Brush Border

Do you know how the proximal tubule brush border is related to the Nobel Prize in Chemistry? Normal proximal tubules have a prominent apical brush border which is highlighted by periodic acid Schiff (PAS) staining. One clue, in fact, to the presence of tubular injury is the loss of this brush border PAS positivity. The ultrastructural correlate of this brush border is the individual microvilli that extend into the tubular lumen from the apical surface of the cell (Fig 2). These microvilli greatly amplify the cell surface area in contact with the luminal ultrafiltrate, more than half of which is reabsorbed in the proximal tubule. A key microvillous protein that enables such high reabsorptive capacity is aquaporin I. This is one of the first known molecular water channels described in mammalian systems, and the 2003 Nobel Prize in Chemistry was awarded to its discoverer, Dr. Peter Agre (Fig 3).