title: Stimulus response coupling in the human neutrophil. Differential requirements for receptor occupancy in neutrophil responses to a chemoattractant.
abstract: Activated neutrophils aggregate, generate superoxide (O-2), and degranulate. The role of Ca as "second messenger" in neutrophil activation was examined using as agonist the chemotactic peptide fMet-Leu-Phe and its antagonist t-butoxycarbonyl-Phe-Leu-Phe-Leu-Phe to systematically vary the time of receptor occupancy. Release of enzymes from specific and azurophil granules showed a finite requirement for receptor occupancy; the cells were committed to full degranulation after 10 s of receptor-agonist interaction. In contrast, continuous occupation of the receptor by agonist was required to initiate and maintain O-2 generation and aggregation. Cytosolic Ca ( Quin2 fluorescence) increased immediately in response to fMet-Leu-Phe, requiring less than 2 s of agonist-receptor interaction to initiate an optimal response. Mobilization of membrane-associated Ca (chlorotetracycline fluorescence) also demonstrated a finite time requirement; the cells were fully committed after 10 s of agonist-receptor interaction. Increased Ca permeability (45Ca uptake) was fully launched after 15 s of agonist-receptor interaction. The data indicate that Ca movements ( quin2 , chlorotetracycline fluorescence, 45Ca uptake) are both necessary and sufficient to account for degranulation by neutrophils activated by fMet-Leu-Phe. However, neutrophil aggregation and the generation and release of O-2 in response to the same stimulus require a further unknown factor(s) associated with receptor occupancy to maintain these responses.
mesh_terms: D000328:Adult; D000409:Alanine / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000097:blood; D002449:Cell Aggregation / Q000187:drug effects; D002634:Chemotaxis, Leukocyte; D002751:Chlortetracycline / Q000494:pharmacology; D005456:Fluorescent Dyes; D006801:Humans; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects*; D010196:Pancreatic Elastase / Q000097:blood; D011956:Receptors, Cell Surface / Q000378:metabolism*; D044042:Receptors, Formyl Peptide; D013481:Superoxides / Q000097:blood; D013997:Time Factors
chemical_list: D005456:Fluorescent Dyes; D011956:Receptors, Cell Surface; D044042:Receptors, Formyl Peptide; D013481:Superoxides; C041828:N-tert-butyloxycarbonylalanine-4-nitrophenyl ester; D009240:N-Formylmethionine Leucyl-Phenylalanine; D010196:Pancreatic Elastase; D000409:Alanine; D002118:Calcium; D002751:Chlortetracycline