A novel H+ conductance in eosinophils: Unique characteristics and absence in chronic granulomatous disease

Efficient mechanisms of H+ ion extrusion are crucial for normal NADPH oxida se function. However, whether the NADPH oxidase-in analogy with mitochondri al cytochromes-has an inherent Hf channel activity remains uncertain: elect rophysiological studies did not find altered H+ currents in cells from pati ents with chronic granulomatous disease (CGD), challenging earlier reports in intact cells. In this study, we describe the presence of two different t ypes of H+ currents in human eosinophils. The "classical" H+ current had pr operties similar to previously described H+ conductances and was present in CGD cells. In contrast, the "novel" type of H+ current had not been descri bed previously and displayed unique properties: (a) it was absent in cells from gp91- or p47-deficient CGD patients; (b) it was only observed under ex perimental conditions that allowed NADPH oxidase activation; (c) because of its low threshold of voltage activation, it allowed proton influx and cyto solic acidification; (d) it activated faster and deactivated with slower an d distinct kinetics than the classical H+ currents, and (e) it was similar to 20-fold more sensitive to Zn2+ and was blocked by the histidine-reactive agent, diethylpyrocarbonate (DEPC). In summary, our results demonstrate th at the NADPH oxidase or a closely associated protein provides a novel type of H+ conductance during phagocyte activation. The unique properties of thi s conductance suggest that its physiological function is not restricted to H+ extrusion and repolarization, but might include depolarization, pH-depen dent signal termination, and determination of the phagosomal pH set point.