The influence of calcium on the deformability of human granulocytes

Experiments were carried out to determine the importance of extra- and intracellular calcium for the deformability of granulocytes during filtration tests. At low calcium concentration (0.1 mM), granulocytes are more deformable than at the physiological free-calcium concentration of 1.25 mM. Increasing calcium concentrations up to 10 mM do not further impair the deformability. Parallel measurements of the intracellular calcium concentration by means of the fura fluorescence method were performed to explain this. Extracellular calcium concentrations between 1.25 mM and 10 mM had no influence on the intracellular calcium level. A lower extracellular calcium concentration (0.1 mM), however, decreased the intracellular calcium level. Therefore, the measurements of the intracellular calcium concentrations are consistent with the deformability results. Studies with the calcium entry blocker nifedipine suggested that a low intracellular calcium improves the deformability of granulocytes. It is concluded; (i) the physiological calcium concentration of 1.25 mM is stressful for isolated granulocytes, and (ii) the intracellular calcium level plays a crucial role in granulocyte deformability, i.e. the lower the intracellular calcium concentration the greater the deformability.