NMR spectroscopic characterization of sarcolemmal permeability during myocardial ischemia and reperfusion

N. ASKENASY, A. VIVI, M. TASSINI, G. NAVON, D. L. FARKAS. NMR Spectroscopic Characterization of Sarcolemmal Permeability During Myocardial Ischemia an d Reperfusion, Journal of Molecular and Cellular Cardiology (2001) 33, 1421 -1433, This study aims to characterize the pattern of membrane disintegrati on during myocardial ischemia and reperfusion. Intracellular volumes were m easured by H-1 and Co-59 NMR in isolated rat hearts during 10, 30 and 60 mi n of total ischemia and 30 min of reperfusion at normothermia. Perfusion wi th hypo-osmotic medium (210 mosm/l) increased intracellular water from 2.50 +/- 0.06 to 3.07 +/- 0.07 ml/g dry weight (P < 0.001) during pre-ischemia, Hypo-osmotic swelling decreased by 16 +/- 3, 32 +/- 6 and 44 +/- 11% of th e pre-ischemic value after 10, 30 and 60 min of ischemia (N.S., P < 0.005, P < 0.001) respectively. indicating that membrane permeabilization facilita ted efflux of osmolytes and counterbalanced the osmotic driving force for w ater influx. Hypo-osmotic swelling decreased during 30 min of reperfusion b y 18 +/- 5% in all groups (P < 0.0.005 v postischemia). The volume of distr ibution of the extracellular marker cobalticyanide increased by more than 3 .2 +/- 0.4 and 5.8 +/- 0.5% of the intracellular space after 30 and GO min of ischemia respectively (P < 0.001), and by an additional 2% after reperfu sion. During 30 min of reperfusion, hearts released 1.6 +/- 0.2 and 3.2 +/- 0.4% of the intracellular creatine kinase contents after 30 and 60 min of ischemia, respectively (P < 0.001). In addition to the correlation between ischemia duration and membrane permeability, evident from the analysis of e ach probe, the data showed a progressive increase in severity of membrane i njury over time and permeabilization to larger molecules, Na-23 NMR spectro scopy in conjunction with an extracellular shift reagent (SR) showed format ion of a resonance at an intermediate chemical shift in between the intra a nd extracellular Na+ peaks, suggesting penetration of SR into cells with di srupted membranes, The constant chemical shift and narrow line shape of thi s resonance, characteristic of a homogeneous chemical environment, suggeste d that the distribution of SR was contained within the cytosol of cardiomyo cytes. Mie propose that sarcolemmal membranes are gradually permeabilized t o larger molecules by ischemia, and the evolving chemical instability is sp atially contained within the myocyte. (C) 2001 Academic Press.