A PULSE NMR-STUDY OF WATER EXCHANGE ACROSS THE ERYTHROCYTE-MEMBRANE

A pulse nuclear magnetic resonance (NMR) technique is employed to study the temperature dependence (5-40-degrees-C) of the diffusional water exchange time tau(exch) for normal and p-hydroxymercuribenzoate (p-HMB) treated bovine erythrocytes. The Arrhenius plot of tau(exch) for normal erythrocytes implies the activation energy E(a) of 20.4 kJ/mol, similar to that for self-diffusion of water (E(a) = 19.3 - 20.1 kJ/mol), and the value tau(exch) of 12.5 ms at 20-degrees-C corresponds to the cell membrane diffusional water permeability coefficient Pd of 3.6 X 10(-3) cm/s. The data for p-HMB treated cells display lengthening of tau(exch) (i.e., T(exch) = 173 ms at 20-degrees-C) and increased E(a) of 29.0 kJ/mol. This E(a) value and a permeability coefficient P(d) of 2.6 x 10(-3) cm/s at 20-degrees-C, if compared to corresponding data for artificial lipid bilayer membranes, indicate either incomplete closure of the specialized water-selective protein channels on binding of p-HMB to their SH-groups, or complete channel closure plus new leaks.