Ammonia excretion via Rhcg1 facilitates Na<sup>+</sup>uptake in larval zebrafish, Danio rerio, in acidic water
Bibliographic record
Abstract
The involvement of a Na(+)/H(+) exchanger (NHE) in mediating Na(+) uptake by freshwater fish is currently debated. Although supported indirectly by empirical molecular and pharmacological data, theoretically its operation should be constrained thermodynamically, owing to unfavorable chemical gradients. Recently, there has been an increasing focus on ammonia channels (Rh proteins) as potentially contributing to Na(+) uptake across the freshwater fish gill. In this study, we tested the hypothesis that Rhcg1, a specific apical isoform of Rh protein, is critically important in facilitating Na(+) uptake in zebrafish larvae via its interaction with NHE. Treating larvae (4 days postfertilization) with 5-(N-ethyl-N-isopropyl) amiloride (EIPA), an inhibitor of NHE, caused a significant reduction in Na(+) uptake in fish reared in acidic water (pH ∼ 4.0). A role for NHE in Na(+) uptake was further confirmed by translational knockdown of NHE3b, an isoform of NHE thought to be responsible for Na(+)/H(+) exchange in zebrafish larvae. Exposing the larvae reared in acidic water to 5 mM external ammonium sulfate or increasing the buffering capacity of the water with 10 mM HEPES caused concurrent reductions in ammonia excretion and Na(+) uptake. Furthermore, translational knockdown of Rhcg1 significantly reduced ammonia excretion and Na(+) uptake in larvae chronically (4 days) or acutely (24 h) exposed to acidic water. Unlike in sham-injected larvae, EIPA did not affect Na(+) uptake in fish experiencing Rhcg1 knockdown. Additionally, exposure of larvae to bafilomycin A1 (an inhibitor of H(+)-ATPase) significantly reduced Na(+) uptake in fish reared in acidic water. These observations suggest the existence of multiple mechanisms of Na(+) uptake in larval zebrafish in acidic water: one in which Na(+) uptake via NHE3b is linked to ammonia excretion via Rhcg1, and another facilitated by H(+)-ATPase.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.004 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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 teacher head, 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".