An Elevation in the Concentration of Free Cytosolic Calcium Is Sufficient to Activate the Oxidative Burst of Granulocytes Primed with Recombinant Human Granulocyte-Macrophage Colony-stimulating Factor

Abstract

In granulocytes harvested from human blood, an elevation of the cytosolic concentration of Ca2+ ions is by itself insufficient to activate the cell's respiratory burst. We report herein that, when granulocytes are "primed" by a 90-min preincubation with the recombinant human hemopoietic growth factor granulocyte-macrophage colony-stimulating factor (GM-CSFrh), elevation of the concentration of cytosolic Ca2+ ions ([Ca2+]i) becomes a more effective transduction signal capable of triggering the generation of substantial quantities of superoxide (O2-) anions by the cell. In these studies, we used four separate and independent maneuvers to induce elevation of [Ca2+]i: 1) depolarization of the cell's electrical potential through obliteration of the transmembrane Na+ and K+ gradients; 2) acidification of the cytoplasm using propionic acid; 3) addition of the calcium ionophore ionomycin; and 4) treatment of the cells with the monoclonal antibody to the C3bi receptor, PMN7C3. In all cases, elevation of [Ca2+]i through these manipulations resulted in the release of substantially greater quantities of O2- by GM-CSFrh-primed granulocytes than by unprimed, control cells. The generation of O2- was in all cases markedly reduced by chelation of either intracellular Ca2+ with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid or extracellular Ca2+ with [ethylene-bis(oxyethylenenitrilo)]tetraacetic acid. We conclude that during the process of GM-CSFrh priming, the metabolic assembly responsible for O2- anion production in the granulocyte becomes altered in such a way that a subsequent elevation in [Ca2+]i provides a potent signal for its activation.