Changes in membrane potential of human granulocytes antecede the metabolic responses to surface stimulation

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Human granulocytes (polymorphonuclear leukocytes) exposed to surface stimuli [e.g., immune complexes, concanavalin A (Con A)] generate O2·-, undergo a respiratory burst, and secrete lysosomal enzymes. To study the earliest reaction of ligands with surface receptors of granulocytes, purified cells were exposed to bovine serum albumin-anti-albumin complexes (Fc receptors) or Con A (glycoprotein receptors). The membrane potential (ΔΨ) was measured by distribution of the lipophilic cation [3H]triphenylmethyl phosphonium ion. The Nernst equation yielded a resting ΔΨ of -26.7 mV. Beginning within 10 sec after exposure to the antigen-antibody complex or to Con A, the cells responded with a rapid hyperpolarization → depolarization → slow hyperpolarization. Even when phagocytosis was inhibited by cytochalasin B, the triphasic response was obtained: evidence for surface interaction. The hyperpolarization response anteceded O2·- generation (continuous recording) by at least 20-30 sec. O2·- generation in response to immune complexes was stimulated by Ca2+ whereas ΔΨ remained unchanged; lack of Ca2+ in the medium did not inhibit the ΔΨ response. Dissociation of membrane hyperpolarization from subsequent metabolic responses (O2·- generation) was also found in the presence of steroids (hydrocortisone, methylprednisolone), which inhibited O2·- generation but did not inhibit the ΔΨ response to antigen-antibody complex. Because O2·- generation could be stimulated (Ca2+) or depressed (steroids) without affecting ΔΨ, the data suggest that ΔΨ is involved in primary triggering of phagocytic cells and that metabolic stimulation is a secondary consequence of ligand-receptor interactions.

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