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In human neutrophils, both changes in intracellular Ca2+ concentrations, [Ca2+ ]i , and activation of phosphatidylinositol-3 kinase (PtdIns3K) have been proposed to play a role in regulating cellular function induced by chemoattractants. In this study we have investigated the role of [Ca2+ ]i and its effector molecule calmodulin in human neutrophils. Increased [Ca2+ ]i alone was sufficient to induce phosphorylation of extracellular signal-regulated protein kinase 2 (ERK2), p38 mitogen activated kinase (p38 MAPK), protein kinase B (PKB) and glycogen synthase kinase-3α (GSK-3α). Inhibition of calmodulin using a calmodulin antagonist N -(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W7), did not effect N -formyl-methionyl-leucyl-phenylalanine (fMLP) induced ERK, p38 MAPK or GSK-3α phosphorylation, but attenuated fMLP induced PKB phosphorylation. PCR analysis of human neutrophil cDNA demonstrated variable expression of members of the Ca2+ /calmodulin-dependent kinase family. The roles of calmodulin and PtdIns3K in regulating neutrophil effector functions were further compared. Neutrophil migration was abrogated by inhibition of calmodulin, while no effect was observed when PtdIns3K was inhibited. In contrast, production of reactive oxygen species was sensitive to inhibition of both calmodulin and PtdIns3K. Finally, we demonstrated that chemoattractants are unable to modulate neutrophil survival, despite activation of PtdIns3K and elevation [Ca2+ ]i . Taken together, our data indicate critical roles for changes in [Ca2+ ]i and calmodulin activity in regulating neutrophil migration and respiratory burst and suggest that chemoattractant induced PKB phosphorylation may be mediated by a Ca2+ /calmodulin sensitive pathway in human neutrophils. [ABSTRACT FROM AUTHOR]