The Mechanism of Sodium and Chloride Uptake by the Gills of a Fresh-Water Fish, Carassius auratus

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Abstract
The addition of NH4+ions to the external medium results in an inhibition of the Na influx and net uptake in Carassius auratus, while intraperitoneal injection of ammonium produces the opposite effect. The simultaneous Cl- balance is not significantly affected by these treatments. The addition of HCO3 - ions to the external medium results in a reduction of the influx and net flux of Cl-while injection of HCO3 - produces the opposite effect. The simultaneous Na balance is not significantly altered. The effects of the external additions are reversible after elimination of the excess NH4 +or HCO3 - ions by rinsing. Inhibition of carbonic anhydrase in the gill by injection of acetazoleamide produces a simultaneous inhibition of both Na and Cl exchanges. These results confirm the hypothesis of an exchange of Na for NH4 +, and HCO3 - for Cl- across the gill. A tentative schematic representation of the ionic absorption mechanisms in the branchial cell of the fresh-water teleosts is given. Similarities with other biological membranes and especially with the renal tubule are pointed out.