Electronmicroscopic Studies of Active Transport; Protein Reabsorption in Tubular Cells

　It is well known that proximal tubular cells reabsorb not only water, glucose and electrolytes, but also large molecular substances such as protein and lipoprotein．

　The mechanism of protein reabsorption in the proximal tubular cells has been described by many investigators as a process in which the protein included in the tubular fluid is reabsorbed into the cytoplasm by active movement of cell membrane（so called pinocytosis and athrocytosis）and then concentrated within the mitochondria or "droplets"．