Anaerobic rat heart: Mitochondrial role in calcium uptake and contractility

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 fumarate‐dependent oxidation of NADH, (b) Ca⁺⁺ stimulated fumarate‐dependent 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.