Branchial Ionic Uptake and Acid-Base Regulation in the Rainbow Trout, Salmo Gairdneri

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Abstract
Amiloride (10−4 M) inhibited sodium uptake in rainbow trout by 78% and was associated with a pronounced acidosis and decreases in both plasma total CO2 (Tcoco2)* and [HCO3−]. 4-acetamido-4′-iso-thiocyanatostilbene-2,2′ disulphonic acid (SITS) (10−4M) in the bathing medium inhibited chloride uptake by 66% and following 6 h a significant decrease in plasma [H+] and significant increases in TCOCO2 and [HCO3−] were observed. Inhibition of chloride uptake (50%) with external sodium bicarbonate (12 mM) resulted in a more rapid and pronounced alkalosis than did SITS inhibition. Hypercapnic acidosis had no significant effect on the rates of branchial sodium and chloride uptake. Increasing the concentration of sodium in the bathing water resulted in a less pronounced acidosis and a more rapid pH recovery during hypercapnia. These results are discussed with reference to the gill as an acid-base regulating structure. These findings are consistent with a gill model previously presented by Haswell, Randall & Perry (1980).