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Journal of Experimental Biology 57,367-373 (1972)
Published by Company of Biologists 1972

Evidence for an Effect of Ouabain on the Branchial Sodium-Excreting Pump of Marine Teleosts: Interaction between the Inhibitor and External Na and K

R. MOTAIS ¹ and J. ISAIA ¹

¹ Laboratoire de Physiologie Cellulaire et Groupe de Biologic Marine du C.E.A.-Faculté des Sciences de l' Université de Nice 06, Nice, France

1. In all marine fish, both stenohaline and euryhaline, the net sodium excretion by the gill, compensating for intestinal absorption, is the result of a Na_int-K_ext exchange.

2. In a euryhaline fish, such as the eel, in which a sodium exchange diffusion (linkage of sodium influx and outflux) also occurs, the two kinds of exchange (Na-Na and Na-K) can be regarded as alternative modes of behaviour of the same transport system. In normal sea water both exchanges take place at the same time; in K-free sea water the system exchanges Na for Na exclusively and in Na-free solution containing K the system exchanges Na for K exclusively.

3. The transport system is located on the external membrane since it is inhibited by ouabain added in the external medium.

4. The Na-K process is ouabain-sensitive but K can antagonize the inhibitory action of the glycoside. The Na-Na process on the other hand is not ouabain-sensitive.