Effect of low temperatures on high energy phosphate compounds in isolated hearts from a hibernator and a nonhibernator

Abstract

1. 1. Isolated perfused hearts from the ground squirrel ( Citellus tridecemlineatus) remained functional at 35, 20, 12 and 6°C, whereas albino rat hearts ceased beating at an average temperature of 15.7°C. 2. 2. ATP was not depleted in rat hearts at the lower temperatures, but the phosphate potential, ( ATP × 10 3/ADP × Pi ), was decreased by 38%. 3. 3. By contrast, CP and ATP were decreased significantly in ground squirrel hearts at 12 and 6°C, but the phosphate potential was maintained at control levels (35°C). 4. 4. During hypothermia, the energy state of cardiac tissue from the hibernator is apparently balanced between the synthesis, translocation, and utilization of high energy phosphate compounds. 5. 5. Decreased levels of these compounds are sufficient to accommodate the reduced needs of the tissue at low temperatures.