Investigations on the role of Golgi-mediated, ligand-receptor processing in the activation of granulocytes by chemoattractants: differential effects of monensin |
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Authors: | R K Jesaitis C A Dahinden C M Chang A J Jesaitis |
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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. |
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