Proton currents in human granulocytes: regulation by membrane potential and intracellular pH.

1. To determine whether conductive pathways contribute to the H+ efflux from granulocytes, we used the whole‐cell patch‐clamp technique combined with microfluorimetric determinations of cytosolic pH (pHi) in single, dimethylsulphoxide‐differentiated HL‐60 cells. 2. In voltage‐clamp mode, depolarization of the cell from the resting potential (around ‐60 mV) to +60 mV caused an increase in pHi that was accompanied by a sizeable outward current. 3. Ion substitution experiments and analysis of the reversal potential of tail currents indicated that the outward current is carried largely by H+ ions. 4. Full activation of the H+ current occurred within 1‐2s after depolarization and deactivation within 100‐200 ms upon repolarization. 5. This H+ conductance was strongly dependent on pHi, being larger at acidic pH. In addition, at low pHi the threshold for voltage activation of the H+ conductance was shifted to more negative values. 6. Addition of millimolar concentrations of Cd2+ and Zn2+ to the bath solution reduced the maximum H+ conductance and shifted the voltage dependence of the H+ conductance to more positive potentials. The effects were reversible. 7. In conclusion, our results demonstrate that granulocytic HL‐60 cells possess a voltage‐gated and pHi‐sensitive H+ conductance. Because both a depolarization and a cytosolic acidification occur during the activation of granulocytes, this conductance may play a role in pHi homeostasis of granulocytes during microbial killing.