Potassium transport in Langendorff‐perfused mouse hearts assessed by 87 Rb 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 + efflux 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 (∼30% faster than in the rat heart). The ATP‐sensitive potassium channel opener, P‐1075 (5 μM), and mitochondrial uncoupler, 2,4‐dintrophenol (50 μM), activated Rb + efflux from mouse hearts by ∼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. © 2005 Wiley‐Liss, Inc.