Pulmonary surfactant-associated protein A enhances the surface activity of lipid extract surfactant and reverses inhibition by blood proteins in vitro.
Although a monolayer of dipalmitoylphosphatidylcholine, the major component of pulmonary surfactant, is thought to be responsible for the reduction of the surface tension at the air-liquid interface of the alveolus, the participation of unsaturated and anionic phospholipids and the three surfactant-associated proteins is suggested in the generation and maintenance of this surface-active monolayer. We have examined the effects of surfactant-associated protein A (SP-A) purified from bovine lavage material on the surface activity of lipid extract surfactant (LES), an organic extract of pulmonary surfactant containing all of the phospholipids and SP-B and SP-C, but lacking SP-A. Measurements of the surface tension during dynamic compression were made on a pulsating bubble surfactometer. Addition of SP-A to LES reduces the number of pulsations required to attain surface tensions near zero at minimum bubble radius. This increase in surface activity is dependent upon the presence of Ca2+ in the assay mixture. Maximal enhancement is observed at or below 1% of the lipid concentration (w/w). The addition of two blood proteins, fibrinogen and albumin, at physiological concentrations to LES causes severe inhibition of surface activity. Addition of SP-A in the presence of Ca2+ completely counteracts the inhibition by fibrinogen. The amount of SP-A required for full reversal of this inhibition was less than 0.5% of the lipid concentration. Complete reversal of inhibition by albumin was also observed, even though there was a approximately 5000-fold molar excess of inhibitor. Addition of lysophosphatidylcholine also inhibits LES; however, SP-A has no effect on this inhibition.
Cockshutt
A M
AM
Department of Biochemistry, University of Western Ontario, London, Canada.
Weitz
J
J
Possmayer
F
F
D015060:1,2-Dipalmitoylphosphatidylcholine; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D005340:Fibrinogen / Q000494:pharmacology*; D008244:Lysophosphatidylcholines / Q000494:pharmacology; D010743:Phospholipids / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011510:Proteolipids / Q000494:pharmacology* / Q000502:physiology; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology* / Q000502:physiology; D012709:Serum Albumin / Q000494:pharmacology*; D013500:Surface Tension / Q000187:drug effects*
D008244:Lysophosphatidylcholines; D010743:Phospholipids; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D012709:Serum Albumin; D015060:1,2-Dipalmitoylphosphatidylcholine; D005340:Fibrinogen; D002118:Calcium