Clapp W L, Park C H, Madsen K M, Tisher C C
Laboratory of Experimental Morphology, University of Florida College of Medicine, Gainesville.
Lab Invest. 1988 May;58(5):549-58.
Morphologic and physiologic studies have established that filtered proteins are absorbed in the proximal tubule by endocytosis and transported to the lysosomes for degradation. The tubular absorption, hydrolysis and accumulation of albumin were examined in all three segments of the rabbit proximal tubule. S1, S2 and S3 segments were dissected and perfused in vitro with tritiated albumin at a physiologic concentration of 0.0364 mg/ml, and with [14C]inulin to determine fluid reabsorption. In addition, the three segments were fixed for ultrastructural examination after perfusion under conditions similar to those in the physiologic studies. The fluid reabsorption was similar in S1 and S2 but lower in S3. Albumin absorption was unexpectedly similar in the three segments. A lower percentage of absorbed albumin was hydrolyzed in the S3 segment compared with the earlier segments. The values were 70 +/- 15%, 61 +/- 11%, and 30 +/- 4% for S1, S2, and S3, respectively. The cellular accumulation of protein was highest in the S3 segment. The ultrastructure of the three segments was similar to that described in in vivo preserved kidneys, and no abnormalities were observed in the endocytic-lysosomal compartment. These results reveal axial heterogeneity in the hydrolysis of absorbed albumin by the rabbit proximal tubule and suggest that under normal physiologic conditions the S3 segment has a lower lysosomal proteolytic activity. Although the S3 segment maintains a high capacity for protein absorption, the earlier proximal segments likely have a greater role in protein degradation.
形态学和生理学研究已证实，滤过的蛋白质在近端小管通过内吞作用被吸收，并转运至溶酶体进行降解。本研究检测了兔近端小管所有三个节段中白蛋白的肾小管吸收、水解及蓄积情况。分离出S1、S2和S3节段，在体外以生理浓度0.0364mg/ml的氚标记白蛋白及[14C]菊粉进行灌注，以测定液体重吸收。此外，在与生理学研究相似的条件下灌注后，将这三个节段固定以进行超微结构检查。S1和S2节段的液体重吸收相似，但S3节段较低。白蛋白吸收在这三个节段中出人意料地相似。与较早节段相比，S3节段中被水解的白蛋白百分比更低。S1、S2和S3节段的值分别为70±15%、61±11%和30±4%。蛋白质的细胞蓄积在S3节段最高。这三个节段的超微结构与体内保存肾脏中所描述的相似，在内吞溶酶体区室未观察到异常。这些结果揭示了兔近端小管对吸收的白蛋白水解存在轴向异质性，并表明在正常生理条件下，S3节段的溶酶体蛋白水解活性较低。尽管S3节段维持着较高的蛋白质吸收能力，但较早的近端节段可能在蛋白质降解中发挥更大作用。
