Membrane-bound carbonic anhydrase activity in the rat corneal endothelium and retina

Localization of carbonic anhydrase (CA) was investigated in the rat eye by light and electron microscopy, and the inhibitory effects on CA distribution in the rat eye were compared between dorzolamide and acetazolamide. The cobalt sulfide histochemical method was used to study the CA localization. Acidic osmification was carried out for postfixation of the electron microscopic observations. The inhibition of CA activity was examined with different concentrations of acetazolamide and dorzolamide. The cytoplasm, lateral cell membranes and karyoplasm of the corneal endothelium showed CA activity. In the retina, the processes and cell bodies of Müller cells, the tips of the outer segments of the rods, and apical villi and basolateral membranes of the pigment epithelium indicated CA activity. CA activity was inhibited by dorzolamide at lower concentrations than needed for acetazolamide and only the CA activity of the nerve fiber layer remained at 10(-6) M of acetazolamide and 5 x 10(-7) M of dorzolamide. The presence of membrane-bound CA activity was confirmed in the corneal endothelium and Müller cells. CA activity was also demonstrated in the apices of rod outer segments and scleral fibroblasts. The CA inhibition test revealed that dorzolamide was a stronger CA inhibitor than acetazolamide and that the CA activity of the nerve fiber layer was strongest in the rat eye.