Ammonia independent sodium uptake mediated by Na+ channels and NHEs in the freshwater ribbon leech <i>Nephelopsis obscura</i>
Bibliographic record
Abstract
Freshwater organisms actively take up ions from their environment to counter diffusive ion losses due to inhabiting hypo-osmotic environments. The mechanisms behind active Na+ uptake are quite well understood in freshwater teleosts, however, the mechanisms employed by invertebrates are not. Pharmacological and molecular approaches were used to investigate Na+ uptake mechanisms and their link to ammonia excretion in the ribbon leech Nephelopsis obscura. At the molecular level, we identified a Na+ channel and a Na+/H+-exchanger (NHE) in the skin of N. obscura, where the NHE was upregulated when acclimated to extremely low [Na+] (0.05 mmol l−1, pH 5) conditions. Additionally, we found that leeches in dilute freshwater environments use both, a vacuolar-type H+-ATPase (VHA) assisted uptake via a Na+ channel and a NHE based mechanisms for Na+ uptake. Immunolocalization of VHA and Na+/K+ ATPase indicated at least two cell types present within leech skin, VHA+ and VHA− cells, where the VHA+ cells are likely involved in Na+ uptake. NKA was present throughout the epithelium. We also found that increasing ammonia excretion by decreasing water pH, ammonia loading leeches or exposing leeches to high environmental ammonia does not affect Na+ uptake providing indications that an NHE-Rh metabolon is not present and that ammonia excretion and Na+ uptake are not coupled in N. obscura. To our knowledge, this is the first study showing the mechanisms of Na+ uptake and their links to ammonia excretion in a freshwater invertebrate, where results suggest an ammonia-independent Na+ uptake mechanism relying on both Na+ channels and NHEs.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".