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- Adlimoghaddam 2015 J Exp Biol + (The soil-dwelling nematode ''Caenorhabditi โฆ The soil-dwelling nematode ''Caenorhabditis elegans'' is a bacteriovorous animal, excreting the vast majority of its nitrogenous waste as ammonia (25.3ยฑ1.2โ ยตmol gFW<sup>-1</sup> day<sup>-1</sup>) and very little urea (0.21ยฑ0.004โ ยตmol gFW<sup>-1</sup> day<sup>-1</sup>). Although these roundworms have been used for decades as genetic model systems, very little is known about their strategy to eliminate the toxic waste product ammonia from their bodies into the environment. The current study provides evidence that ammonia is at least partially excreted via the hypodermis. Starvation reduced the ammonia excretion rates by more than half, whereas mRNA expression levels of the Rhesus protein CeRhr-2, V-type H<sup>+</sup>-ATPase (subunit A) and Na<sup>+</sup>/K<sup>+</sup>-ATPase (ฮฑ-subunit) decreased correspondingly. Moreover, ammonia excretion rates were enhanced in media buffered to pH 5 and decreased at pH 9.5. Inhibitor experiments, combined with enzyme activity measurements and mRNA expression analyses, further suggested that the excretion mechanism involves the participation of the V-type H<sup>+</sup>-ATPase, carbonic anhydrase, Na<sup>+</sup>/K<sup>+</sup>-ATPase, and a functional microtubule network. These findings indicate that ammonia is excreted, not only by apical ammonia trapping, but also via vesicular transport and exocytosis. Exposure to 1โ mmol l<sup>-1</sup> NH4Cl caused a 10-fold increase in body ammonia and a tripling of ammonia excretion rates. Gene expression levels of CeRhr-1 and CeRhr-2, V-ATPase and Na<sup>+</sup>/K<sup>+</sup>-ATPase also increased significantly in response to 1โ mmol l<sup>-1</sup> NH4Cl. Importantly, a functional expression analysis showed, for the first time, ammonia transport capabilities for CeRhr-1 in a phylogenetically ancient invertebrate system, identifying these proteins as potential functional precursors to the vertebrate ammonia-transporting Rh-glycoproteins.monia transport capabilities for CeRhr-1 in a phylogenetically ancient invertebrate system, identifying these proteins as potential functional precursors to the vertebrate ammonia-transporting Rh-glycoproteins.)