Changes of intracellular sodium T 2 relaxation times during ischemia and reperfusion in isolated rat hearts

The effect of ischemia and reperfusion on transverse relax ation ( T 2 ) of intracellular Na + (Na + i ) was measured with 5‐min time resolution in isolated rat hearts. Na i T 2 relaxation was biexponential with 28 ± 7% fast (T 2f )and 72 ± 7% slow ( T 2s ) decay. This ratio was constant throughout the protocol. Dur ing 20 min of ischemia, Na i T 2s increased from 18.9 ± 2.7 ms to 26.4 ± 1.1 ms (P < 0.001), whereas T 2f did not change significantly (3.1 ± 1.8 versus 2.3 ± 1.6 ms during control), and Na+ i increased from 9.0 ± 1.0 to 19.5 ± 1.0 mmol/liter (P < 0.001). T 2s and Na + i declined again during reperfusion. Changes in T 2s relaxation correlated significantly (r = 0.73, P < 0.001) with the time course of Na + i .