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

Abstract

Human granulocytes (polymorphonuclear leukocytes) exposed to surface stimuli [e.g., immune complexes, concanavalin A (Con A)] generate O(2).(-), 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 (DeltaPsi) was measured by distribution of the lipophilic cation [(3)H]triphenylmethyl phosphonium ion. The Nernst equation yielded a resting DeltaPsi 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 O(2).(-) generation (continuous recording) by at least 20-30 sec. O(2).(-) generation in response to immune complexes was stimulated by Ca(2+) whereas DeltaPsi remained unchanged; lack of Ca(2+) in the medium did not inhibit the DeltaPsi response. Dissociation of membrane hyperpolarization from subsequent metabolic responses (O(2).(-) generation) was also found in the presence of steroids (hydrocortisone, methylprednisolone), which inhibited O(2).(-) generation but did not inhibit the DeltaPsi response to antigen-antibody complex. Because O(2).(-) generation could be stimulated (Ca(2+)) or depressed (steroids) without affecting DeltaPsi, the data suggest that DeltaPsi is involved in primary triggering of phagocytic cells and that metabolic stimulation is a secondary consequence of ligand-receptor interactions.