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 oxidase function. However, whether the NADPH oxidase—in analogy with mitochondrial cytochromes—has an inherent H⁺ channel activity remains uncertain: electrophysiological studies did not find altered H⁺ 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⁺ currents in human eosinophils. The “classical” H⁺ current had properties similar to previously described H⁺ conductances and was present in CGD cells. In contrast, the “novel” type of H⁺ current had not been described previously and displayed unique properties: (a) it was absent in cells from gp91- or 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⁺ currents; and (e) it was ∼20-fold more sensitive to Zn²⁺ 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⁺ conductance during phagocyte activation. The unique properties of this conductance suggest that its physiological function is not restricted to H⁺ extrusion and repolarization, but might include depolarization, pH-dependent signal termination, and determination of the phagosomal pH set point.