REDISTRIBUTION OF INTRACELLULAR CA2+ STORES DURING PHAGOCYTOSIS IN HUMAN NEUTROPHILS

Subcellular gradients of cytosolic free Ca2+ concentration, [Ca2+](i), are thought to be critical for the localization of functional respons es within a cell. A potential but previously unexplored mechanism for the generation of gradients of [Ca2+](i) is the accumulation of Ca2+ s tores at the site of Ca2+ action. The distribution of the Ca2+ store m arkers Ca2+-dependent adenosine triphosphatase and calreticulin was in vestigated in resting and phagocytosing human neutrophils. Both protei ns showed an evenly distributed fine granular pattern in nonphagocytos ing cells, but became markedly concentrated in the filamentous actin-r ich cytoplasmic area around the ingested particle during phagocytosis. This redistribution began at early stages of phagocytosis and did not depend on an increase in [Ca2+](i). Thus, accumulation of Ca2+ stores in a restricted area of the cell may contribute to the generation of localized increases in [Ca2+](i).