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

The effect of ischemia and reperfusion on transverse relaxation (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. During 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(+).