Affiliations: Dept of Haematology | Helmholtz Instituut, Dept. Physics of Man, University of Utrecht | Dept. of Internal Medicine, University of Amsterdam. Dept. of Haematology, Univ. Hospital, G.03.647, P.O. Box 85500 GA Utrecht, The Netherlands
Abstract: Measurements of red cell deformability are usually performed in isotonic buffer solutions as suspending medium. However, in vivo, red cells are surrounded by plasma in which plasma proteins are present. In this study we investigated whether using plasma (anticoagulated with 1/10 vol. 110 mM trisodium citrate) instead of buffer (phosphate buffered saline solution) as the suspending medium gives rise to differences in the measured red cell deformability parameters. We used ektacytometry, the micropipette, the flow channel (both static and dynamic), and a Cell Transit Analyzer to study this effect. Where necessary, we added 1 g/l bovine serum albumin to prevent echinocyte formation, and poly-vinyl-pyrrolidone to increase the buffer viscosity to match that of plasma. Plasma was found to be a good alternative for buffer as suspending medium except for ektacytometric measurements. In ektacytometry, interactions between plasma components and the polymer added to increase the medium viscosity caused measurement artefacts. Comparison between the plasma and the buffer measurements using the other techniques showed a decreased red cell deformability in plasma. We found that in plasma membrane elasticity is decreased and membrane viscosity is increased compared with buffer (from micropipette and flow channel measurements) and a decreased filterability in plasma with the Cell Transit Analyzer. It is unclear whether the plasma composition or the buffer composition is responsible for the observed increased membrane viscosity and decreased membrane elasticity in plasma or, in other words, the decreased viscosity and increased elasticity in buffer. However, our results raise the question whether buffer is a good medium and whether deformability studies in general should be performed in plasma instead of in buffer.
