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

Abstract

K+ uptake rates were measured in the anterior (An) and posterior (Pos) LV walls of pig hearts before and after regional ischemia and reperfusion using Rb+ as a K+ congener and 3D 87Rb NMR imaging and spectroscopy as detection methods. The hearts were perfused by the Langendorff method with Krebs-Henseleit (KH) buffer and loaded with Rb+ (4.7 mM, Rb-KH) after 120- min ischemia and 60-min reperfusion. A second protocol involved Rb+ loading prior to ischemia. Ischemia was produced by occlusion of the left anterior descending artery, which after 110 min of reperfusion resulted in infarction in the An wall (24 ± 6% of the LV mass) determined by triphenyltetrazolium chloride 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), measured by 31P NMR spectroscopy in the infarcted area, decreased to 59 ± 17, 32 ± 6%, and 6.7 ± 0.36 (from 7.05 ± 0.13), respectively. Serial 87Rb images were acquired according to both protocols. Rate constants (k x 103, min-1), relative amount of intracellular Rb+ (A, %) and relative fluxes (F = kA, %/min) for the An and Pos walls were determined from the images. Before ischemia, F and k were comparable in the Pos and An walls. Ischemia + 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 Rb+ content measured in tissue samples.