ABSTRACT
The measurement of rapid solute exchange through biological membranes by conventional techniques becomes increasingly difficult in the range of high permeabilities. Bulk diffusion techniques for the determination of high permeabilities might be of particular relevance for measurements in small vesicles because in this size range the conventional tracer flux techniques cannot be used. The self-diffusion of water is measured by using tritiated water as a tracer. Most methods used to measure the rapid transport of highly permeable solutes such as water or other small nonelectrolytes suffer from the problem of unstirred layers which may affect the transfer rate to a nonnegligible extent. As a test, the permeation of water across human red blood cell membranes was investigated. The improved version of the capillary method is well adapted to the measurement of the high permeability of water and even higher transfer rates. Hemoglobin solutions are prepared by osmotic lysis of washed red blood cells in distilled water.
