Permeability of human blood platelets to glycerol

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Abstract
The permeability of human platelets to glycerol was determined at 37°C, 25°C, and 0°C from the rate of change of cell volume after abrupt addition of 0.5 mol/liter glycerol in phosphate-buffered saline. Intracellular water volume was measured employing both tritiated water and a photometric method. Intracellular glycerol was measured employing tritiated glycerol. The glycerol permeability coefficient derived from the tracer cell volume data was 4.0 ± 0.7 × 10 −7 cm/s at 37°C, and 1.1 ± 0.4 × 10−7 cm/s at 25°C, and the photometric data gave a permeability coefficient of 5.4 ± 0.4 × 10−7 cm/s at 37°C. The activation energy between 23°C and 37°C for glycerol permeation was 19.8 kcal/mol. The cells were virtually impermeable to glycerol at 0°C. The minimum intracellular water volume attained after the addition of 0.5 mol/liter glycerol at 37°C determined by the photometric method was 47.8% of normal water volume, whereas the minimum water volume calculated assuming that glycerol exerted its full osmotic effect (i.e., σ = 1) was 45.6%. The reflexion coefficient was therefore assumed to be unity. Neither method of cell volume determination could be used with 1 or 2 mol/liter glycerol: adequate separation of the cells from the labeled medium could not be achieved in the tracer method; in the photometric method, it was apparent that transmittance (660 nm) was influenced by one or more variables in addition to cell volume.