After prolonged exposure to low temperatures (1 degree and 4 degrees C), human atrial trabeculae show poor recovery of contraction. At somewhat higher temperatures (12 degrees and 20 degrees C), recovery is much better (Keon and associates. Ann Thorac Surg 1988;46:337-41). Although better preservation of
adenosine triphosphate and therefore improved contractile recovery might be expected after exposure to lower temperatures, it remained possible that, below a certain temperature,
adenosine triphosphate-generating mechanisms could be slowed more than
adenosine triphosphate utilization. To investigate this phenomenon further, we followed the time course of metabolic changes in human atrial appendages, harvested during cardiac bypass operations, at 1 degree, 4 degrees, 12 degrees, and 20 degrees C using high-resolution 31P and 1H nuclear magnetic resonance spectroscopy. The results are quantitated by correlation with data obtained from biochemical assays on quick-frozen tissues. Initial
adenosine triphosphate levels in myocytes of human atrial appendages are 3.3 to 4.3 mumol.gm-1 tissue wet weight. At 20 degrees C,
adenosine triphosphate disappears after 6 hours; at 12 degrees C, about half the initial
adenosine triphosphate is still observable at this time; at 4 degrees C or 1 degree C, the decline is still slower. Only a small contribution toward
adenosine triphosphate maintenance comes from
creatine phosphate, since
creatine phosphate,
inorganic phosphate, and total
creatine levels in the appendage are low (less than 2 mumol.gm-1 tissue wet weight). Glycolysis is active at all temperatures; the rate of glycolysis correlates positively with increasing temperature.
Adenosine triphosphate generated by glycolysis falls just short of demand at all temperatures, but the difference is small at 1 degree and 4 degrees C. These studies lead us to conclude that the relatively poor recovery of contractile response of human atrial trabeculae, together with
contracture reported previously at lower temperatures (1 degree and 4 degrees C), is not due to a failure to maintain
adenosine triphosphate levels.