Chemotactic Factor-Induced Generation of Superoxide Radicals by Human Neutrophils: Evidence for the Role of Sodium

Open Access
Publisher Website
Google Scholar
Abstract
The role of sodium ion in superoxide (O-2) generation by human peripheral neutrophils was investigated. Cells were activated by exposure to the synthetic tripeptide, N-formyl-methionyl-leucyl-phenylalanine (FMLP), and O-2 release was assessed by ferricytochrome c reduction after 5 min of incubation at 37°C in the presence of FMLP 4 × 10-8 M. In the absence of monovalent cations (isotonic glucose), negligible O-2 generation occurred. There was a progressive increase in the magnitude of FMLP-induced O-2 generation with increasing Na+ concentration up to 90 mM, where the response was noted to plateau. Varying the K+ concentration (1 to 10 mM) had no effect on the amount of O-2 produced in the presence of Na+ 140 mM. FMLP also stimulated 22Na+ and 45Ca2+ uptake by the cells in a dose- and time-dependent fashion. FMLP-induced 22Na+ uptake appeared to be independent of the external Ca2+ concentration (0 to 4 mM). In contrast, there was a progressive decrease in the magnitude of the FMLP-induced increase in 45Ca2+ uptake as the Na+ concentration was reduced by replacement with choline+ or glucose. These studies support a requirement for Na+ in FMLP-induced O-2 generation and suggest that a Na+ influx may underlie the nature of this requirement. The data are also consistent with the hypothesis that a Na+ influx may precede the Ca2+ influx in the FMLP-induced activation sequence.