Ammonia is a toxic waste product from protein metabolism and needs to be either converted into less toxic molecules or, in the case of fish and aquatic invertebrates, excreted directly as is. In contrast to fish, very little is known regarding the ammonia excretion mechanism and the participating excretory organs in marine invertebrates. In the current study, ammonia excretion in the marine burrowing polychaete Eurythoe complanata was investigated. As a potential site for excretion, the 100–200 µm long, 30–50 µm wide and up to 25 µm thick dentrically branched, well ventilated and vascularized branchiae (gills) were identified. In comparison to the main body, the branchiae showed considerably higher mRNA expression levels of Na+/K+-ATPase, V-type H+-ATPase, cytoplasmic carbonic anhydrase (CA-2), a Rhesus-like protein, and three different ammonia transporters (AMTs). Experiments on the intact organism revealed that ammonia excretion did not occur via apical ammonia trapping, but was regulated by a basolateral localized V-type H+-ATPase, carbonic anhydrase and intracellular cAMP levels. Interestingly, the V-type H+-ATPase seems to play a role in ammonia retention. A 1 week exposure to 1 mmol l−1 NH4Cl (HEA) did not cause a change in ammonia excretion rates, while the three branchial expressed AMTs showed a tendency to be down-regulated. This indicates a shift of function in the branchial ammonia excretion processes under these conditions.
The authors declare no competing or financial interests.
D.T. performed qPCR experiments and provided together with M.H. the first draft of the MS; M.H. performed TEM imaging as well as light microscopy; H.M. performed western blotting and IHC experiments; A.R.Q.-R. conducted phylogentic analysis of the obtained sequences and produced gene tree; G.P. performed SEM experiments and supervised TEM imaging; A.P. provided funding; D.W. performed transport experiments and supervised the project; all authors revised and approved the draft.
This work was supported by the Incentive Award of the Faculty of Biology/Chemistry (University of Osnabrück) to H.M., and by grants from the Deutsche Forschungsgemeinschaft to A.P. and H.M. (SFB 944). A.P. received additional funding from the State of Lower-Saxony, Hannover, Germany [11-76,251-99-15/12 (ZN2832)]. A.R.Q.-R. and D.W. were funded by the Natural Sciences and Engineering Research Council of Canada.
Sequence information has been deposited in GenBank for: EcRhp1b (KX421088), EcAMT1 (KX458239), EcAMT3 (KX421089), EcAMT4 (KX421090), Eurythoe complanata carbonic anhydrase type 2 (KX421093), Eurythoe complanata V-type proton ATPase subunit B (KX421094), Eurythoe complanata glyceraldehyde 3-phosphate dehydrogenase (KX421092) and Eurythoe complanata Na/K-ATPase alpha-subunit (KX421091).
- Received July 4, 2016.
- Accepted November 11, 2016.
- © 2017. Published by The Company of Biologists Ltd