Calcium is required for PMA induced superoxide release from human neutrophils

Regulation of superoxide production in neutrophils: role of calcium influx

Upon stimulation, activation of NADPH oxidase complexes in neutrophils produces a burst of superoxide anions contributing to oxidative stress and the development of inflammatory process. Store-operated calcium entry (SOCE), whereby the depletion of intracellular stores induces extracellular calcium influx, is known to be a crucial element of NADPH oxidase regulation. However, the mechanistic basis mediating SOCE is still only partially understood, as is the signal-coupling pathway leading to modulation of store-operated channels. This review emphasizes the role of calcium influx in the control of the NADPH oxidase and summarizes the current knowledge of pathways mediating this extracellular calcium entry in neutrophils. Such investigations into the cross-talk between NADPH oxidase and calcium might allow the identification of novel pharmacological targets with clinical use, particularly in inflammatory diseases.

Exposure of blood to biomaterial surfaces liberates substances that activate polymorphonuclear granulocytes

Human whole blood, anticoagulated or not, was exposed to hydrophilic glass surfaces or methylated hydrophobic glass surfaces under saline cover. Platelet-poor plasma or serum was prepared after 10 minutes of exposure, measured in respect to complement activation, and transferred to a suspension of granulocytes, which acted as bioprobes. The granulocytes were prepared from blood, anticoagulated with ethylenediaminetetraacetic acid, and evaluated regarding intracellular Ca2+ concentration (Calcium Green-1 fluorescence), integrin expression (CD-11b immunohistochemistry), respiratory burst (chemiluminescence), and priming (increase in N-formyl-methionyl-leucyl-phenylalanine-induced respiratory burst). The results indicate that humoral factors formed during the surface exposure of blood were able to activate the probe granulocytes. The exposure to hydrophilic surfaces led to a calcium transient three times the magnitude of that of hydrophobic surfaces. This response could be blocked by the presence of heparin during the blood-surface exposure but was not affected by the addition of heparin to the probe granulocytes. Hirudin, a specific thrombin blocker, had no effect. The exposure to hydrophobic surfaces led to complement activation in serum that induced priming and respiratory burst of the probe granulocytes. In conclusion, the study provides evidence that hydrophilic-hydrophobic surface treatment significantly affects the immediate inflammatory response of a blood-biomaterial interaction that is moderated by the presence of heparin.

Generation of hydroxyl radicals by polymorphonuclear neutrophils during exposure to direct current and iron

Human polymorphonuclear neutrophils were exposed to direct output current of 3 or 5 mA at either 300 or 500 V for 1 h in the presence and absence of iron. The current density was 25 or 40 nA/cm2. The formation of free oxygen radicals was measured as breakdown products from deoxyribose and methional. The cells were shown to generate oxygen radicals on electrical stimulation. A physiological concentration of iron enhanced radical formation, but OH. was also formed in the absence of added iron. The most pronounced stimulation was seen at output current 5 mA and 500 V.

The suppression of macrophage secretion by calcium blockers and adenosine

In an effort to examine the effects of calcium blockers and adenosine on superoxide, hydrogen peroxide, and nitrite secretions by mouse peritoneal macrophages, we have utilized the phenol red method, the superoxide dismutase-inhibitable reduction of ferricytochrome c method, and the Griess reagent method to test products after treating periodate-elicited mouse peritoneal macrophages with verapamil, nifedipine, and adenosine. The results show that after treating the macrophages with chemicals 10 minutes before adding PMA (100 ng/ml), all three chemicals inhibited superoxide (O2-) and hydrogen peroxide (H2O2) secretions dose-dependently, yet they failed to suppress macrophage reactive oxygen intermediates (ROI) after a 24 hour treatment. On the other hand, calcium blockers, verapamil and nifedipine, could reduce nitrite secretion (NO2-), while adenosine did not show the ability to inhibit NO2-. This indicates that calcium, as a secondary messenger, is important for the production of ROI and RNI. The reason behind the loss of the ability to suppress macrophage ROI production in a 24 hour treatment remains unexplored.