<unk>  are ion<unk>  that have the unique property of opening with depolarization, but in a strongly pH-sensitive manner. The result is that these<unk>  open only when the electrochemical gradient is outward, such that their opening will only allow<unk> s to leave cells. Their function thus appears to be acid extrusion from cells.
Another important function occurs in phagocytes (e.g. eosinophils, neutrophils, macrophages) during the respiratory burst. When bacteria or other microbes are engulfed by phagocytes, the enzyme NADPH oxidase assembles in the membrane and begins to produce reactive oxygen species (ROS) that help kill bacteria. NADPH oxidase is electrogenic, moving electrons across the membrane, and<unk><unk>  open to allow<unk>  flux to balance the electron movement electrically.
References:
1Cherny, V.V., V.S. Markin, and T.E. DeCoursey. 1995. The voltage-activated hydrogen ion conductance in rat alveolar epithelial cells is determined by the pH gradient. J. Gen. Physiol. 105:861-896.
2DeCoursey, T.E. 2003.<unk>  and other<unk>  transfer pathways. Physiol. Rev. 83:475-579.
3Babior, B.M. 1999. NADPH oxidase: an update. Blood. 93:1464-1476.
4Henderson, L.M., J.B. Chappell, and O.T.G. Jones. 1987. The superoxide-generating NADPH oxidase of human neutrophils is electrogenic and associated with an H+<unk>  Biochem. J. 246:325-329.
5Murphy, R., and T.E. DeCoursey. 2006. Charge compensation in phagocytes. Biochim. Biophys. Acta: Bioenergetics. 1757:996-1011.
Voltage-gated proton channels
Magnesium transporters
Light-gated ion channel
Cyclic nucleotide-gated ion channel
Chloride channel
Tandem pore domain potassium channel
Calcium channel
Voltage-gated ion channel