Glycine‐gated chloride channels in neutrophils attenuate calcium influx and superoxide production

Recently, it was demonstrated that liver injury and TNF-a production as a result of endotoxin (lipopolysaccharide, LPS) were attenuated by feeding animals a diet enriched with glycine. This phenomenon was shown to be a result of, at least in part, activation of a chloride channel in Kupffer cells by glycine, which hyperpolarizes the cell membrane and blunts increases in intracellular calcium concentrations ([Ca2+]i) similar to its action in the neuron. It is well known that hepatotoxicity due to LPS has a neutrophil-mediated component and that activation of neutrophils is dependent on increases in [Ca2+]i. Therefore, the purpose of this study was to determine if glycine affected agonist-induced increases in [Ca2+]i in rat neutrophils. The effect of glycine on increases in [Ca2+]i elicited either by the bacterial-derived peptide formyl-methi-onine-leucine-phenylalanine (FMLP) or LPS was studied in individual neutrophils using Fura-2 and fluorescence microscopy. Both FMLP and LPS caused dose-dependent increases in [Ca2+]i, which were maximal at 1 μM FMLP and 100 μg/ml LPS, respectively. LPS increased intracellular calcium in the presence and absence of extracellular calcium. Glycine blunted increases in [Ca2+]i in a dose-dependent manner with an IC50 of ~0.3 mM, values only slightly higher than plasma levels. Glycine was unable to prevent agonist-induced increases in [Ca2+]i in chloride-free buffer. Moreover, strychnine (1 μM), an antagonist of the glycine-gated chloride channel in the central nervous system, reversed the effects of glycine (1 mM) on FMLP- or LPS-stimulated increases in [Ca2+]i. To provide hard evidence for a glycine-gated chloride channel in the neutrophil, the effect of glycine on radioactive chloride uptake was determined. Glycine caused a dose-dependent increase in chloride uptake into neutro-phils with an ED50 of ~0.4 mM, an effect also prevented by 1 μM strychnine. Glycine also significantly reduced the production of superoxide anion from FMLP-stimulated neutrophils. Taken together, these data provide clear evidence that neutrophils contain a glycine-gated chloride channel that can attenuate increases in [Ca2+]i and diminish oxidant production by this important leukocyte.—Wheeler, M., Stachlewitz, R. F., Yamashina, S., Ikejima, K., Morrow, A. L., and Thurman, R. G. Glycine-gated chloride channels in neutrophils attenuate calcium influx and superoxide production. FASEB J. 14, 476–484 (2000)