Ammonia excretion in the marine polychaeteEurythoe complanata(Annelida)

Abstract

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 NH 4 Cl (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.

Active mode of excretion across digestive tissues predates the origin of excretory organs

“…the Bilateria/Cnidaria split. Na + /K + ATPase, vacuolar H + ATPase and Rh/AMT have a remarkably conserved role in ammonia excretion mechanism within nephrozoans (24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36). In this study we show that the role of Na + /K + ATPase and likely of Rh and v-ATPase a, b in ammonia excretion extends beyond nephrozoans ( Fig.…”

“…We tested different inhibitor concentrations that were used in previous studies in other invertebrates (25,29,30,36,68). The concentrations of 5 µM Concanamycin C for inhibiting v-ATPase a/b, 1 mM Azetazolamide as an inhibitor of the carbonic anhydrase A 2, 1 mM Quabain to inhibit the Na + /K + ATPase and 2mM Colchicine for inhibiting the microtubule network were selected as the lowest that…”

“…genes expressed in the nephridia tubule and duct-associated cells composed of a) structural genes (rootletin) and b) solute carrier transporters (slc1 (glutamate/neutral amino acid transporters), slc4 (HCO3transporters), slc5 (Na + /Glucose transporters), slc8 (Na + /Ca2 + exchangers), slc9 (Na + /H + exchangers), slc12 (Na + /K + /2Clcotransporters), slc13 (Na + -sulfate(NaS)/carboxylate(NaC) cotransporters), slc26 (multifunctional anion transporters)) in vertebrates and planarians (21-23) as well as aquaporins (water/glycerol/ammonia transporters widely distributed on the phylogenetic tree with an osmoregulatory function (41)); 3.) genes involved in ammonia excretion in several nephrozoans (slc42/rhesus (ammonia transporters), Na + /K + ATPase, v-ATPase a, b and carbonic anhydrase A 2, 4) and expressed both in tubule and duct-associated cells of nephridia and in taxon-specific excretory organs or excretory structures (24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36).…”

“…We tested different inhibitor concentrations that were used in previous studies in other invertebrates (25,29,30,36,65…”

“…1B). Also, ammonia-secretion related genes encoding the Rhesus and Na + /K + ATPase transporters, the vacuolar H + -ATPase proton pump (a and b subunits) and the Carbonic Anhydrase A (2 and 4 members) are expressed in excretion sites of several nephrozoans, regardless whether they possess specialized excretory organs (24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35) or not (36,37) (Fig. 1C).…”