Potassium-39 nuclear magnetic resonance observation of intracellular potassium without chemical shift reagents during metabolic inhibition in the isolated perfused rat heart.

The intracellular potassium content of perfused rat heart was measured by potassium-39 nuclear magnetic resonance (NMR) spectroscopy at 33 degrees C with an inversion recovery technique based on the fact that the spin-lattice relaxation time (T1) of the intracellular potassium (8.3 msec at 8.45 T) is much faster than that of the extracellular potassium (68 msec). Intracellular potassium decreased to 60.2 +/- 4.3% of the control level (mean +/- SEM, n = 6) at 40 minutes from the start of metabolic inhibition (2 mM cyanide, 0 mM glucose). Removal of cyanide restored intracellular potassium to 94.2 +/- 3.9% at 30 minutes from the restart of oxidative metabolism. The cumulative potassium loss was determined from the flow rate and potassium concentration of the coronary effluent, which reached 139 +/- 12 mumol/g dry wt during 40 minutes of metabolic inhibition. This value was calculated as 41.8% of intracellular potassium in the control heart and agreed with the decrement of intracellular potassium measured by NMR. During the metabolic inhibition and recovery period, a linear correlation was observed between the changes in 39K NMR-observed intracellular potassium and the cumulative potassium loss. The present results evaluate the inversion recovery technique as a method to successfully monitor the myocardial intracellular potassium.