Treatment of the Macrophage-Like P388d.1 Cells with Bacterial Lipopolysaccharide and Interferon-Gamma Causes Longterm Alterations in Calcium Metabolism

The intracellular calcium concentrations ([Ca2+]i) of P338D.1 macrophage-like cells, activated with interferon-γ (IFN-γ) and/or bacterial lipopolysaccharide (LPS) were determined using fura-2/AM and ratiometric imaging techniques. Treatment of macrophages with IFN-γ and LPS resulted in significant downward shift in [Ca2+]i, 8, 16 and 24 h but not at 1 and 4 h after treatment. The decrease in [Ca2+]i also occurred when macrophages were treated with LPS only, but not after exposure of the cells to recombinant IFN-γ, indicating that LPS was an essential signal in the observed changes in [Ca2+]i of activated macrophages. The IFN-γ and/or LPS alteration in the [Ca2+]i, paralleled the in vitro nitric oxide production of the activated macrophages, 8, 16 and 24 h after treatment. The decrease in the [Ca2+]i may be caused by vigorous buffering and storing of Ca2+ by macrophages to below the normal resting quantities, following the reported transient increase in Ca2+ during the priming stage of macrophage activation. Thus, the downward shift in [Ca2+]I may play a physiological role in the activation processes of macrophages for antimicrobial responses.