Potassium transport in Langendorff-perfused mouse hearts assessed by 87Rb NMR spectroscopy

We studied the fluxes of a potassium congener (Rb+) in mouse hearts by (87) Rb MRS at 8.4T. The hearts were loaded with Rb+ by perfusion with Krebs-Henseleit buffer, in which 50% of K+ was substituted with Rb+. We initiated Rb+ eff lux by changing the perfusion medium to Rb+-free buffer. Spectra were acquired every 1.85 min, and the kinetics of Rb+ transport were analyzed by means of monoexponential fits. The rate constants of Rb+ uptake and efflux were 0.0680 +/- 0.0028 and 0.0510 +/- 0.0051 min(-1), respectively (similar to 30% faster than in the rat heart). The ATP-sensitive potassium channel opener, P-1075 (5 mu M), and mitochondrial uncoupler, 2,4-dintrophenol (50 mu M), activated Rb+ eff lux from mouse hearts by similar to 35%. The mechanisms responsible for the differences in Rb+ uptake and efflux under baseline conditions and stimulation, in comparison with rat hearts, are discussed. These data provide a background for studies of cardiac potassium transport in transgenic mouse strains. Magn Reson Med 53:1172-1176, 2005. (c) 2005 Wiley-Liss, Inc.