Intracellular Volume Measurement and Detection of Edema: Multinuclear NMR Studies of Intact Rat Hearts during Normothermic Ischemia

The present study describes the cell volume dynamics in intact rat hearts, during ischemia and after reperfusion. Cell volumes were measured in isolated hearts by either ¹³C or ⁵⁹Co NMR of mannitol or cobalticyanide, respectively, as extracellular markers and ¹H NMR of water as the aqueous space marker. A constant volume chamber was built inside a 15‐mm NMR tube; the contents of the chamber were measured with and without a heart. The intracellular volume of isolated rat hearts was estimated to be 2.45 ± 0.13 ml/g dry weight. In the perfused heart, adenosine triphosphate (ATP) and phosphocreatine (PCr) concentrations were calculated to be 12.2 ± 0.7 and 16.1 ± 1.0 mM, respectively. Consecutive volume measurements showed cell swelling of 16% during 30 min of ischemia, which was reduced at reperfusion to 7%. After 30 min of reperfusion, ATP and PCr concentrations were 4.5 ± 0.8 and 8.1 ± 0.9 mM. It is concluded that: (1) cell swelling is an ischemic event, which is partially reversed by reperfusion; and (2) continuous measurement of cell volumes provides intracellular molar concentrations of metabolites, which are the physiologically significant parameters.