Rice W R, Ross G F, Singleton F M, Dingle S, Whitsett J A
Pediatrics/Neonatology Division, University of Cincinnati College of Medicine, Ohio 45267.
J Appl Physiol (1985). 1987 Aug;63(2):692-8. doi: 10.1152/jappl.1987.63.2.692.
Secretion of [3H]phosphatidylcholine ([3H]PC) from isolated rat pulmonary type II epithelial cells was inhibited by the surfactant-associated protein of Mr = 35,000 (SAP-35) purified from canine lung surfactant. SAP-35 inhibited [3H]PC secretion in a dose-dependent manner and significantly inhibited basal, phorbol ester, beta-adrenergic, and P2-purinergic agonist-induced [3H]PC secretion. SAP-35 significantly inhibited [3H]PC secretion from 1 to 3 h after treatment. The IC50 for inhibition of [3H]PC secretion by canine SAP-35 was 1-5 X 10(-6) g/ml and was similar for inhibition of both basal and secretagogue-stimulated release. Heat denaturation of SAP-35, addition of monoclonal anti-SAP-35 antibody, reduction and alkylation of SAP-35, or association of SAP-35 with phospholipid vesicles reversed the inhibitory effect on secretagogue-induced secretion. Inhibitory effects of SAP-35 were observed 3 h after cells were washed with buffer that did not contain SAP-35. Although SAP-35 enhanced reassociation of surfactant phospholipid with isolated type II cells, its inhibitory effect on secretion of [3H]PC did not result from stimulation of reuptake of secreted [3H]PC by type II cells. The inhibition of phospholipid secretion by SAP-35 was also not due to inhibition of PC or disaturated PC synthesis by SAP-35. SAP-35, the major phospholipid-associated protein in pulmonary surfactant, is a potent inhibitor of surfactant secretion from type II cells in vitro and may play an important role in homeostasis of surfactant in the alveolar space.
从犬肺表面活性剂中纯化得到的分子量为35,000的表面活性剂相关蛋白（SAP - 35）可抑制离体大鼠肺II型上皮细胞分泌[3H]磷脂酰胆碱（[3H]PC）。SAP - 35以剂量依赖方式抑制[3H]PC分泌，并显著抑制基础分泌、佛波酯、β - 肾上腺素能和P2 - 嘌呤能激动剂诱导的[3H]PC分泌。处理后1至3小时，SAP - 35显著抑制[3H]PC分泌。犬SAP - 35抑制[3H]PC分泌的IC50为1 - 5×10(-6) g/ml，对基础分泌和促分泌剂刺激释放的抑制作用相似。SAP - 35的热变性、添加抗SAP - 35单克隆抗体、SAP - 35的还原和烷基化，或SAP - 35与磷脂囊泡的结合可逆转对促分泌剂诱导分泌的抑制作用。在用不含SAP - 35的缓冲液洗涤细胞3小时后，仍观察到SAP - 35的抑制作用。尽管SAP - 35增强了表面活性剂磷脂与分离的II型细胞的重新结合，但其对[3H]PC分泌的抑制作用并非源于刺激II型细胞对分泌的[3H]PC的再摄取。SAP - 35对磷脂分泌的抑制作用也不是由于其抑制PC或二饱和PC的合成。肺表面活性剂中的主要磷脂相关蛋白SAP - 35是体外II型细胞表面活性剂分泌的有效抑制剂，可能在肺泡腔表面活性剂的稳态中起重要作用。
