[Roles of surfactant protein A (SP-A) and phospholipids on regulation of surfactant secretion from alveolar type II epithelial cells].
Surfactant protein A (SP-A) is known to inhibit surfactant secretion from pulmonary alveolar type II epithelial cells (type II cells). It is unknown whether SP-A acts as an inhibitor in the presence of lipids since SP-A mostly exists complexed with surfactant lipids. In this paper we focused on this issue using purified surfactant, purified SP-A and synthesized lipid liposomes. Surfactant secretion from type II cells was evaluated as TPA-stimulated secretion of radiolabeled lipids. The results demonstrated that 1) the inhibition of lipiD secretion by purified surfactant depended on its lipid components, not on the SP-A component, 2) the inhibitory effect of SP-A purified from surfactant was reversed in the presence of lipid liposomes, and 3) SP-A free from surfactant was unable to inhibit lipid secretion. We conclude from these results that SP-A can potentially inhibit surfactant secretion, but surfactant secretion is mainly regulated by surfactant lipids.
Suwabe
A
A
Department of Laboratory Medicine, Yamagata University School of Medicine.
Takahashi
K
K
D000818:Animals; D004847:Epithelial Cells; D066298:In Vitro Techniques; D010743:Phospholipids / Q000502:physiology*; D011510:Proteolipids / Q000502:physiology*; D011650:Pulmonary Alveoli / Q000166:cytology*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013501:Surface-Active Agents / Q000378:metabolism*
D010743:Phospholipids; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D013501:Surface-Active Agents