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pubmed:abstractText |
Studies were performed to elucidate further the phenomenon of secretagogue-mediated enhancement in the binding of the chemoattractant f-met-leu-[3H]phe to human neutrophils (PMN). Specific f-met-leu-[3H]phe binding to unstimulated PMN reached maximum levels after 10 to 15 min of incubation at 0 degrees C with a saturating concentration of peptide, and consisted of a readily displaceable and a nondisplaceable component. PMN, preexposed to A23187 (2.5 X 10(-8) M) or PMA (0.5 ng/ml) for 30 min at 37 degrees C to stimulate limited and preferential release of specific (secondary) granules (10 to 20% of total lysozyme, no beta-glucuronidase), demonstrated an approximate doubling in the displaceable component of f-met-leu-["3H]phe binding, accompanied by an increasing nondisplaceable component that could not be explained by bulk pinocytosis of extracellular fluid (assessed by [3H]sucrose uptake). The increase in f-met-leu-[3H]phe binding was not affected by inhibitors of protein synthesis, could not be attributed to the secreted products lysosyme or lactoferrin acting on the cell, and, on the basis of studies with PMN from patients with chronic granulomatous disease, could not be attributed to the effects of reactive oxygen species generated in low concentration during stimulation. Functional studies on PMN indicated that preexposure to secretagogues at concentrations demonstrated to increase receptor availability also enhanced subsequent f-met-leu-phe-mediated superoxide and hydrogen peroxide generation. The present data demonstrate that secretagogues may activate PMN to enhance their subsequent responses in f-met-leu-phe-mediated processes, and, combined with previous reports, support the concept that specific granules provide a source of preformed membrane and receptor material that is translocated to the cell surface during the secretion associated with directed locomotion.
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