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1 Laboratoire de Physiologie Respiratoire, Unité de Formation et de Recherche Cochin Port-Royal, Assistance Publique-Hôpitaux de Paris Université Paris V, and 2 Service de Médecine Néonatale, Hôpital Cochin Port-Royal, 75014 Paris, France; and 3 Laboratory of Veterinary Biochemistry and Graduate School of Animal Health, 3508 TD Utrecht, The Netherlands
The cellular mechanisms by which pulmonary surfactant exerts its effects, including anti-inflammatory or proinflammatory effects, have remained elusive. To address the issue of whether plasma membrane modifications represent a target for these mechanisms, we designed an experimental protocol involving the determination of changes in cAMP levels under membrane-dependent or -independent stimulatory pathways. The effects of a modified natural porcine surfactant, Curosurf, and the major surfactant protein A were evaluated on resting and stimulated cAMP levels of human monocytes. We found that agents that elevate intracellular cAMP exhibit different susceptibilities toward a preexposure to Curosurf. The rise in cAMP induced by membrane-active agents such as cholera toxin or the diterpene forskolin was significantly inhibited by monocyte preexposure to Curosurf. In contrast, the rise in cAMP induced by the membrane-permeant phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine or by the Bordetella pertussis toxin adenylate cyclase-hemolysin was unaffected by Curosurf. Surfactant protein A did not affect either cAMP levels or the inhibitory capacity of Curosurf. We suggest that a plasma membrane-associated event affecting the mechanism underlying the effects of cholera toxin or forskolin is involved in the inhibition of cAMP accumulation caused by Curosurf.
pulmonary surfactant; surfactant-associated protein A; adenosine 3',5'-cyclic monophosphate; plasma membrane
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