Changes in shape and viability of cultured adult rabbit cardiac myocytes during ischemia/reperfusion injury.

The goal of this work was to define the distinction between irreversible structural changes and actual loss of cell viability during hypoxic/ischemic/reperfusion injury to one-day cultured adult rabbit cardiac myocytes. Myocytes were exposed to 5 mM NaCN and 20 mM 2-deoxyglucose (chemical hypoxia) or anoxia at pH 6.2 to simulate ischemia. Shortening and hypercontraction (cell rounding and blebbing) were monitored by bright field microscopy, and loss of viability was determined by nuclear labeling with propidium iodide. After both treatments, myocytes began to shorten after 30 minutes, and most were hypercontracted after 3 hours. 50% loss of viability did not occur until after 6 hours or more. To simulate reperfusion, myocytes were washed with fresh aerobic buffer at pH 7.4. Loss of viability was accelerated when cells were reperfused with Krebs-Ringer solution. This cell killing was prevented when myocytes were reperfused with nutrient culture medium instead of Krebs-Ringer solution. Both contracted and hypercontracted cells partially relaxed after reperfusion. These results indicate that structural changes (contraction, hypercontraction and blebbing) to adult cardiac myocytes are distinct from outright cell death caused by plasma membrane failure. Persistence of cell viability suggests that rescue of cardiac myocytes from necrotic cell death may be possible even very late in injury.