Water exchange between red cells and plasma. Measurement by nuclear magnetic relaxation.

Water exchange between human red blood cells and the plasma phase was measured by water proton nuclear magnetic resonance relaxation in the presence of low concentrations of Mn(II) and by 17O relaxation of H217O in the absence of added Mn(II). The results were analyzed as a classic case of two-compartment exchange. The half-life for cell water at 25 degrees C was found to be 15 ms +/- 2 ms, longer than the time determined by other techniques. The T1 of the hemoglobin protons in the red cell and the volume of exchangeable water were also measured. The method appears to be a sensitive tool for the study of membrane permeability to water and other small molecules undergoing rapid exchange.