Burczynski F J, Cai Z S, Moran J B, Forker E L
Department of Physiology, University of Missouri, Columbia 65212.
Am J Physiol. 1989 Oct;257(4 Pt 1):G584-93. doi: 10.1152/ajpgi.1989.257.4.G584.
We compared uptake of palmitate by hepatocyte monolayers with uptake by polyethylene membranes under conditions of identical binding and stirring. Hepatocytes and polyethylene display similar clearances when the fatty acid is free, reflecting partial rate limitation by diffusion across the unstirred water layer. When palmitate is 99.8% bound to albumin, however, hepatocytes clear free fatty acid about seven times faster than does polyethylene. We analyzed the uptake of palmitate by polyethylene at two different pHs to isolate the diffusive resistance of the unstirred layer and to show that codiffusion of bound and free palmitate to the hepatocyte surface accounts for only approximately 20% of the albumin-dependent increment in the clearance of free palmitate. The clearance data are supported by independent measurements of the stagnant layer thickness obtained from indicator dilution data and by an electrochemical method. The findings suggest that hepatocytes facilitate the dissociation of albumin-palmitate complexes. Alternatively, albumin may modulate the uptake capacities of hepatocytes and/or polyethylene.
我们在相同的结合和搅拌条件下，比较了肝细胞单层对棕榈酸的摄取与聚乙烯膜对棕榈酸的摄取。当脂肪酸处于游离状态时，肝细胞和聚乙烯表现出相似的清除率，这反映了跨未搅拌水层扩散造成的部分速率限制。然而，当棕榈酸与白蛋白的结合率达到99.8%时，肝细胞清除游离脂肪酸的速度比聚乙烯快约7倍。我们在两种不同的pH值下分析了聚乙烯对棕榈酸的摄取，以分离未搅拌层的扩散阻力，并表明结合态和游离态棕榈酸向肝细胞表面的共扩散仅占游离棕榈酸清除率中白蛋白依赖性增加量的约20%。清除率数据得到了从指示剂稀释数据和电化学方法获得的停滞层厚度独立测量结果的支持。这些发现表明，肝细胞促进了白蛋白 - 棕榈酸复合物的解离。或者，白蛋白可能调节肝细胞和/或聚乙烯的摄取能力。
