Rami J, Sasic S M, Rooney S A
Department of Pediatrics, Yale School of Medicine, New Haven, Connecticut 06510.
Am J Physiol. 1991 Jun;260(6 Pt 1):L577-85. doi: 10.1152/ajplung.1991.260.6.L577.
Silica instillation causes lung surfactant accumulation as well as hyperplasia and hypertrophy of type II pneumocytes. Two populations of type II cells can be isolated from silica-treated rats: type IIA, which are similar to type II cells from normal animals and type IIB, which are larger and have a higher rate of phosphatidylcholine biosynthesis. We have compared fatty acid biosynthesis and phosphatidylcholine secretion in types IIA and IIB cells and in type II cells from control rats. The cells were isolated by elastase digestion and panning on immunoglobulin G-coated plates and fractionated into types IIA and IIB by centrifugal elutriation. Type IIB cells contained more phospholipid and had an enhanced rate of [3H]choline incorporation into phosphatidylcholine. The activity of choline-phosphate cytidylyltransferase was elevated in the type IIB cells and the extent of the increase was diminished when phosphatidylglycerol was included in the assay, suggesting that the enhanced activity was due to enzyme activation rather than protein synthesis. The basal rate of phosphatidylcholine secretion was the same in all three groups as was the response to a variety of secretagogues. Incorporation of [3H]acetate into fatty acids was elevated in type IIB cells and the activity of fatty acid synthase was eightfold greater than in control cells. These data show that de novo fatty acid biosynthesis is increased in hypertrophic type II cells and that surfactant secretion is not elevated.
二氧化硅注入会导致肺表面活性物质积聚以及II型肺细胞增生和肥大。从经二氧化硅处理的大鼠中可分离出两类II型细胞：IIA型，与正常动物的II型细胞相似；IIB型，体积更大且磷脂酰胆碱生物合成速率更高。我们比较了IIA型和IIB型细胞以及对照大鼠II型细胞中的脂肪酸生物合成和磷脂酰胆碱分泌情况。通过弹性蛋白酶消化和在包被有免疫球蛋白G的平板上淘选分离细胞，并通过离心淘析将其分为IIA型和IIB型。IIB型细胞含有更多磷脂，且[3H]胆碱掺入磷脂酰胆碱的速率有所提高。胆碱磷酸胞苷转移酶的活性在IIB型细胞中升高，当检测中加入磷脂酰甘油时，升高程度减弱，这表明活性增强是由于酶的激活而非蛋白质合成。所有三组中磷脂酰胆碱的基础分泌速率相同，对各种促分泌剂的反应也相同。IIB型细胞中[3H]乙酸掺入脂肪酸的量增加，脂肪酸合酶的活性比对照细胞高八倍。这些数据表明，肥大的II型细胞中从头脂肪酸生物合成增加，而表面活性物质分泌并未升高。
