X-ray diffraction studies of whole rat heart during anoxic perfusion.

Equatorial x-ray reflections were recorded from the ventricular region of whole rat heart, during the transition from normoxia to anoxia. The intensity ratio of the 1.0 and 1.1 equatorial reflections (I 1.0/I 1.1) was 2.96 during normoxic perfusion, decreasing to 0.37 after 115 minutes of anoxic perfusion and closely parallel those reported between partially dissected relaxed and rigor vertebrate heart muscle (1.2). The peak positions of these reflections both increased by ca. 5% during anoxic perfusion indicative of a lateral expansion in the sarcomere filament lattice. These results indicate that the process of anoxia leads to the condition of rigor in which the majority of the myosin cross-bridges bind to the thin filament. Using this technique global changes in whole heart structure can be studied, and due to the ease of perfusion of the heart, biochemical and physiological problems may be investigated in relation to the structure of the heart as a whole. This may be of clinical interest, particularly in terms of investigations into organ preservation and transplantation. This is believed to be the first occasion where intact muscular organs have been studied in this way.