Haagsman H P, Schuurmans E A, Batenburg J J, van Golde L M
Laboratory of Veterinary Biochemistry, Utrecht University, The Netherlands.
Exp Lung Res. 1988;14(1):1-17. doi: 10.3109/01902148809062847.
Type II cells were exposed to ozone by gas diffusion through the thin Teflon bottom of culture dishes. The rate of phosphatidylcholine synthesis by type II cells, monitored by the incorporation of [Me-14C]choline, was impaired by ozone at concentrations that did not affect other cellular parameters. The enzymes choline kinase and cholinephosphate cytidylyltransferase were not susceptible to inactivation by ozone at concentrations at which the activity of glycerolphosphate acyltransferase was decreased. The enzyme activity of lactate dehydrogenase increased after ozone exposure. The specific activity of choline kinase in the cytosolic fraction of type II cells was fivefold that in whole lung. The metabolism of [Me-14C]choline was studied as a function of the choline concentration. Maximal rates of phosphatidylcholine synthesis were already attained at a concentration of 20 microM choline. Exposure of type II cells to ozone did not affect the recovery of label from [Me-14C]choline in choline phosphate and CDP choline. However, the maximal rate of phosphatidylcholine synthesis decreased after ozone exposure, which indicates that the decreased apparent activity of glycerolphosphate acyltransferase limits the supply of diacylglycerols and thereby the rate of phosphatidylcholine synthesis. If the flux through the diacylglycerol pathway was stimulated by the addition of palmitic acid, a higher maximal rate of phosphatidylcholine synthesis was observed. The uptake of [Me-14C]choline and the recovery of label in CDPcholine were not altered by the addition of different concentrations of palmitate. It is concluded that type II cells take up choline very efficiently, probably due to the high specific activity of choline kinase. At low choline concentrations the rate of phosphatidylcholine synthesis is determined by the supply of CDPcholine. At concentrations of choline in the upper physiological range, the rate of phosphatidylcholine synthesis is determined by the availability of diacylglycerols, which in turn is limited by the apparent activity of glycerolphosphate acyltransferase.
II型细胞通过气体扩散穿过培养皿的薄聚四氟乙烯底部而暴露于臭氧中。通过[甲基 - 14C]胆碱的掺入来监测的II型细胞中磷脂酰胆碱合成速率，在不影响其他细胞参数的浓度下受到臭氧的损害。胆碱激酶和胆碱磷酸胞苷转移酶在甘油磷酸酰基转移酶活性降低的浓度下对臭氧失活不敏感。臭氧暴露后乳酸脱氢酶的酶活性增加。II型细胞胞质部分中胆碱激酶的比活性是全肺中的五倍。研究了[甲基 - 14C]胆碱的代谢作为胆碱浓度的函数。在胆碱浓度为20微摩尔时已经达到磷脂酰胆碱合成的最大速率。II型细胞暴露于臭氧并不影响[甲基 - 14C]胆碱在磷酸胆碱和CDP胆碱中的标记回收。然而，臭氧暴露后磷脂酰胆碱合成的最大速率降低，这表明甘油磷酸酰基转移酶表观活性的降低限制了二酰基甘油的供应，从而限制了磷脂酰胆碱的合成速率。如果通过添加棕榈酸刺激通过二酰基甘油途径的通量，则观察到更高的磷脂酰胆碱合成最大速率。添加不同浓度的棕榈酸盐不会改变[甲基 - 14C]胆碱的摄取和CDP胆碱中标记的回收。结论是II型细胞非常有效地摄取胆碱，这可能是由于胆碱激酶的高比活性。在低胆碱浓度下，磷脂酰胆碱合成速率由CDP胆碱的供应决定。在生理范围内较高的胆碱浓度下，磷脂酰胆碱合成速率由二酰基甘油的可用性决定，而二酰基甘油的可用性又受到甘油磷酸酰基转移酶表观活性的限制。
