Dining on the dead in the deep: Active <scp>NH<sub>4</sub><sup>+</sup></scp> excretion via <scp>Na<sup>+</sup>/H<sup>+</sup>(NH<sub>4</sub><sup>+</sup>)</scp> exchange in the highly ammonia tolerant Pacific hagfish, <i>Eptatretus stoutii</i>
Bibliographic record
Abstract
Abstract Aim Pacific hagfish are exceptionally tolerant to high environmental ammonia (HEA). Here, we elucidated a cellular mechanism that enables hagfish to actively excrete ammonia against steep ammonia gradients expected to be found inside a decomposing whale carcass. Methods Hagfish were exposed to varying concentrations of HEA in the presence or absence of environmental Na+, while plasma ammonia levels were tracked. 14C‐methylammonium was used as a proxy for NH4+ to measure efflux in whole animals and in isolated gill pouches; the latter allowed us to assess the effects of amiloride specifically on Na+/H+ exchangers (NHEs) in gill cells. Western blotting and immunohistochemistry were utilized to evaluate the abundance and sub‐cellular localization of Rhesus glycoprotein (Rh) channels in the response to HEA. Results Hagfish actively excreted NH4+ against steep inwardly directed ENH4+ (ΔENH4+ ~ 35 mV) and pNH3 (ΔpNH3 ~ 2000 μtorr) gradients. Active NH4+ excretion and plasma ammonia hypo‐regulation were contingent on the presence of environmental Na+, indicating a Na+/NH4+ exchange mechanism. Active NH4+ excretion across isolated gill pouches was amiloride‐sensitive. Exposure to HEA resulted in decreased abundance of Rh channels in the apical membrane of gill ionocytes. Conclusions During HEA exposure, hagfish can actively excrete ammonia against a steep concentration gradient using apical NHEs energized by Na+‐K+‐ATPase in gill ionocytes. Additionally, apical Rh channels are removed from the apical membrane, presumably to reduce ammonia loading from the environment. We suggest that this mechanism allows hagfish to maintain tolerable ammonia levels while feeding inside decomposing carrion, allowing them to exploit nutrient‐rich food‐falls.
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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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".