Retinal carbonic anhydrase: a comparative study

Activity levels of carbonic anhydrase (E.C. 4.2.1.1) were measured in the retina and pigment epithelium of thirteen vertebrate species. The animals cover five taxonomic classes and among them illustrate four different retinal vascular supply patterns. The species can also be grouped according to their temperature regulatory mechanisms; i.e., homeothermic or poikilothermic. Significant differences are observed when the enzyme activities are examined by taxonomic class-birds and reptiles appear to have very high levels of enzyme activity; mammals and fish, moderate levels; and amphibia, low levels. When the enzyme activities are regrouped according to either vascular structure or temperature regulation, no significant differences are observed. From this, it is concluded that the level of carbonic anhydrase required by retinal tissue is not directly related to either of these factors. Carbonic anhydrase activity in kidney was compared with that in retina/pigment epithelium. Retina/pigment epithelium values are as great or greater than those in kidney but show a wider range. Only mammalian and avian kidney CA activity levels are high. We suggest that carbonic anhydrase levels in retina/pigment epithelium may be responsive to factors which influence vitreo-retinal ion and pH gradients.