Transmembrane potential changes associated with superoxide release from human granulocytes

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Abstract
Treatment of human granulocytes with concanavalin A, phorbol myristate acetate (PMA), N‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP), and A23187 (a calcium ionophore) stimulates the release of superoxide anion and the generation of chemiluminescence. The fluorescent probe, Di‐S‐C3(5), has been used to monitor shifts in membrane potential in response to these stimulants which precede the secretion of superoxide. Concanavalin A, PMA, and FMLP induce a biphasic shift in transmembrane potential (Em), i.e., a rapid depolarization followed by a prolonged hyperpolarization. This depolarization is dependent on both external sodium and calcium while the hyperpolarization is inhibited by ouabain which blocks the electrogenic Na‐K pump. In contrast, A23187 induces a rapid and prolonged depolarization. This monophasic shift in Em is dependent on external calcium. These results suggest that depolarization acts as a signal to initiate events associated with the “respiratory burst” of these phagocytes.