Expression of Nox1 in 3T3 cells increases cellular acid production but not proton conductance

Voltage-gated proton channels find their dream job managing the respiratory burst in phagocytes

The voltage-gated proton channel bears surprising resemblance to the voltage-sensing domain (S1-S4) of other voltage-gated ion channels but is a dimer with two conduction pathways. The proton channel seems designed for efficient proton extrusion from cells. In phagocytes, it facilitates the production of reactive oxygen species by NADPH oxidase.

Resveratrol inhibits foam cell formation via NADPH oxidase 1- mediated reactive oxygen species and monocyte chemotactic protein-1

Resveratrol is a polyphenolic compound in red wine that has anti-oxidant and cardioprotective effects in animal models. Reactive oxygen species (ROS) and monocyte chemotactic protein-1 (MCP-1) play key roles in foam cell formation and atherosclerosis. We studied LPS-mediated foam cell formation and the effect of resveratrol. Resveratrol pretreatment strongly suppressed LPS-induced foam cell formation. To determine if resveratrol affected the expression of genes that control ROS generation in macrophages, NADPH oxidase 1 (Nox1) was measured. Resveratrol treatment of macrophages inhibited LPS-induced Nox1 expression as well as ROS generation, and also suppressed LPS-induced MCP-1 mRNA and protein expression. We investigated the upstream targets of Nox1 and MCP-1 expression and found that Akt-forkhead transcription factors of the O class (FoxO3a) is an important signaling pathway that regulates both genes. These inhibitory effects of resveratrol on Nox1 expression and MCP-1 production may target to the Akt and FoxO3a signaling pathways.

Voltage-gated proton channels

The history of research on voltage-gated proton channels is recounted, from their proposed existence in dinoflagellates by Hastings in 1972 and their demonstration in snail neurons by Thomas and Meech in 1982 to the discovery in 2006 (after a decade of controversy) of genes that unequivocally code for proton channels. Voltage-gated proton channels are perfectly selective for protons, conduct deuterons half as well, and the conductance is strongly temperature dependent. These properties are consistent with a conduction mechanism involving hydrogen-bonded-chain transfer, in which the selectivity filter is a titratable amino acid residue. Channel opening is regulated stringently by pH such that only outward current is normally activated. Main functions of proton channels include acid extrusion from cells and charge compensation for the electrogenic activity of the phagocyte NADPH oxidase. Genetic approaches hold the promise of rapid progress in the near future.

Detailed comparison of expressed and native voltage-gated proton channel currents

Two years ago, genes coding for voltage-gated proton channels in humans, mice and Ciona intestinalis were discovered. Transfection of cDNA encoding the human HVCN1 (H(V)1) or mouse (mVSOP) ortholog of HVCN1 into mammalian cells results in currents that are extremely similar to native proton currents, with a subtle, but functionally important, difference. Expressed proton channels exhibit high H(+) selectivity, voltage-dependent gating, strong temperature sensitivity, inhibition by Zn(2+), and gating kinetics similar to native proton currents. Like native channels, expressed proton channels are regulated by pH, with the proton conductance-voltage (g(H)-V) relationship shifting toward more negative voltages when pH(o) is increased or pH(i) is decreased. However, in every (unstimulated) cell studied to date, endogenous proton channels open only positive to the Nernst potential for protons, E(H). Consequently, only outward H(+) currents exist in the steady state. In contrast, when the human or mouse proton channel genes are expressed in HEK-293 or COS-7 cells, sustained inward H(+) currents can be elicited, especially with an inward proton gradient (pH(o) < pH(i)). Inward current is the result of a negative shift in the absolute voltage dependence of gating. The voltage dependence at any given pH(o) and pH(i) is shifted by about -30 mV compared with native H(+) channels. Expressed H(V)1 voltage dependence was insensitive to interventions that promote phosphorylation or dephosphorylation of native phagocyte proton channels, suggesting distinct regulation of expressed channels. Finally, we present additional evidence that speaks against a number of possible mechanisms for the anomalous voltage dependence of expressed H(+) channels.