Increase in Content of Glycogen Phosphorylase during Ischemia in Isolated Rabbit Heart

The amount of a 97-kDa protein in the sarcoplasmic reticulum-enriched microsomal fraction from rabbit heart changed in a manner dependent on the oxygenated condition after global hypothermic ischemia and subsequent normothermic reperfusion. Isolated hearts were immersed in physiologic saline for 0h (control group) or 1, 2 and 3h at 4°C (ischemia group) and were subjected to 40-min reperfusion at 37°C after 1h of hypothermic ischemia (reperfused group). The amount of the 97-kDa protein in the microsomal fraction apparently increased after ischemia, but decreased after reperfusion. The N-terminal amino acid of the protein was blocked and two internal sequences were determined, demonstrating the 97-kDa protein to be glycogen phosphorylase. A polyclonal antibody against rabbit skeletal muscular glycogen phosphor-ylase (GP) stained only the 97-kDa protein in the microsomal fraction in Western blot analysis. Microsomal fractions isolated from rabbit brain, liver, spleen, and white skeletal muscle were also examined by Western blot analysis using anti-GP. Liver and skeletal muscle contained a 97-kDa protein that reacted with anti-GP in control preparations. Ischemia induced a modest increase in the amount of the 97-kDa protein skeletal muscle microsomes, whereas no change in the amount of the protein occurred in liver microsomes. The results indicate that alteration in the energy metabolism from ischemia to the subsequent reperfusion is associated with the amount of GP.