Oxygen-induced enzyme release after irreversible myocardial injury. Effects of cyanide in perfused rat hearts

Abstract

The effects of 5 mM potassium cyanide (KCN) on creatine phosphokinase (CPK) release and cellular morphology were studied. Rat hearts were perfused with substrate-deficient media gassed with O2 or N2 (O2 medium, N2 medium) at 37 C, and effluent was collected for creatine phosphokinase analysis. Tissue fixation was with glutaraldehyde for light and electron microscopy. Experiments included the following: a) continuous perfusion with O2- or N2-medium in the presence of KCN; b) 45 or 60 minutes of perfusion with N2-medium followed by O2-medium for 15 or 180 minutes, respectively; c) 45 minutes of perfusion with N2-medium with KCN added 15 minutes before reoxygenation with O2-medium plus KCN; (4) 60 minutes of N2-medium plus KCN followed by O2-medium plus KCN for 180 minutes; d) as a control for irreversible injury, 21 minutes of perfusion with calcium-free O2-medium followed by 2.5 mM calcium-O2-medium ("calcium paradox"). The following results were seen: a) Initial CPK release occurred about 30 minutes later from hearts perfused with O2-medium plus KCN than from hearts perfused with N2-medium plus KCN. b) Upon reoxygenation after either 45 or 60 minutes of anoxia, hearts had a sudden peak of oxygen-induced CPK release. Most irreversibly injured cells were massively swollen and had sarcolemmal defects and contraction bands. Reversibly injured cells in the same hearts resembled normal myocardium. A previously unrecognized third population of cells is described. These cells were characterized by contraction bands but were not swollen, had intact sarcolemma, and contained both normal and damaged mitochondria with intramatrical calcium accumulation granules. It could not be determined if these cells were reversibly injured or in an early stage of irreversible injury. c) KCN added 15 minutes before reoxygenation of hearts after 45 minutes of anoxia inhibited the sudden peak of oxygen-induced CPK release but not a slow sustained release. Small to moderate numbers of cells in these hearts contained contraction bands. d) After 60 minutes, KCN completely inhibited both oxygen-induced CPK release and contraction band formation. e) Addition of calcium to calcium-free hearts caused both massive CPK release and contraction band formation. It is concluded that: the beginning of CPK release from oxygenated KCN-inhibited hearts requires about 30 minutes longer than from anoxic hearts; KCN can inhibit both oxygen-induced CPK release and contraction bands in irreversibly injured rat myocardial cells; sudden contracture of myocardial cells as occurs in the calcium paradox can result in massive CPK release; contraction bands occur in nonswollen cells, hence contraction bands can occur independently of massive cell swelling or membrane rupture. It is postulated that there may be two stages of irreversible myocardial injury; a) loss of control of contraction and b) progressive loss of mitochondrial and membrane integrity.