A novel K<sup>+</sup>‐dependent Na<sup>+</sup> uptake mechanism during low pH exposure in adult zebrafish (<i>Danio rerio</i>): New tricks for old dogma
Bibliographic record
Abstract
Abstract Aim To determine whether Na+ uptake in adult zebrafish (Danio rerio) exposed to acidic water adheres to traditional models reliant on Na+/H+ Exchangers (NHEs), Na+ channels and Na+/Cl− Cotransporters (NCCs) or if it occurs through a novel mechanism. Methods Zebrafish were exposed to control (pH 8.0) or acidic (pH 4.0) water for 0‐12 hours during which 22Na+ uptake (), ammonia excretion, net acidic equivalent flux and net K+ flux () were measured. The involvement of NHEs, Na+ channels, NCCs, K+‐channels and K+‐dependent Na+/Ca2+ exchangers (NCKXs) was evaluated by exposure to Cl−‐free or elevated [K+] water, or to pharmacological inhibitors. The presence of NCKXs in gill was examined using RT‐PCR. Results was strongly attenuated by acid exposure, but gradually recovered to control rates. The systematic elimination of each of the traditional models led us to consider K+ as a counter substrate for Na+ uptake during acid exposure. Indeed, elevated environmental [K+] inhibited during acid exposure in a concentration‐dependent manner, with near‐complete inhibition at 10 mM. Moreover, loss increased approximately fourfold at 8‐10 hours of acid exposure which correlated with recovered in 1:1 fashion, and both and were sensitive to tetraethylammonium (TEA) during acid exposure. Zebrafish gills expressed mRNA coding for six NCKX isoforms. Conclusions During acid exposure, zebrafish engage a novel Na+ uptake mechanism that utilizes the outwardly directed K+ gradient as a counter‐substrate for Na+ and is sensitive to TEA. NKCXs are promising candidates to mediate this K+‐dependent Na+ uptake, opening new research avenues about Na+ uptake in zebrafish and other acid‐tolerant aquatic species.
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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) | 0.001 | 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".