Lipopolysaccharide-sensitive H+ current in dendritic cells

Dendritic cells (DCs) are the most potent antigen-presenting cells equipped to transport antigens from the periphery to lymphoid tissues and to present them to T cells. Ligation of Toll-like receptor 4 (TLR4), expressed on the DC surface, by lipopolysaccharides (LPS), elements of the Gram-negative bacteria outer wall, induces DC maturation. Initial steps of maturation include stimulation of antigen endocytosis and enhanced reactive oxygen species (ROS) production with eventual downregulation of endocytic capacity in fully matured DCs. ROS production depends on NADPH oxidase (NOX2), the activity of which requires continuous pH and charge compensation. The present study demonstrates, for the first time, the functional expression of voltage-gated proton (Hv1) channels in mouse bone marrow-derived DCs. In whole cell patch-clamp experiments, we recorded Zn(2+) (50 μM)-sensitive outwardly rectifying currents activated upon depolarization, which were highly selective for H(+), with the reversal potential shift of 38 mV per pH unit. The threshold voltage of activation (V(threshold)) was dependent on the pH gradient and was close to the empirically predicted V(threshold) for the Hv1 currents. LPS (1 μg/ml) had bimodal effects on Hv1 channels: acute LPS treatment increased Hv1 channel activity, whereas 24 h of LPS incubation significantly inhibited Hv1 currents and decreased ROS production. Activation of H(+) currents by acute application of LPS was abolished by PKC inhibitor GFX (10 nM). According to electron current measurements, acute LPS application was associated with increased NOX2 activity.