A Novel H 1 Conductance in Eosinophils : Unique Characteristics and Absence in Chronic Granulomatous Disease

Efficient mechanisms of H 1 ion extrusion are crucial for normal NADPH oxidase function. However, whether the NADPH oxidase—in analogy with mitochondrial cytochromes—has an inherent H 1 channel activity remains uncertain: electrophysiological studies did not find altered H 1 currents in cells from patients with chronic granulomatous disease (CGD), challenging earlier reports in intact cells. In this study, we describe the presence of two different types of H 1 currents in human eosinophils. The “classical” H 1 current had properties similar to previously described H 1 conductances and was present in CGD cells. In contrast, the “novel” type of H 1 current had not been described previously and displayed unique properties: (a) it was absent in cells from gp91or p47-deficient CGD patients; (b) it was only observed under experimental conditions that allowed NADPH oxidase activation; (c) because of its low threshold of voltage activation, it allowed proton influx and cytosolic acidification; (d) it activated faster and deactivated with slower and distinct kinetics than the classical H 1 currents; and (e) it was z 20-fold more sensitive to Zn 2 1 and was blocked by the histidine-reactive agent, diethylpyrocarbonate (DEPC). In summary, our results demonstrate that the NADPH oxidase or a closely associated protein provides a novel type of H 1 conductance during phagocyte activation. The unique properties of this conductance suggest that its physiological function is not restricted to H 1 extrusion and repolarization, but might include depolarization, pH-dependent signal termination, and determination of the phagosomal pH set point.