Measurement of rapid membrane permeation in cell suspensions by application of a generalized capillary method

An improved version of the capillary technique for the determination of diffusion coefficients has been developed as a simple method of measuring membrane permeabilities of single cells suspended at relative densities between 0.70 and 0.97. A new, generalized theoretical formulation to describe the diffusion process of a solute in a composite system was derived using a series-parallel-pathway model with explicit consideration of the diffusion pathways inside and between the cells. This renders the technique insensitive to unstirred layer effects. Any single cell population of known size distribution may be investigated. High permeabilities (above 5.10(-3) cm/s) can be measured with the greatest precision, but lower permeabilities, down to a limit of about 5.10(-4) cm/s, may also be determined by the method. Measurements in erythrocyte suspensions have been made using non-electrolytes such as hexanol, water and ethylene glycol as test solutes. The permeabilities obtained agree with the values obtained by much more sophisticated equipment. Cell shape was shown to be without significant influence on the permeability data obtained. The procedure may become of particular interest for measurement of suspensions of membrane vesicles.