Abstract
The ionic composition of the aqueous humor and the rates of accession of the major ions to this fluid were studied in the spiny dogfish, Squalus acanthias. In terms of both sets of measurements, Na + and Cl − dominate greatly. Although there is carbonic anhydrase in the ciliary tissue, inhibition of the enzyme produces no effect upon turnover of any of the ions measured. This is due to very low normal concentrations of HCO 3 − CO 2 and the high degree of pCO 2 elevation caused by acetazolamide, which can drive the system past the enzymic block. In this fish, elevation of plasma pCO 2 is not reflected in the aqueous humor. In the cat, systemic hypercapnia does result in elevated pCO 2 in the aqueous. However, this does not lead to elevated aqueous HCO 3 −, in striking contrast to the effect in the cerebrospinal fluid (CSF). This experiment illustrates the difference between a system geared only to formation of HCO 3 − (aqueous) and those geared to HCO 3 − concentration as a means of pH regulation (CSF), or overall electrolyte homeostasis (kidney).
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