The role of transmembrane cationic gradients in immune complex stimulation of human polymorphonuclear leukocytes

The role of monovalent cationic gradients in human polymorphonuclear leukocyte (PMNL) stimulation was investigated by monitoring immune complex‐stimulated transmembrane depolarization and superoxide production, events which accompany—and have been used as indicators of—PMNL activation. Abolishing only the Na+ gradient by substitution of choline for extracellular Na+ did not affect the resting membrane potential but reduced the rate of stimulus‐induced transmembrane depolarization to 50% of control. In contrast, collapsing both Na+ and K+ gradients by suspension in K+ buffer (high K‐PRK) depolarized the cells and reduced the stimulus‐induced rate of depolarization to 11% of control. Pretreatment of cells suspended in Na+ buffers with 5‐(N,N‐dimethyl)amiloride hydrochloride (DMA) or with valinomycin reduced by one‐half the rate of immune complex induced membrane depolarization. Conversely, in the absence of either or of both Na+ or K+ gradients, or in the presence of valinomycin, immune complex elicited an enhanced rate of superoxide production. However, PMNL prepared via NH4CI (NH4CI‐PMNL) instead of H2O (H2O‐PMNL) lysis of residual red blood cells exhibited an absolute requirement for an intact Na+ gradient in cell stimulation. The present results thus demonstrate that: (1) both Na+ and K+ gradients participate equally in the membrane depolarization elicited by immune complex; (2) neither a Na+ or a K+ gradient is required for immune complex activation, or for activity of the respiratory burst; and (3) an artifactual requirement for an intact Na+ gradient occurs in neutrophils prepared by the NH4CI lysis technique.