Rubidium-87 magnetic resonance spectroscopy and imaging for analysis of mammalian K+ transport

✍ Scribed by Valery V. Kupriyanov; Marco L. H. Gruwel

• Book ID: 102541338
• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 315 KB
• Volume: 18
• Category: Article
• ISSN: 0952-3480
• DOI: 10.1002/nbm.892

✦ Synopsis

This review summarizes results 87 Rb MRS/I studies of K þ transport in mammalian cells, organs and in vivo. It provides a brief description of K þ transport systems, their interactions with Rb þ and evidence that Rb þ is a best K þ congener. 87 Rb MR studies have focused mostly on isolated perfused rat and pig hearts and to a lesser extent on kidney, skeletal muscle, salivary gland and red blood cells. The method has been used for three purposes: measurements of kinetics of unidirectional Rb þ uptake and efflux and steady-state Rb þ levels. In cardiovascular studies Rb þ has been used in the absence of shift reagent taking advantage of the predominantly intracellular Rb þ /K þ distribution ( $ 20:1). Pharmacological analysis of Rb þ uptake and efflux allowed assessment of the contributions of various transporters to the total Rb þ fluxes in rat hearts. It was confirmed that Na þ /K þ ATPase is responsible for the majority of K þ influx since Rb þ uptake is 80% ouabain-sensitive and dependent on the intracellular [Na þ ]. Energy deprivation caused by low-flow ischemia or metabolic inhibition reduced Rb þ uptake rate. Under normal conditions, Rb þ efflux is mediated mainly by voltage-gated K þ channels with a small contribution from the K þ /Na þ /2Cl À cotransporter. Intracellular alkalosis and osmotic swelling stimulated Rb þ efflux by activation of the putative K þ /H þ antiporter. Activity of ATP-sensitive K þ (K ATP ) channels was revealed by metabolic (2,4-dinitrophenol, ischemia) or pharmacological (K ATP opener, P-1075) stimulation of Rb þ efflux, which was reversed by the K ATP blocker, glibenclamide. Mitochondrial K þ transport was evaluated in hearts with saponinpermeabilized myocytes and under hypothermic conditions.

Three-dimensional (3-D) spectroscopic MRI of isolated beating pig hearts has been used to obtain time series of Rb þ maps of normal and ischemic/infarcted hearts, which showed lower image intensity in the damaged area. Kinetics of Rb þ uptake in the ischemic areas depended on both regional flow and metabolism. The adrenergic agonist dobutamine stimulated Rb þ uptake in normal areas and did not affect uptake in ischemic areas. Drugs that may affect passive Rb þ transport (bumetanide, pinacidil, glibenclamide) did not change Rb þ uptake either in the normal or ischemic zones. 87 Rb-MRI was also able to localize ischemia and infarction in blood-perfused hearts. 87 Rb MRS/I is an excellent non-invasive research tool for studies of K þ transport in isolated organs and in vivo.