Guthmann F, Haupt R, Looman A C, Spener F, Rüstow B
Abteilung Neonatologie, Charité, Humboldt-Universität zu Berlin, D-10098 Berlin, Germany.
Am J Physiol. 1999 Jul;277(1):L191-6. doi: 10.1152/ajplung.1999.277.1.L191.
Type II pneumocytes, which synthesize, store, and secrete pulmonary surfactant, require exogenous fatty acids, in particular palmitic acid, for maximum surfactant synthesis. The uptake of palmitate by type II pneumocytes is thought to be protein mediated, but the protein involved has not been characterized. Here we show by RT-PCR and Northern blot analysis that rat type II pneumocytes express the mRNA for fatty acid translocase (FAT/CD36), a membrane-associated protein that is known to facilitate the uptake of fatty acids into adipocytes. The deduced amino acid sequence from rat type II pneumocytes reveals 98% identity to the FAT/CD36 sequence obtained from rat adipocytes. The uptake of palmitate by type II pneumocytes follows Michaelis-Menten kinetics (Michaelis-Menten constant = 11.9 +/- 1.8 nM; maximum velocity = 62.7 +/- 5.8 pmol. min(-1). 5 x 10(5) pneumocytes(-1)) and decreases reversibly under conditions of ATP depletion to 35% of control uptake. Incubation of cells at 0 degrees C inhibited the uptake of palmitate almost completely, whereas depletion of potassium was without effect. Preincubation of the cells with bromobimane or phloretin decreases the uptake of palmitate significantly as does preincubation with sulfo-N-succinimidyl oleate, the specific inhibitor of FAT/CD36 (C. M. Harmon, P. Luce, A. H. Beth, and N. A. Abumrad. J. Membr. Biol. 121: 261-268, 1991). From these data, we conclude that FAT/CD36 is expressed in type II pneumocytes and mediates the uptake of palmitate in a saturable and energy-dependent manner. The data suggest that the uptake process is independent of the formation of coated pits and endocytotic vesicles.
II型肺泡上皮细胞合成、储存并分泌肺表面活性物质，其合成足量的表面活性物质需要外源性脂肪酸，尤其是棕榈酸。II型肺泡上皮细胞摄取棕榈酸的过程被认为是由蛋白质介导的，但相关蛋白质尚未得到鉴定。我们通过逆转录聚合酶链反应（RT-PCR）和Northern印迹分析表明，大鼠II型肺泡上皮细胞表达脂肪酸转位酶（FAT/CD36）的信使核糖核酸（mRNA），FAT/CD36是一种膜相关蛋白，已知其可促进脂肪酸进入脂肪细胞。从大鼠II型肺泡上皮细胞推导的氨基酸序列与从大鼠脂肪细胞获得的FAT/CD36序列有98%的同一性。II型肺泡上皮细胞摄取棕榈酸符合米氏动力学（米氏常数=11.9±1.8纳摩尔；最大速度=62.7±5.8皮摩尔·分钟-1·5×105个肺泡上皮细胞-1），在ATP耗竭的情况下，摄取量可逆性降低至对照摄取量的35%。细胞在0℃孵育几乎完全抑制了棕榈酸的摄取，而钾离子耗竭则无影响。用溴苯那敏或根皮素预孵育细胞可显著降低棕榈酸的摄取，用FAT/CD36的特异性抑制剂磺基-N-琥珀酰亚胺油酸酯预孵育也有同样效果（C.M.哈蒙、P.卢斯、A.H.贝思和N.A.阿布姆拉德。《膜生物学杂志》121:261-268，1991）。根据这些数据，我们得出结论，FAT/CD36在II型肺泡上皮细胞中表达，并以可饱和且能量依赖的方式介导棕榈酸的摄取。数据表明摄取过程独立于有被小窝和内吞小泡的形成。
