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

Abstract

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.