Increased myocyte fragility following anoxic injury

Abstract

The ability of cells in anoxic-perfused hearts to withstand two types of physical stresses (stretching and swelling), in the absence of reoxygenation was determined. Isolated rat hearts were perfused for 20, 40, or 60 mins with anoxic buffer after which hearts were either reoxygenated for 20 mins or exposed for 15 s to a physical stress caused by inflation of a intraventricular balloon to an appropriate volume (0.35 ml), while maintaining anoxic perfusion for an additional 20 mins. At 20, 40, or 60 mins of anoxic perfusion, reoxygenation induced CK releases of (n = 5) 14.13 +/- 13.15, 62.42 +/- 2.87, and 83.22 +/- 6.41 IUCK/g wet wt, respectively. After 0.35 ml balloon inflation, in the absence of reoxygenation, corresponding CK releases were respectively 8.10 +/- 1.63, 39.13 +/- 8.27, and 59.64 +/- 2.57 IUCK/g wet wt. Increasing the volume of balloon inflation from 0.2 to 0.6 ml at a constant (60 mins) duration of anoxic perfusion resulted in a corresponding increase in CK release. Control hearts released no CK even following 0.6 ml balloon inflation. In the second experimental protocol, hearts were perfused for 30, 45, 60, or 75 mins with isotonic (300 mOsm) anoxic buffer followed by 15 mins with hypotonic (150, 200, or 250 mOsm) anoxic buffer. At each time interval there was a graded increase in cell injury as the duration of anoxia was increased. Control hearts perfused for 75 mins with oxygenated buffer released no CK when perfused with 150 mOsm buffer. Electron microscopy revealed that injured cells contained lesions in sarcomere attachment sites (balloon) and/or in sarcomere-sarcolemmal membrane connections (osmotic). These results suggest that hearts develop latent injury during prolonged anoxic perfusion which can be exposed by application of a physical stress. The extent of injury increases with both the duration of anoxic perfusion and with the degree of stress. It is hypothesized that following prolonged anoxic perfusion, myocardial cells become fragile and respond abnormally to a variety of stresses including the ventricular distensions hypotonic cell swelling, or the effects of reoxygenation.