| Summary: | Remarkably little is known about nitrogenous excretion in freshwater invertebrates. In the current study, the nitrogen excretion mechanism in the carnivorous ribbon leech, Nephelopsis obscura, was investigated. Based on gene expression analysis and Ussing chamber experiments, the skin was identified as a major site of ammonia excretion. Pharmacological experiments and enzyme assays suggested an ammonia excretion mechanism that involves the V-ATPase, Na+/K+-ATPase and carbonic anhydrase, but not necessarily a functional microtubule system. Most importantly, functional expression studies of the identified Rh-protein cloned from leech skin (NoRhp) revealed an ammonia transport capability of this protein when expressed in yeast. Exposure to high environmental ammonia (HEA) caused a new adjustment of body ammonia, accompanied with a decrease in NoRhp and Na+/K+-ATPase mRNA levels, but unaltered ammonia excretion rates. The results of this study showed many similarities to the ammonia excretion mechanisms proposed in the gills of freshwater fish. === May 2015
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