CALCIUM OSCILLATIONS INDEX THE EXTENT OF CALCIUM LOADING AND PREDICT FUNCTIONAL RECOVERY DURING REPERFUSION IN RAT MYOCARDIUM

Delayed recovery of contractile function after myocardial ischemia may be due to prolonged recovery of high-energy phosphates, persistent acidosis, increased inorganic phosphate, and/or calcium loading. To examine these potential mechanisms, metabolic parameters measured by 31P nuclear magnetic resonance spectroscopy, and spontaneous diastolic myofilament motion caused by sarcoplasmic reticulum-myofilament calcium cycling indexed by the scattered light intensity fluctuations (SLIF) it produces in laser beam reflected from the heart, were stuided in isolated atrioventricularly blocked rat hearts (n = 10) after 65 min of ischemia at 30°C. All metabolic parameters recovered to their full extent 5 min after reperfusion. Developed pressure evidenced a small recovery but then fell abruptly. This was accompanied by an increase in end diastolic pressure to 37 ± 5 mm Hg and a fourfold increase in SLIF, to 252 ± 58% of baseline. In another series of hearts initial reperfusion with calcium of 0.08 mM prevented the SLIF rise and resulted in improved developed pressure (74 ± 3% vs. 39 ± 13% of control), and lower cell calcium (5.9 ± 3 vs. 10.3 ± 1.4 μmol/g dry wt). Thus, during reperfusion, delayed contractile recovery is not associated with delayed recovery of pH, inorganic phosphate, or high-energy phosphates and can be attributed, in part, to an adverse effect of calcium loading which can be indexed by increased SLIF occurring at that time.