Contracture of isolated rat heart cells on anaerobic to aerobic transition

Adult rat heart myocytes prepared by collagenase perfusion show a progressive loss of adenylate energy charge and total adenine nucleotide as a function of time of anaerobic incubation in the absence of glucose. Re-aeration of the rod-shaped anaerobic cells produces a population of viable rounded cells in hypercontracture. The round cells show extensive morphological dislocations but remain metabolically competent in that they 1) restore adenosine 5'-triphosphate levels to the extent permitted by the depleted adenine nucleotide pool: 2) reestablish a low Na+-K+ ratio; and 3) restore creatine phosphate to 73% of control. The hypercontracture on re-aeration of anaerobic myocytes closely resembles an analogous contracture of heart cells in situ produced when hypoxic perfused hearts are reoxygenated, the so-called "oxygen paradox." Both processes are eliminated by inclusion of glucose during the anaerobic phase and by inhibitors of respiration and uncouplers of oxidative phosphorylation added before reoxygenation. Mitochondria in the hypercontracted myocytes retain high acceptor control ratios. Contracture on re-aeration occurs to nearly the same extent in the presence of either mM Ca2+ or 0.1 mM EGTA. Contracture appears related to dislocations in intracellular Ca metabolism that result from the declining energy charge and depleted nucleotide pool produced during anoxic incubation.