Chloride uptake in freshwater teleosts and its relationship to nitrite uptake and toxicity

Summary

• 1. The relationship between rate of chloride uptake and external chloride concentration was investigated in Rainbow trout,Salmo gairdneri, and Perch,Perca fluviatilis. The relationship between nitrite uptake and external nitrite and the inhibition of chloride uptake by nitrite was also investigated. Nitrite tolerance tests were performed on a variety of freshwater animals, including Carp,Cyprinus carpio, Tench,Tinca tinca, Pike,Esox lucius, Eel,Anguilla anguilla, and tadpoles,Rana temporaria.

• 2. The chloride uptake mechanism is saturable, with maximum uptake rates of 368 μMh⁻¹kg⁻¹ and 429 μMh⁻¹kg⁻¹ for the trout and perch, respectively. The half saturation value (K _m, the affinity constant) is 159 μMl⁻¹ for trout and 333 μMl⁻¹ for perch.

• 3. Net nitrite transport was determined in trout, net movement being into the fish against a concentration gradient, with a maximum uptake rate of 281 μMh⁻¹kg⁻¹; theK _m is 198 μMl⁻¹. This suggests that nitrite enters the fish via an active uptake process.

• 4. The data suggest that nitrite is a simple competitive inhibitor of active chloride uptake in both trout and perch. Trout are less tolerant of nitrite than perch (24-h LC₅₀ values are 0.7 mMl⁻¹ for trout and 1.2 mM l⁻¹ for perch) and also have a greater affinity for nitrite.

• 5. The spectrum of nitrite sensitivity seen in freshwater animals is discussed in relation to chloride uptake kinetics. These data support the hypothesis that nitrite uptake is an active process and furthermore uptake is linked quantitatively with chloride uptake, suggesting that chloride and nitrite enter the fish via the same route.