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Journal of Experimental Biology 70,213-220 (1977)
Published by Company of Biologists 1977

Further Evidence for Na/NH, Exchange in Marine Teleost Fish

DAVID H. EVANS ¹

¹ Department of Biology, University of Miami, Coral Gables, Florida, 33124, U.S.A.

1. Four species of marine teleosts were shown to possess an external-NH₄-inhibited Na uptake from 1 mM-NaCl solutions. The inhibition was not due to changes in the transepithelial potential.

2. Injection of 2 µM-NH₄/g fish stimulated Na uptake by Opsanus beta and also stimulated ammonia efflux, 50% of which was dependent upon external Na.

3. The ammonia efflux from three species was partially dependent upon external Na.

4. Na/NH₄ exchange in O. beta could be reversed so that ₂₂Na efflux could be stimulated by the addition of 200 mM-NH₄ to the external solution.

5. These studies show clearly that marine teleosts possess an Na/NH₄ exchange system in sea water which results in a net influx of Na into the fish.