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Expression of carbonic anhydrase isozyme III in the ciliary processes and lens
1Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-9205, USA.
Purpose:
To determine whether carbonic anhydrase isozyme (CA) III is expressed in the ciliary processes and lens.
Methods:
Total RNA was isolated from rabbit ciliary epithelium and human ciliary processes and from the anterior lens of rabbit, cow, and human eyes. First-strand cDNA was synthesized, and the polymerase chain reaction (PCR) was performed using oligomer primers designed to amplify CA III sequences specifically. Selected PCR products were eluted from agarose gels, cloned, and sequenced. Northern blots were performed to confirm the presence of CA III in these tissues.
Results:
Polymerase chain reaction products of the predicted size were generated from rabbit ciliary epithelium and from rabbit, bovine, and human lens. The sequence of the PCR product from human lens was identical to the published sequence of the corresponding region of the human CA III gene. The sequence of the PCR products from rabbit ciliary epithelium and bovine lens showed 88% and 97% identity, respectively, with the corresponding sequences for human CA III, suggesting that the PCR products corresponded to the rabbit and bovine orthologs. Northern blots confirmed the presence of CA III mRNA in the rabbit ciliary epithelium and in rabbit and bovine lens.
Conclusions:
mRNA for CA III is present in the intraocular tissues of rabbits, cows, and humans. The previous detection of CA III protein in the bovine lens is confirmed, and it extended to the lenses of other species, including humans. The detection of mRNA for CA III in the ciliary epithelium is new and suggests that the ciliary epithelium contains not only isozymes II and IV but isoenzyme III as well. Although the function of CA III in the eye is unknown, it may play a role in fluid transport and homeostasis.