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 (Con) A] generate O2.cntdot.-, 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 (.DELTA..psi.) was measured by distribution of the lipophilic cation [3H]triphenylmethyl phosphonium ion. The Nernst equation yielded a resting .DELTA..psi. of -26.7 mV. Beginning within 10 s after exposure to the antigen-antibody complex or to Con A, the cells responded with a rapid hyperpolarization .fwdarw. depolarization .fwdarw. slow hyperpolarization. Even when phagocytosis was inhibited by cytochalasin B, the triphasic response was obtained providing evidence for surface interaction. The hyperpolarization response anteceded O2.cntdot.- generation (continuous recording) by at least 20-30 s.) 02.cntdot.- generation in response to immune complexes was stimulated by Ca2+; .DELTA..psi. remained unchanged. Lack of Ca2+ in the medium did not inhibit the .DELTA..psi. response. Dissociation of membrane hyperpolarization from subsequent metabolic response (02.cntdot.- generation) was found in the presence of steroids (hydrocortisone, methylprednisolone), which inhibited 02.cntdot.- generation but did not inhibit the .DELTA..psi. response to antigen-antibody complex. Because 02.cntdot.- generation could be stimulated (Ca2+) or depressed (steroids) without affecting .DELTA..psi., .DELTA..psi. is apparently involved in primary triggering of phagocytic cells and metabolic stimulation is apparently a secondary consequence of ligand-receptor interactions.