Active Blood Acidification Greatly Enhances Oxygen Supply to the Teleost Retina
Bibliographic record
Abstract
Most ray‐finned fishes possess a unique system for retinal oxygen delivery, where intracellular acidification of red blood cells (RBCs) in the retinal capillaries induces oxygen offloading from pH‐sensitive hemoglobin. A countercurrent vascular network, the choroid rete mirabile , posterior to the retina augments this “oxygen‐secretory” mechanism and confers retinal PO 2 values that can exceed 1300 mmHg in some species. We hypothesized that the choroid rete mirabile exerts an active role in intracellular RBC acidification to facilitate retinal oxygen secretion. We show the presence and enzymatic activities of extracellular carbonic anhydrase (CA) and vacuolar‐type H + ‐ATPase (VHA) in the lumen of the choroid rete mirabile . These data are consistent with a pathway, where VHA secretes H + into the choroid rete mirabile lumen, which combines with HCO 3 – to form CO 2 (catalyzed by extracellular CA) that rapidly diffuses into the RBC facilitating hemoglobin oxygen offloading. Next, we validated the model in vivo by injecting an extracellular CA inhibitor (C18) into the dorsal aorta of anesthetized rainbow trout with a PO 2 electrode implanted into the retina. Here, the inhibition of extracellular CA resulted in a rapid reduction in retinal PO 2 from 517 to 226 mmHg within minutes. These data strongly support the proposed model for RBC acidification in the choroid rete mirabile . Further, i n vivo data show that this mechanism primarily augments oxygen diffusion to the inner retinal segments involved in signal‐processing and that the evolution of this pathway was tightly associated with the morphological expansion of this part of the retina. Together, these data suggest that the evolutionary origin of retinal oxygen secretion in the early history of the ray‐finned fishes was associated with a greatly enhanced capacity for visual processing, potentially permitting improved visual prey detection and the colonization of novel environments.
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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".