The biochemical mechanisms by which macrophages become activated to the tumoricidal state are poorly understood. To investigate the role of calcium in this process, the effect of calcium channel blockers and calmodulin antagonists on the acquisition of tumoricidal properties by macrophages activated by a number of different agents was examined. Activation of thioglycollate-stimulated C57BL/6 mouse peritoneal macrophages by macrophage activation factor (MAF) plus LPS, IFN-γ plus LPS or the calcium ionophore, A23187, was inhibited in a doseependent fashion by the calcium channel blockers nifedipine and verapamil. These agents blocked the influx of 45Ca into macrophages activated by MAF plus LPS. Macrophage activation was also inhibited by chlorpromazine, W-7, and calmidazolium at concentrations known to perturb calmodulin function. The data suggest that activation of macrophages to the tumoricidal state is a calcium-dependent process involving the participation of calcium-regulated biochemical reactions whose activities can be modulated by pharmacological agents that frustrate transmembrane calcium fluxes and/or inhibit calmodulin function.
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