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Diffusional Water Permeability of Bovine Erythrocytes: A Pulse Nuclear Magnetic Resonance Study

Gojmir Lahajnar ; J. Stefan Institute, University of Ljubljana, 61000 Ljubljana, Slovenia

Puni tekst: engleski pdf 24.088 Kb

str. 191-200

preuzimanja: 212



A pulse nuclear magnetic resonance (NMR) technique is employed to study the temperature dependence of the diffusional water exchange time texch 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 of the erythrocyte suspension. The semi-log plots of Xcxch versus inverse absolute temperature for both normal and mercurial treated erythrocytes are straight lines, implying that one activation energy (Fa) determines the rate of transmembrane diffusional water transport in the whole temperature range studied (5-40 °C). For normal erythrocytes, the value Fa of 20.4 kJ/mol is similar to that for selfdiffusion of water (Fa = 19.3-20.1 kJ/mol). The value Xcxch = 12.5 ms, obtained for normal bovine erythrocytes at 20 °C, corresponds to the cell membrane diffusional water permeability coefficient Pd of 3.6x 10-3 cm/s. This is similar to the range of room temperature Pd between 3.3 and 4.7x 10-3 cm/s, deduced recently for fresh normal human erythrocytes. The data for p-MB treated erythrocytes display a lengthening of Texch and increased Fa of 29.0 kJ/mol. This Fa value and a permeability coefficient Pd of 2.6xl0~3 cm/s at 20 °C, if compared to the corresponding permeability data for artificial lipid bilayer membranes, indicate either only partial inhibition of the mercurial sensitive part of 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.

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