Intracellular localization of carbonic anhydrase in the frog nephron.

The intracellular distribution of carbonic anhydrase has been studied in the frog nephron by a histochemical method. The study of the detailed intracellular localization was possible by sectioning tissue embedded in plastic (Sorwall, JB-4), before staining essentially according to Hansson. This procedure preserves the intracellular structure well and the resolution is high. For light microscopy sections from 1 to 10 mum were used. For electron microscopy 0.25 mum thick sections were stained and examined in the electron microscope using an accelerating voltage of 100 kV. The highest concentrations of the enzyme seem to be localized to the cell membranes or their immediate neighbourhood. A faint cytoplasmic staining may sometimes be observed. In distal tubule cells the apical part of the cell membrane was heavily stained. Weaker staining was found at the lateral membranes and their infoldings and to some extent the basal parts of the cell membrane. In the canaliculi cells only the lateral and basal parts of the membranes were stained. This latter localization is similar to that in the parietal cells of the mammalian stomach.