Mitochondrial oxidative capacities: Does functional capacity match maximum physiological demand?
Bibliographic record
Abstract
The oxygen-dependent processes of ATP synthesis in mitochondria is same in all mammals and birds (endothermic animals). However, some endothermic species have higher maximum O2 consumption rate per unit mass (VO2 max/Mb) than others during aerobic exercise. It is unclear whether the mitochondria of these endothermic species achieving higher VO2 max/Mb have inherently higher biochemical capacities for respiration than mitochondria from other species. To understand the relation between functional capacities (biochemical capacity) and maximum physiological requirements, the respiration rates of flight muscle mitochondria of hovering C. anna (in vivo mVO2) and the maximum oxygen consumption rate of isolated mitochondria (in vitro mVO2) were compared. To measure whole body VO2max of C. anna, C. anna hovered in heliox (21% oxygen and 79% helium gas mixture). In vivo mVO2 of C. anna flight muscles calculated using whole body VO2max was 10.5 ml O2/min x ml on average. Since in vitro mVO2 values are substrate-dependent, in vitro mVO2 was measured using different combinations of substrates: ones that donate electrons to the electron transport chain via NADH and those that donate electrons via both NADH and FADH2 (Gnaiger, 2009). The NADH and FADH2 -linked substrate combination elicited the highest in vitro mVO2 which was 6.8 ml O2/min × ml on average. The in vitro mVO2 measurement methods used in this study brought a gap between in vivo and in vitro rates closer than the previous study (Suarez et al., 1990); however, biochemical capacity was still 17.3 % lower than the maximum physiological rate. C. anna flight muscle cytochrome aa3 content measured using spectrophotometric method was 83.88 n mol/g muscle. The electron flux through cytochrome aa3 calculated using cytochrome aa3 content and VO2 of C. anna hovering in heliox at 86.7 electrons/second. This electron flux rate is only slightly higher than the rate of rat heart, but cytochrome aa3 content per gram muscle is about 6 times higher in hummingbird flight muscle than the rat heart muscle. This indicates the level of cytochrome aa3 expression and the physiological requirements are matched to maximum requirements in both hummingbird pectoral and rat cardiac muscles.
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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 | 0.003 | 0.009 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.003 |
| Scholarly communication | 0.005 | 0.006 |
| Open science | 0.002 | 0.003 |
| Research integrity | 0.002 | 0.002 |
| Insufficient payload (model declined to judge) | 0.007 | 0.002 |
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".