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 responses within a cell. A potential but previously unexplored mechanism for the generation of gradients of [Ca²⁺]_i is the accumulation of Ca²⁺ stores at the site of Ca²⁺ action. The distribution of the Ca²⁺ store markers Ca²⁺-dependent adenosine triphosphatase and catreticulin was investigated in resting and phagocytosing human neutrophils. Both proteins showed an evenly distributed fine granular pattern in nonphagocytosing cells, but became markedly concentrated in the filamentous actin-rich 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.