title: Investigations on the role of Golgi-mediated, ligand-receptor processing in the activation of granulocytes by chemoattractants: differential effects of monensin.
abstract: Human granulocytes were exposed to different concentrations of the ionophore monensin for 20 min at 37 degrees C. Subsequent exposure to 50 nM of the chemoattractant fMet-Leu-[3H]Phe for up to 30 min at 37 degrees C resulted in a receptor-mediated uptake that was inhibited 80% at a monensin concentration of 30 microM. 50% inhibition was observed at 1-10 microM monensin with no significant change in fMet-Leu-Phe dose dependency. Subcellular fractionation of cells treated with monensin, indicated that the low density UDP-galactosyltransferase activity associated with internalized receptor-fMet-Leu-Phe complexes in untreated cells was absent. The high density galactosyltransferase activity cosedimenting with specific granule markers, however, was unaffected. Monensin also inhibited chemotaxis toward fMet-Leu-Phe as measured by migration of granulocytes through millipore filters and fMet-Leu-Phe induction of polarized morphology. Incubation of cell suspensions with up to 30 microM monensin, both before and during measurement of fMet-Leu-Phe stimulated superoxide production, did not affect the magnitude, kinetics, or transiency of the radical generation. Monensin did, however, shift the dose dependency of superoxide production of fMet-Leu-Phe to higher concentrations. These differential effects of monensin suggest that endocytosis of complexes of the chemoattractant and receptor is not involved in the activation or termination of the fMet-Leu-Phe stimulated superoxide production. They also are consistent with a role for receptor modulation and processing in the chemotactic response.
mesh_terms: D002634:Chemotaxis, Leukocyte / Q000187:drug effects*; D006056:Golgi Apparatus / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D006098:Granulocytes / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008854:Microscopy, Electron; D008985:Monensin / Q000494:pharmacology*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000097:blood / Q000494:pharmacology*; D013481:Superoxides / Q000097:blood
chemical_list: D013481:Superoxides; D009240:N-Formylmethionine Leucyl-Phenylalanine; D008985:Monensin