Changes of intracellular sodium T2 relaxation times during ischemia and reperfusion in isolated rat hearts

The effect of ischemia and reperfusion on transverse relax ation (T2) of intracellular Na+ (Na+i) was measured with 5‐min time resolution in isolated rat hearts. Nai T2 relaxation was biexponential with 28 ± 7% fast (T2f)and 72 ± 7% slow (T2s) decay. This ratio was constant throughout the protocol. Dur ing 20 min of ischemia, Nai T2s increased from 18.9 ± 2.7 ms to 26.4 ± 1.1 ms (P < 0.001), whereas T2f 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). T2s and Na+i declined again during reperfusion. Changes in T2s relaxation correlated significantly (r = 0.73, P < 0.001) with the time course of Na+i.