxidation of NADH, (b) Ca^++^ stimulated fumarateβdependent oxidation of NADH, (c) the ratio of Ca^++^ uptake:NADH oxidized was 1.7 and (d) the Ca^++^ sequestered is transiently highly mobile and is rapidly released upon collapse of the membrane potential. In anaerobic hearts perfused with glucose plus fumarate, malate and glutamate Ca^++^ levels were the same as those in oxygenated hearts while in anaerobic organs perfused with or without glucose Ca^++^ content was appreciably lower. Succinate production in anaerobic heart perfusions was related to: (a) an increased retention of Ca^++^ by the heart, (b) a diminution in peak aortic pressure generated by cardiac contractions and (c) an increase in heart rate. The information obtained indicates that mitochondria have a capability for Ca^++^ movement which might be used physiologically, particularly in fumarate perfused anaerobic hearts, to assist the mechanism for contraction and relaxation of the heart.