Involvement of membrane calcium in the response of rabbit neutrophils to chemotactic factors as evidenced by the fluorescence of chlorotetracycline.

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Abstract
Fluorescent chelate probe chlorotetracycline was used to investigate involvement of membrane Ca in rabbit peritoneal neutrophil response to chemotactic factors. Two chemotactic factors, the small MW fragment of the 5th component of complement C5a and the synthetic peptide formyl-methionyl-leucyl-phenylalanine (F-Met-Leu-Phe), were tested and found to decrease fluorescence of cell-associated chlorotetracycline in a manner strongly suggesting stimulus-induced displacement of membrane Ca. Time-course, concentration dependence and receptor specificity of Ca redistribution induced by the stimuli were consistent with its early role in initiation of various neutrophil functions. F-Met-Leu-Phe and C5a appeared to interact with the same pool of membrane Ca and released it to the cytoplasmic side of the plasma membrane. Intracellular Ca then bonds back to the membrane(s) from where it could be displaced by additional stimulation. Release of membrane Ca, experimentally defined here, appears to play a central role in initiation of various neutrophil functions.