[Dynamics and pathogenesis of ischemic contracture of the heart]

In experiments on 34 dogs, the authors studied myocardial rigidity, ATP levels and Ca2+-accumulating function of the membranes of the sarcoplasmic reticulum (SR) in the external (subepicardial) and internal (subendocardial) layers of the myocardium at 1 and 2 h of total ischemia at 37 degrees C and also 30 min after cardiac reperfusion by heterotopic transplantation. It was revealed that contracture changes in ischemia first affect the internal and then the external layer of the myocardium which corresponds to the initial and completed phases of ischemic contracture (IC) of the heart, correspondingly. IC of the heart is irreversible and in cases of total contracture of all layers of the myocardium (the completed phase) the heart loses contractile function. Changes in the contractility in the external and internal layers of the myocardium show a stronger inverse correlation with the capacity of SR membranes to absorb Ca2+ rather than with ATP levels in the tissues which indicates an essential role of the Ca2+ accumulating function of SR in the pathogenesis of IC.