Summary
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1.
Na and Cl efflux and gill potential were recorded simultaneously in sea water (SW)-adapted mullet.
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2.
After transfer of the fish to freshwater (FW), an instantaneous decline of the Na efflux was observed, explained by the reversal of the gill potential which occurred simultaneously.
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3.
Addition of increasing amounts of K or Na sulphate to FW was followed by a progressive depolarization or even a reversal of the gill potential and by a progressive increase of the Na efflux. K was far more efficient than Na in producing these effects.
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4.
The change in gill potential was not of sufficient magnitude to explain the observed increase of Na efflux.
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5.
Transfer from SW to FW also produced a decline of the Cl efflux. Addition of K to FW enhanced not only the Na but also the Cl efflux.
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6.
Injection of SCN was followed in SW-adapted fish by an increase in plasma Na and Cl and the Cl efflux was depressed by about 50% while the Na efflux remained unchanged.
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7.
After transfer of the fish to FW, the K dependent Na and Cl effluxes were depressed by SCN, while the depolarizing effect of K remained unchanged.
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8.
The SCN efflux across the gill represented only 0.1% of the Cl efflux. SCN does not substitute for Cl in the Cl extrusion pump.
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9.
These results suggest that the branchial Cl pump is associated with Cl exchange diffusion mechanism and with a Na/K exchange carrier insensitive to potential changes.
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Maetz, J., Pic, P. New evidence for a Na/K and Na/Na exchange carrier linked with the Cl− pump in the gill ofMugil capito in sea water. J Comp Physiol B 102, 85–100 (1975). https://doi.org/10.1007/BF00691295
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DOI: https://doi.org/10.1007/BF00691295