โ Scribed by Maren, Thomas H.
No coin nor oath required. For personal study only.
By means of the appropriate isotopes injected into the spiny dogfish, Squalus acanthias, the transfer of all major ions into cerebrospinal fluid (CSF), aqueous humor (A) and endolymph (E) was studied. In addition, the effect of raising pCO~2~ in seaโwater upon HCO concentration of these fluids was measured. In the several types of experiments, acetazolamide or methazolamide was used to inhibit completely carbonic anhydrase. The rates of fluid formation and ion transfer in CSF and A were fairly close, but those for E were far slower. The general pattern of ion transport in the three fluids were the same, Na^+^ (or Na^+^ + K^+^ in E) entry > Clโ entry, and the difference was HCO. The greater rate constants for HCO, increase in its entry rate by elevation of pCO~2~, and inhibition of its appearance by the sulfonamides, show that this is a special case of transport; the ion is formed in secretory cells from gaseous CO~2~ + OHโ. Secretory cells at sites of formation of all the fluids contain both carbonic anhydrase and Na^+^โK^+^โATPโase, which subserve HCO formation and Na^+^ (or K^+^) transport. Comparison of these results with studies in mammals show that the vertebrate pattern for secretion of these three fluids is well established in the elasmobranch.
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