Preservation of metabolic reserves and function after storage of myocytes in hypothermic UW solution

Isolated rat myocytes coldstored anaerobically up to 24 h in University of Wisconsinsolution lost 95% of their ATP and 100% of their glycogen. Theyunderwent contracture when rewarmed in a Krebs-Henseleit (KH) mediumthat contained Ca unless Ca addition was delayed. In the latter case,cell function, measured by stimulation-induced cell shortening, wassurprisingly well retained. Aerobically stored cells were resistant toCa on rewarming, although 96% of glycogen was still lost, along with46% of ATP. Cells that were incubated for 48 h aerobically withthe substrates glucose and pyruvate at pH 6.2 retained 77% of theirATP and 59% of their glycogen, with good cell morphology. At pH 6.2, the demand for ATP was only 55% of that at pH 7.4. However, afterrewarming, these cells functioned no better than anaerobically storedcells, although their inotropic response to isoproterenol was improved.We conclude that 1) aerobic conditions with substrates atlow pH preserve myocyte metabolic reserves well for 48 h, partlyby reducing the demand for ATP; 2) rewarming conditions arecritical for anaerobically stored cells with metabolic stores that areseverely depleted; and 3) unloaded cell function issurprisingly insensitive to a period of severe metabolic deprivation.