Three-dimensional Rb-87 NMR imaging and spectroscopy of K+ fluxes in normal and postischemic pig hearts

K+ uptake rates were measured in the anterior (An) and posterior (Pos) LV w alls of pig hearts before and after regional ischemia and reperfusion using Rb+ as a K+ congener and 3D Rb-87 NMR imaging acid spectroscopy as detecti on methods. The hearts were perfused by the Langendorff method with Krebs-H enseleit (KH) buffer and loaded with Rbi (4.7 mM, Rb-KH) after 120-min isch emia and 60-min reperfusion, A second protocol involved Rb+ loading prior t o ischemia, Ischemia was produced by occlusion of the left anterior descend ing artery, which after 110 min of reperfusion resulted in infarction in th e An wall (24 +/- 6% of the LV mass) determined by triphenyltetrazolium chl oride staining. At the end of reperfusion pressure-rate product and oxygen consumption rate decreased to 58 +/- 10 and 74 +/- 4% of their preischemic values, respectively. Phosphocreatine, ATP, and intracellular pH (pHi), mea sured by P-31 NMR spectroscopy in the infarcted area, decreased to 59 +/- 1 7, 32 +/- 6%, and 6.7 +/- 0.36 (from 7.05 +/- 0.13), respectively. Serial 8 7Rb images were acquired according to both protocols. Rate constants (k x 1 0(3), min(-1)), relative amount of intracellular Rb+ (A, %) and relative fl uxes (F = kA, %/min) for the An and Pos walls were determined from the imag es, Before ischemia, F and k were comparable in the Pos and An walls, Ische mia F reperfusion decreased F in the An wall (from 4.4 +/- 0.3 to 1.4 +/- 0 .85) due to a decrease in A (20 vs, 73) and increased F in Pos wall (from 3 .2 +/- 0.6 to 6.6 +/- 0.23) due to an increase in k (from 42 +/- 3 to 93 +/ - 6), The intensities of the Rb images correlated with the Rbi content meas ured in tissue samples. Published 2000 Wiley-Liss, Inc.(dagger).