Time-Dependent Diffusion of Water in a Biological Model System

• Published in: Proceedings of the National Academy of Sciences - PNAS 1994-02, Vol.91 (4), p.1229-1233
• Main Authors: Latour, Lawrence L., Svoboda, Karel, Mitra, Partha P., Sotak, Christopher H.
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Biological Transport; Brain Ischemia; Cattle; Cell Membrane Permeability; Cell membranes; Cell Size; Cellular biology; Diffusion; Diffusion coefficient; Erythrocyte membrane; Erythrocyte Membrane - metabolism; Erythrocytes; Extracellular fluid; Fluid permeability; Fundamental and applied biological sciences. Psychology; General aspects, investigation technics, apparatus; Humans; Magnetic Resonance Spectroscopy - methods; Material concentration; Models, Biological; Models, Theoretical; Physics; Porous materials; Surface Properties; Time dependence; Time Factors; Tissues, organs and organisms biophysics; Ungulates; Water - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.91.4.1229

Packed erythrocytes are ideally suited as a model system for the study of water diffusion in biological tissue, because cell size, membrane permeability, and extracellular volume fraction can be varied independently. We used a pulsed-field-gradient spin echo NMR technique to measure the time-dependent diffusion coefficient D(t) in packed erythrocytes. The long-time diffusion constant, Deff, depends sensitively on the extracellular volume fraction. This may explain the drop in Deffduring the early stages of brain ischemia, where just minutes after an ischemic insult the extra-cellular volume in the affected region of the brain is significantly reduced. Using an effective medium formula, we estimate the erythrocyte membrane permeability, in good agreement with measurements on isolated cells. From the short-time behavior of D(t), we determine the surface-to-volume ratio of the cells,$\thickapprox$(0.72 μm)-1.