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

Recently, it was demonstrated that liver injury and TNF-alpha 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 re sult of, at least in part, activation of a chloride channel in Kupffer cell s by glycine, which hyperpolarizes the cell membrane and blunts increases i n intracellular calcium concentrations ([Ca2+](i)) similar to its action in the neuron. It is well known that hepatotoxicity due to LPS has a neutroph il-mediated component and that activation of neutrophils is dependent on in creases in [Ca2+](i). Therefore, the purpose of this study was to determine if glycine affected agonist-induced increases in [Ca2+](i) in rat neutroph ils. The effect of glycine on increases in [Ca2+](i) elicited either by the bacterial-derived peptide formyl-methionine-leucine-phenylalanine (FMLP) o r LPS was studied in individual neutrophils using Fura-2 and fluorescence m icroscopy, Both FMLP and LPS caused dose-dependent increases in [Ca2+](i), which were maximal at 1 mu M FMLP and 100 mu g/ml LPS, respectively. LPS in creased 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 similar to 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 mu M), 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 determ ined. Glycine caused a dose-dependent increase in chloride uptake into neut rophils with an ED50 of similar to 0.4 mM, an effect also prevented by 1 mu M strychnine. Glycine also significantly reduced the production of superox ide anion from FMLP-stimulated neutrophils. Taken together, these data prov ide clear evidence that neutrophils contain a glycine-gated chloride channe l that can attenuate increases in [Ca2+](i) and diminish oxidant production by this important leukocyte.