DIFFUSIONAL WATER PERMEABILITY OF BOVINE ERYTHROCYTES - A PULSE NUCLEAR-MAGNETIC-RESONANCE STUDY

A pulse nuclear magnetic resonance (NMR) technique is employed to study the temperature dependence or the diffusional water exchange time tau(exch) for normal and p-hydroxymercuribenzoate (p-MB) treated bovine erythrocytes. The method is based on measurements of the proton NMR transverse relaxation function of water exchange between the diamagnetic intracellular space and the paramagnetically doped extracellular solution or the erythrocyte suspension. The semi-log plots of tau(exch) versus inverse absolute temperature for both normal and mercurial treated erythrocytes are straight lines, implying that one activation energy (E(a)) determines the rate of transmembrane diffusional water transport in the whole temperature range studied (5-40-degrees-C). For normal erythrocytes, the value E(a) or 20.4 kJ/mol is similar to that for selfdiffusion of water (E(a) = 19.3-20.1 kJ/mol). The value tau(exch) = 12.5 ms, obtained for normal bovine erythrocytes at 20-degrees-C, corresponds to the cell membrane diffusional water permeability coefficient P(d) or 3.6 x 10(-3) cm/s. This is similar to the range or room temperature P(d) between 3.3 and 4.7 x 10(-3) cm/s, deduced recently for fresh normal human erythrocytes. The data for p-MB treated erythrocytes display a lengthening of tau(exch) 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 the corresponding permeability data for artificial lipid bilayer membranes, indicate either only partial inhibition of the mercurial sensitive part or the membrane diffusional water permeability, possibly as a result of poor accessibility of the functionally important transmembrane protein SH-groups to p-MB, or >>complete<< inhibition plus new leaks.