Summary
A series of experiments was conducted to investigate whether ammonia is excreted across the seawater-acclimated blue crab's gills as ionized NH +4 or as the free base, NH3. The net excretion rate of ammonia was not changed by transfer of the crabs to reduced (150 mM) Na+ solutions, by transfer to Na+- and K+-free artificial sea water, or by the sodium transport inhibitor amiloride. Ammonia excretion, therefore, does not appear to be linked to Na+ uptake in these animals, and appears to take place by passive diffusion. Since ammonia could diffuse either as NH +4 or NH3, we examined two other kinds of evidence. The trans-epithelial potential was measured in sea water and the various artificial media. In spite of a 10 mV more negative potential in Na+-, K+-free medium, the ammonia excretion was not reduced. Also, in alkalinized seawater in which the partial pressure gradient of NH3 was reduced, but the concentration gradient of NH +4 increased, ammonia excretion was reduced by about 70%. These results are consistent with the conclusion that ammonia excretion takes place by diffusion of the free base, NH3.
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Abbreviations
- SW :
-
sea water
- ASW :
-
artificial sea water
- t.e.p. :
-
transepithelial potential
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The University of Texas Marine Science Institute Contribution No. 461
Supported by NSF Grant PCM77-24358
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Kormanik, G.A., Cameron, J.N. Ammonia excretion in the seawater blue crab (Callinectes sapidus) occurs by diffusion, and not Na+/NH +4 exchange. J Comp Physiol B 141, 457–462 (1981). https://doi.org/10.1007/BF01101467
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DOI: https://doi.org/10.1007/BF01101467