A phosphorus-31 nuclear magnetic resonance study of myocardial ATP content during postischemic low calcium...

Postischemic reperfusion injury can be modified by transient low calcium (Ca2+) reperfusion, although the data on the optimal [Ca2+] are controversial. High-energy phosphates and contractile function of isolated perfused rat hearts (37 degrees C, 300 beats/min) were studied simultaneously during global ischemia (30 min) and reperfusion (10 min at [Ca2+] = 1.3, 0.05, 0.1, 0.3, 0.5 and 0.7 mmol/l, followed by 20 min at [Ca2+] = 1.3 mmol/l), using phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy. Reperfusion with 1.3 mmol/l Ca2+ after 0.05 or 0.1 mmol/l Ca2+ largely abolished the recovery of ATP obtained during initial low Ca2+ reperfusion (calcium paradox effect). A [Ca2+] of 0.3 mmol/l was sufficiently high to prevent this detrimental effect; at the same time this concentration was sufficiently low to cause a substantial recovery of ATP, which was maintained upon switching to 1.3 mmol/l Ca2+. Recovery of ATP did not correlate with recovery of contractile function.