Total ischemia in dog hearts, in vitro 2. High energy phosphate depletion and associated defects in energy metabolism, cell volume regulation, and sarcolemmal integrity.

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Abstract
The capacity of tissue, injured by varying periods of total ischemia, to perform integrated cellular functions, was assessed to learn the nature of the associations between the decreasing ATP of the ischemic tissue and the appearance of defective high energy phosphate regeneration, cell volume and ion regulation and membrane permeability. Total ischemia in vitro was produced by incubating papillary muscles from dog hearts at 37.degree. C. Slices were cut from control tissue and from injured tissue after 60-150 min of total ischemia. These slices were incubated in oxygenated phosphate Krebs-Ringer phosphate buffer containing 14C-inulin to assess their capacity to resynthesize ATP and CP [creatine phosphate], to maintain ion gradients and water content, and to retain membrane impermeability to inulin and creatine. Apparently there was a close association between ATP depletion and the failure of the damaged tissue to regenerate high energy phosphates and to preserve cell volume and ionic regulation. As long as the ATP of the tissue was not depleted below 5 .mu.mol/g dry wt prior to incubation, no cellular abnormalities were detected by subsequent aerobic incubation of slices of the injured tissue. Lower ATP levels were associated with depressed high energy phosphate resynthesis and failure of cell volume regulation. These defects preceded the development of overt membrane damage, which occurred only after the tissue ATP content decreased to < 2.0 .mu.mol/g. When overt membrane damage was present, it was associated with marked impairment of other integrated cellular functions. Although the pathogenesis of the membrane damage in ischemia is unknown, its presence is an objective sign of lethal injury in this system.