Surfactant releases internal calcium stores in neutrophils by G protein-activated pathway.
Pulmonary surfactant with surfactant-associated proteins (PS+SAP) decreases pulmonary inflammation by suppressing neutrophil activation. We have observed that PS+SAP inserts channels into artificial membranes, depolarizes neutrophils, and depresses calcium influx and function in stimulated neutrophils. We hypothesize that PS+SAP suppresses neutrophil activation by depletion of internal Ca(++) stores and that PS+SAP induces depletion through release of Ca(++) stores and through inhibition of Ca(++) influx. Our model predicts that PS+SAP releases Ca(++) stores through insertion of channels, depolarization of neutrophils, and activation of a G protein-dependent pathway. If the model of channel insertion and membrane depolarization is accurate, then gramicidin-a channel protein with properties similar to those of PS+SAP-is expected to mimic these effects. Human neutrophils were monitored for [Ca(++)] responses after exposure to one of two different PS+SAP preparations, a PS-SAP preparation, gramicidin alone, and gramicidin reconstituted with phospholipid (PLG). [Ca(++)] responses were reexamined following preexposure to inhibitors of internal Ca(++) release or the G protein pathway. We observed that (i) 1% PS+SAP-but not PS-SAP-causes transient increase of neutrophil [Ca(++)] within seconds of exposure; (ii) 1% PLG-but not gramicidin alone-closely mimics the effect of PS+SAP on Ca(++) response; (iii) PS+SAP and PLG equally depolarize neutrophils; (iv) direct inhibition of internal Ca(++) stores releases or of G protein activation suppresses Ca(++) responses to PS+SAP and PLG; and (v) preexposure to either PS+SAP or PLG inhibits Ca(++) influx following fMLP stimulation. We conclude that PS+SAP independently depolarizes neutrophils, releases Ca(++) from internal stores by a G protein-mediated pathway, and alters subsequent neutrophil response to physiologic stimulants by depleting internal Ca(++) stores and by inhibiting Ca(++) influx during subsequent fMLP activation. The mimicking of these results by PLG supports the hypothesis that PS+SAP initiates depolarization via channel insertion into neutrophil plasma membrane.
Boston
Mark E
ME
Pediatric Otolaryngology Department, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229, USA.
Frech
G Christopher
GC
Chacon-Cruz
Enrique
E
Buescher
E Stephen
ES
Oelberg
David G
DG
D001896:Boron Compounds / Q000494:pharmacology; D002118:Calcium / Q000097:blood*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006096:Gramicidin / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D037342:Pertussis Toxin / Q000494:pharmacology; D010743:Phospholipids / Q000494:pharmacology; D011199:Potentiometry / Q000379:methods; D037661:Pulmonary Surfactant-Associated Proteins / Q000494:pharmacology; D011663:Pulmonary Surfactants / Q000494:pharmacology*
D001896:Boron Compounds; D007093:Imidazoles; D010743:Phospholipids; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D006096:Gramicidin; D009240:N-Formylmethionine Leucyl-Phenylalanine; C109986:2-aminoethoxydiphenyl borate; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium