Evaluation of phosphate and HEPES buffers for study of erythrocyte rheology

Measurement of erythrocyte deformability is influenced by erythrocyte mean cell volume and mean cell haemoglobin concentration. Buffers used in rheological studies should therefore cause minimal alteration to these erythrocyte indices. For the study of human erythrocytes, the optimal concentration of phosphate in phosphate buffered saline was found to be 50 mmol/l at pH 7.4 and osmolality 290 mmol/kg. HEPES buffered saline (HEPES concentration 5-40 mmol/l, pH 7.4, osmolality 290 mmol/kg) also maintained satisfactory erythrocyte indices. Both buffers can be recommended for studies of erythrocyte rheology although the temperature dependence of the dissociation constant of HEPES necessitates strict control of the working temperature.