Contribution of intracellular Ca2+ stores to Ca2+ signaling during chemokinesis of human neutrophil granulocytes

Extracellular agonists increase the cytosolic free Ca2+ concentration ([Ca2+]c) by Ca2+ influx and by stimulating Ca2+ release from intracellular stores, mainly the endoplasmic reticulum and to a lesser extent also later compartments of the secretory pathway, particularly the Golgi. The Golgi takes up Ca2+ via Sarco/Endoplasmic Reticulum Ca2+ATPases (SERCAs) and the Secretory-Pathway Ca2+ATPases (SPCAs). The endogenous expression of SERCAs and SPCAs neutrophils was demonstrated by Western blotting and immunocytochemistry. Up till now, all cytosolic Ca2+ transients due to intracellular Ca2+ release have been found to originate from SERCA-dependent stores. We found that human neutrophils also present Ca2+ release from a SERCA-independent store. Changes in [Ca2+]c of neutrophils were investigated during chemokinesis induced by chemotactic factors in Ca2+-free solution with and without the SERCA-specific inhibitor thapsigargin. Using N-formyl-methionyl-leucyl-phenylalanine or interleukin-8 as agonists, Ca2+ release from intracellular stores was observed in respectively about 40% and 20% of the neutrophils pre-treated with Ca2+-free solution and thapsigargin. In the latter condition, 20–30% of the cells preserved migratory behaviour. These results indicate that both SERCA-dependent and SERCA-independent (presumably SPCA-dependent) intracellular Ca2+ stores contribute to Ca2+ signaling during chemokinesis of human neutrophil granulocytes.