Carbonic anhydrase isoenzymes CA I and CA II in the human eye

The distribution of carbonic anhydrase was studied in human donor eyes by the cobalt-phosphate histochemical method of Hansson and by immunofluorescence and immunoperoxidase techniques using antisera specific against the human cytoplasmic isoenzymes CA I and CA II. Corneal endothelium displayed specific immunological staining for CA I and CA II. Distinct enzyme activity was observed histochemically in the plasma membranes and cytoplasm of the endothelium. In the ciliary processes immunological evidence for the presence of CA II was found both in pigmented (PE) and in nonpigmented (NPE) epithelium. Activity was observed in the cytoplasm and basolateral membranes of NPE, but only in the basal membranes of PE. In the lens the plasma membranes of both the epithelium and fibers displayed intense activity, whereas cytoplasmic enzyme activity was seen only in the epithelium. There was no activity in the lens capsule. Immunofluorescence studies were difficult because of autofluorescence, but the immunoperoxidase technique indicated the presence of both CA I and CA II in the lens. In the central retina, Müller cells stained for CA II. Histochemically, enzyme activity was seen in the cytoplasm and at the plasma membranes. Activity was also observed in some but not all cones. Electron microscopy revealed this to be located in the cristae and plasma membranes adjacent to the pigment epithelium. Activity was also found in PE. Neurons and rods lacked both immunological staining and activity. Endothelial cells of capillaries in ciliary processes and in the choroid stained for CA I and exhibited histochemical activity, particularly those which faced neighboring epithelial cells containing the enzyme. The isoenzyme CA III, which is resistant to inhibition by sulfonamides, did not appear to be present in these ocular tissues, since the histochemical staining of enzyme activity was completely abolished by 10(-6) M acetazolamide.