Effects of ischemia on intracellular rubidium in pig and rat hearts: Rb-87NMR imaging and spectroscopic study

Rb-87 MR imaging and spectroscopy were used to study the effects of ischemi a on the properties of K+ in cardiac tissue. Isolated pig and rat hearts pe rfused by the Langendorff method with Krebs-Henseleit buffer were preloaded with Rb+. Ischemia (Isc) was induced by 120-min occlusion of the left ante rior descending artery in the pig hearts or by stopping perfusion for 33 mi n in the rat hearts. Serial Rb-87 MR images or spectra from the anterior (A n) LV wall of pig hearts were acquired continuously. The intensities of the Rb images of the An and posterior (Pos) walls were similar and stable duri ng the first 45 min of ischemia. The intensity of signal from the An wall ( Isc) then gradually increased by 60 +/- 8% relative to the preischemic valu e (vs. 31 +/- 5% increase in Pos wall) and necrosis (19 +/- 5% of the LV wa ll mass) developed upon reperfusion. The Rb+ content was lower in the ische mic (An) than in the normal (Pos) area (22.3 +/- 3 vs. 28.4 +/- 1.3 mmol/g wet wt). A similar pattern was observed in the peak heights of Rb-87 spectr a from the An wall, which increased by 40 +/- 16% (vs, 21 +/- 11% in contro l) due to a 12% decrease in the apparent Rb linewidth (LW) and a 24 +/- 14% increase in the peak area. The Rb peak comprised narrow (297 +/- 21 Hz) an d broad (1098 +/- 40 Hz, 59 +/- 3% of total area) Lorentzian components. Th e LW of the broad component decreased by 14%, while the narrow component di d not change markedly. In the rat hearts ischemia caused a 33 +/- 4% increa se in the Rb-87 peak height as a result of peak narrowing (13 +/- 1%), and an increase in peak area (17 +/- 5%). The decreases in LW and increases in Rb+ visibility can be explained by an increase in Rb+ mobility caused by di splacement of Rb+ from anionic binding sites by H+ (ischemic acidosis) and changes in intracellular compartmentalization of Rb+. Magn Reson Med 44: 19 3-200, 2000, (C) 2000 Wiley-Liss, Inc.