title: Characterization of a complement-fragment-C5a-stimulated calcium-influx mechanism in U937 monocytic cells.
abstract: The mechanism by which complement fragment C5a elevates intracellular Ca2+ ([Ca2+]i) levels in two cell types, a monocytic cell line, U937, and neutrophils, has been investigated by the use of fluorometric and radiometric techniques. In U937 cells the influx of extracellular Ca2+ can be distinguished from the release of intracellular Ca2+ stores in terms of dose-responsiveness to C5a and sensitivity to pertussis-toxin poisoning. This suggests that the mechanism of Ca2+ influx in these cells is at least partially independent of both the production of inositol phosphates and elevation of internal Ca2+ concentration. The C5a-stimulated influx of 45Ca2+ into U937 cells is inhibited by a series of metal ions (Zn2+ > Co2+ > Mn2+ > Sr2+ approximately equal to Ni2+ > La3+). The stimulated influx of Ca2+ into neutrophils is inhibited differently (Ni2 >> Co2+ > Zn2+ approximately equal to La3+ > Mn2+ approximately equal to Sr2+), is less sensitive to C5a and both the influx of extracellular Ca2+ and the release of intracellular stores are equally sensitive to pertussis toxin treatment. Taken together these results indicate that [Ca2+]i is controlled in U937 monocytes by mechanisms distinct from those which appear to operate in other myeloid cells, such as neutrophils, stimulated with C5a and formylpeptide.
authors.affiliation: Krebs Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, U.K.
authors.forename: P N
authors.initials: PN
authors.lastname: Monk
authors.forename: L J
authors.initials: LJ
authors.lastname: Partridge
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002122:Calcium Chloride / Q000494:pharmacology; D002132:Calcium Radioisotopes; D002460:Cell Line; D002712:Chlorides / Q000494:pharmacology; D015936:Complement C5a / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D005434:Flow Cytometry; D006801:Humans; D007811:Lanthanum / Q000494:pharmacology; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism; D009532:Nickel / Q000494:pharmacology; D037342:Pertussis Toxin; D013050:Spectrometry, Fluorescence; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D002132:Calcium Radioisotopes; D002712:Chlorides; D010566:Virulence Factors, Bordetella; D017967:Zinc Compounds; C028521:lanthanum chloride; D004533:Egtazic Acid; C022838:nickel chloride; D007811:Lanthanum; D009532:Nickel; D015936:Complement C5a; C016837:zinc chloride; D037342:Pertussis Toxin; D002122:Calcium Chloride; D002118:Calcium