The large-conductance Ca2+-activated K+ channel is essential for innate immunity

Abstract

Neutrophil leukocytes have a pivotal function in innate immunity. Dogma dictates that the lethal blow is delivered to microbes by reactive oxygen species (ROS) and halogens, products of the NADPH oxidase, whose impairment causes immunodeficiency. However, recent evidence indicates that the microbes might be killed by proteases, activated by the oxidase through the generation of a hypertonic, K+-rich and alkaline environment in the phagocytic vacuole. Here we show that K+ crosses the membrane through large-conductance Ca2+-activated K+ (BK(Ca)) channels. Specific inhibitors of these channels, iberiotoxin and paxilline, blocked oxidase-induced 86Rb+ fluxes and alkalinization of the phagocytic vacuole, whereas NS1619, a BK(Ca) channel opener, enhanced both. Characteristic outwardly rectifying K+ currents, reversibly inhibited by iberiotoxin, were demonstrated in neutrophils and eosinophils and the expression of the alpha-subunit of the BK channel was confirmed by western blotting. The channels were opened by the combination of membrane depolarization and elevated Ca2+ concentration, both consequences of oxidase activity. Remarkably, microbial killing and digestion were abolished when the BK(Ca) channel was blocked, revealing an essential and unexpected function for this K+ channel in the microbicidal process.

Anti-inflammatory effects of 8-hydroxydeoxyguanosine in LPS-induced microglia activation: suppression of STAT3-mediated intercellular adhesion molecule-1 expression

“…This released oh 8 Gua protects intermolecular DNA from oxidative stress, acting as antioxidant when it exists as a separate molecule (Kim et al, 2004). Antioxidant agents have antiinflammatory effects because ROS, produced during inflammatory action by phagocytic immune cells, cause the death of pathogens (Ahluwalia et al, 2004). In agreement with studies of ROS production, oh 8 dG abolishes LPS-elicited ROS production in a dose-dependent manner ( Figure 2B).…”

VSOP/Hv1 proton channels sustain calcium entry, neutrophil migration, and superoxide production by limiting cell depolarization and acidification

“…More recently, potassium ions were proposed to provide the compensating charge and, by increasing the ionic strength within the phagosome, to activate cationic proteases required for bacterial killing (Reeves et al, 2002). However, the claim that Ca 2+ -activated K + channels (BK Ca ) are required for bacterial killing by neutrophils (Ahluwalia et al, 2004) was disproved because neutrophils lack BK Ca currents and kill microbes efficiently in the presence of BK Ca inhibitors or after genetic ablation of the BK Ca channel (Femling et al, 2006;Essin et al, 2007Essin et al, , 2009). Modeling indicates that other potassium channels and swellingactivated chloride channels (Ahluwalia, 2008) contribute no more than 5% of the compensating charge, which is provided essentially by proton channels (Murphy and DeCoursey, 2006).…”

Inactivation of a bacterial virulence pheromone by phagocyte-derived oxidants: New role for the NADPH oxidase in host defense

“…Activation of the NADPH oxidase could contribute to host defense against S. aureus in many ways, from direct (20) and indirect (21) bacterial killing to regulating gene transcription of inf lammatory mediators (22). We hypothesized that phagocyte-derived oxidants act additionally as a barrier against density-dependent virulence by inactivating the pheromone autoinducers.…”