Surfactant modulates calcium response of neutrophils to physiologic stimulation via cell membrane depolarization.
Pulmonary surfactant (PS) reduces inflammation in the lung by poorly understood mechanisms. We have observed that surfactant-associated proteins (SAP) insert monovalent cation channels in artificial membranes. Neutrophils are primary mediators of acute pulmonary inflammation, and their functions are activated by increases in cytosolic ionized calcium concentration ([Ca2+]) and by changes in membrane potential. We hypothesize that PS inserts SAP-dependent cation channels in neutrophils, causing membrane depolarization, altered [Ca2+] response, and depressed activation. Human neutrophils were isolated, exposed to PS+SAP (1% Survanta), PS-SAP (1% Exosurf), or buffer, and washed before activating with selected stimulants. PS+SAP reduced phorbol ester- and formyl peptide-stimulated adherence and aggregation by 38% (p < 0.05) and 54% (p < 0.02), respectively. PS+SAP also inhibited the formyl peptide-induced [Ca2+] response of neutrophils (p < 0.01), but only in the presence of external Ca2+. Further characterization of this inhibition demonstrated that PS+SAP blocked formyl peptide-induced influx of both Ca2+ and Mn2+, and that this inhibition was present during activation by other neutrophil stimulants (IL-8, immune complexes). Prior depolarization of neutrophils with gramicidin-D similarly inhibited the [Ca2+] response of neutrophils to formyl peptide, and analysis of neutrophil membrane potential by 3,3'-dipentyloxaearbocyanine iodide (diOC5(3)) fluorescence revealed that PS+SAP induced rapid neutrophil depolarization. In contrast, PS-SAP exhibited little effect on neutrophil function, [Ca2+], or membrane potential. We conclude that PS+SAP decreases neutrophil adherence and aggregation responses, blocks Ca2+ influx after physiologic stimulation, and decreases membrane potential. We speculate that these effects are caused by membrane depolarization via SAP-dependent cation channel insertion, and that all of these effects contribute to the antiinflammatory properties of PS+SAP.
Chacon-Cruz
E
E
Center for Pediatric Research, Children's Hospital of The King's Daughters and Eastern Virginia Medical School, Norfolk, Virginia 23510-1001, USA.
Buescher
E S
ES
Oelberg
D G
DG
D000328:Adult; D002118:Calcium / Q000378:metabolism*; D002448:Cell Adhesion; D002449:Cell Aggregation; D005260:Female; D006096:Gramicidin / Q000494:pharmacology; D006801:Humans; D008297:Male; D008345:Manganese / Q000378:metabolism; D008564:Membrane Potentials; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D010743:Phospholipids / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011663:Pulmonary Surfactants / Q000494:pharmacology*
D010743:Phospholipids; D011663:Pulmonary Surfactants; D006096:Gramicidin; D008345:Manganese; D009240:N-Formylmethionine Leucyl-Phenylalanine; D011189:Potassium Chloride; D002118:Calcium