Activation Mechanism of NADPH Oxidase by SDS in Intact Guinea Pig Neutrophils

It is well known that sodium dodecyl sulfate (SDS) activates NADPH oxidase in a cell-free system independently of protein kinase C (PKC). However, in intact neutrophils, direct evidence has never been presented to show that O−2 production by SDS is actually due to the NADPH oxidase activation observed in the cell-free system. So, in this paper, we investigated the activation mechanism by SDS in intact guinea pig neutrophils. We previously reported that hypotonic treatment reversibly enhanced O−2 production stimulated by PKC activators in intact neutrophils (M. Hiura et al., 1991, Arch. Biochem. Biophys. 291, 31-37). In this paper, SDS also significantly stimulated O−2 production in the intact cells under the hypotonic condition. This enhancement was gradual and was PKC inhibitor resistant. Furthermore, phosphorylation of the 46-kDa protein, one of cytosolic activation factors, was not detected by autoradiography of two-dimensional electrophoresis. Translocation of cytosolic activation factors was demonstrated by a decrease in the activity of the factors remained in the cytosol. In the presence of SDS, addition of 1-oleoyl-2-acetylglycerol, a PKC activator, further enhanced O−2 production and translocation of the cytosolic activation factors. On the other hand, SDS remarkably increased membrane fluidity in intact neutrophils as well as in the cell-free system. These results indicate that activation of NADPH oxidase by SDS in intact neutrophils seems to be partly due to the same mechanism observed in cell-free activation, and that SDS alone slightly activates the oxidase and other stimulation, such as hypotonic and/or PKC activator treatments, is required for significant activation. The increase in the membrane fluidity may be one of the activation mechanisms of NADPH oxidase by SDS.