Water Exchange Kinetics in the Isolated Heart Correlate with Na+/K+ ATPase Activity: Potentially High Saptiotemporal Resolution in Vivo MR Access to Cellular Metabolic Actiivity

Yajie Zhang¹, James A. Balschi¹

The extracellular relaxation agent, GdDTPA^2- was used to distinguish intra- and extracellular ¹H₂O signals by altering their T₁ values. Equilibrium trans-plasma membrane water exchange kinetics were quantified using two-site-exchange analysis to obtain the mean intracellular water life time (_i ). Our studies found that _i^-1 (water exchange) correlated with Na⁺/K⁺ ATPase activity in isolated perfused rat hearts. Thus, _i^-1 acts as a biomarker for the cellular membrane transport activity. Potentially _i^-1 is altered in pathological states. _i can be determined from pharmacokinetic analyses of in vivo ¹H₂O DCE-MRI studies. These findings could enable high resolution functional metabolic imaging.