Heterogeneous distribution of alkaline phosphatase and gamma-glutamyl transpeptidase in the mouse nephron

In the mouse nephron, ALP and gamma-GT were found to be heterogeneously distributed along the proximal tubule. For both enzymes, 4 large categories of tubules could be recognized on the basis of the enzymatic activity: intense; intermediate; weak; negative. The localization of ALP and gamma-GT was in opposite gradient along the proximal tubule and it apparently corresponded to the 3 sequential segments S1, S2, and S3. In fact, S1 could be identified with certainty because this first portion was often seen attached to the renal corpuscle. This segment displayed a very intense ALP activity (category 1), but a weak one for gamma-GT (category 3). Intermediate tubules for ALP and gamma-GT activities (category 2) seemingly were parts of S2. Those tubules where ALP activity was weak (category 3) while that of gamma-GT was intense (category 1) probably belonged to S3. As a result, it becomes possible to clearly distinguish the segments S1, S2, and S3, not only on a structural and biochemical basis but as well by the localization of brush border enzymes. Distal tubules showed no enzyme activity (category 4). In other respects, the presence of ALP and gamma-GT on the parietal layer of Bowman's capsule strongly suggests that these tall cylindrical cells are morphologically and enzymatically identical to those of the S1 segment, and that they might have similar functional roles.