Intracellular LPS inhibits the activity of potassium channels and fails to activate NFkappaB in human macrophages.
Although much has been learned about signal transduction mechanisms and binding proteins involved in lipopolysaccharides (LPS)-induced activation of monocytes/macrophages, little is known about the ability of internalized LPS to activate cells. To approach this question we either exposed macrophages to LPS or microinjected the cells with LPS before studying early cellular events associated with LPS-mediated macrophage activation. We measured membrane currents and translocation of NFkappaB to the nucleus. Using the whole-cell patch clamp technique ion channels were analyzed and characterized as K+ sensitive inward and outward currents. Exogenous LPS was shown to increase the voltage-dependent outward current whereas the voltage-dependent inward current was unaffected. However when cells were microinjected with LPS both inward and outward current were completely abolished. The presence of LPS within the cells did not prevent them to perform phagocytosis or to respond to fMLP with an appropriate increase in [Ca2+]i. The immunocytological detection of NFkappaB p65 translocation revealed that exogenous LPS led to the nuclear localization of the p65 subunit of NFkappaB, whereas only the cytoplasmic localization of p65 was observed following microinjection of LPS. These data show that one major process in macrophage activation, the NFkappaB dependent transcription of a number of genes encoding for many inflammatory mediators cannot be induced by intracellular LPS but requires the interaction of LPS with external membrane components. However intracellular LPS causes a drastic decrease in potassium currents which by keeping the cell membrane at a depolarized potential may result in changed biological answers of these cells.
Gerth
Anja
A
Institute of Zoology, Department of Immunobiology, University of Leipzig, Liebigstrasse, Leipzig, Germany.
Grosche
Jens
J
Nieber
Karen
K
Hauschildt
Sunna
S
D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology; D008070:Lipopolysaccharides / Q000008:administration & dosage* / Q000494:pharmacology; D008264:Macrophages / Q000378:metabolism* / Q000502:physiology; D008845:Microinjections; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D016328:NF-kappa B / Q000378:metabolism*; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D010587:Phagocytosis; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D051996:Transcription Factor RelA; D015054:Zymosan / Q000378:metabolism
D007473:Ion Channels; D008070:Lipopolysaccharides; D016328:NF-kappa B; D015221:Potassium Channels; D051996:Transcription Factor RelA; D009240:N-Formylmethionine Leucyl-Phenylalanine; D015054:Zymosan; D002118:Calcium