title: Stimulus-response coupling in the human neutrophil. Transmembrane potential and the role of extracellular Na+.
abstract: Receptor-ligand interactions at the surface of the human neutrophil induce lysosomal enzyme release and the generation of O2.-, responses which are anteceded by changes in the membrane potential (delta psi) as measured by [3H]-triphenylmethylphosphonium ion distribution. Surface stimuli (immune complexes, concanavalin A) initiated a rapid (less than 10 s) hyperpolarization response by both normal and cytochalasin B-treated cells. Replacement of extracellular Na+ with either K+ or choline depressed O2.- generation and lysosomal enzyme release in neutrophils exposed to concanavalin A or immune complexes. Replacement of Na+ with K+ led to a substantial fall in resting membrane potential, whereas replacement of Na+ with choline did not. Thus, depression of O2.- generation and lysosomal enzyme release in Na+-free medium were specifically due to a lack of extracellular Na+ and not to depolarization of the membrane. Although it has been shown that extracellular Na+, and possibly an influx of Na+, is required for optimal neutrophil function, neither depolarization nor Na+ influx per se was sufficient to activate fully these cells, since the Na+ ionophore, monensin, was not an effective stimulus for beta-glucuronidase release or O2.- generation. The hyperpolarization response to neutrophils exposed to immune complexes and to concanavalin A was greatly diminished in both high [K+] and [choline] buffers. Thus, extracellular Na+ was required for an optimal membrane potential response to receptor-ligand interaction. Since O2.- generation and lysosomal enzyme release in response to the Ca2+ ionophore, A23187, were also reduced in the absence of extracellular Na+, it was concluded that extracellular Na+ was also required after induction of Ca2+ fluxes. Ouabain (1 mM) had no effect on O2.- generation, lysosomal enzyme release or the hyperpolarization response to immune complexes, indicating that the hyperpolarization observed on stimulation cannot be due to the action of the electrogenic pump, (Na+ + K+)-ATPase. The experiments indicate that extracellular Na+ is required (1) in the delta psi response triggered by receptor-ligand interaction, and (2) at a step(s) subsequent to Ca2+ fluxes and common to O2.- generation and lysosomal enzyme release.
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000936:Antigen-Antibody Complex; D001692:Biological Transport / Q000187:drug effects; D002414:Cations, Monovalent; D003208:Concanavalin A; D006801:Humans; D006867:Hydrolases / Q000378:metabolism; D008247:Lysosomes / Q000201:enzymology; D008564:Membrane Potentials / Q000187:drug effects; D008985:Monensin / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*; D013481:Superoxides / Q000097:blood
chemical_list: D000936:Antigen-Antibody Complex; D002414:Cations, Monovalent; D003208:Concanavalin A; D013481:Superoxides; D012710:Serum Albumin, Bovine; D000584:Amiloride; D008985:Monensin; D012964:Sodium; D006867:Hydrolases; D011188:Potassium