The large-conductance Ca2+-activated K+ channel is essential for innate immunity.
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.
Ahluwalia
Jatinder
J
Department of Medicine University College London, Gower Street, London WC1E 6BT, UK.
Tinker
Andrew
A
Clapp
Lucie H
LH
Duchen
Michael R
MR
Abramov
Andrey Y
AY
Pope
Simon
S
Nobles
Muriel
M
Segal
Anthony W
AW
D002118:Calcium / Q000378:metabolism; D004553:Electric Conductivity; D004804:Eosinophils / Q000166:cytology / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007113:Immunity, Innate / Q000187:drug effects; D017136:Ion Transport / Q000187:drug effects; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials / Q000187:drug effects; D009504:Neutrophils / Q000166:cytology / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D010587:Phagocytosis / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012414:Rubidium Radioisotopes; D013211:Staphylococcus aureus / Q000276:immunology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism
D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D012414:Rubidium Radioisotopes; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium