Role of Ca2+ in changing active force during intermittent submaximal stimulation in intact, single mouse muscle fibers
Bibliographic record
Abstract
Fatigue of single mouse fibers during repeated high-frequency stimulation results initially from decreased Ca 2+ sensitivity while free myoplasmic calcium concentration ([Ca 2+ ] m ) increases, followed by decreasing [Ca 2+ ] m . Recovery of active force with low-frequency stimulation is slow and persistent fatigue results from low [Ca 2+ ] m . However, the consequences of intermittent submaximal contractions are not known. The aim of the present study was to investigate the changes in [Ca 2+ ] m and active force during intermittent submaximal contractions and subsequent recovery. Single fibers of mouse flexor digitorum brevis muscles at 32 °C were stimulated with 40 or 50 Hz, for 350 ms every 2 s for 2 min and then every 1 s until < 40% of initial force. Values obtained during the intermittent stimulation were compared with a control force-[Ca 2+ ] m relationship. A “P”-shaped pattern in the force-[Ca 2+ ] m relationship was observed during intermittent stimulation. Early in the intermittent stimulation, [Ca 2+ ] m increased while active force decreased. Subsequent force potentiation was accompanied by increased Ca 2+ sensitivity. Later, as active force declined, [Ca 2+ ] m decreased significantly ( p < 0.001). This was followed, in the final phase, by a significant decrease in Ca 2+ sensitivity determined by [Ca 2+ ] m at half-maximal force (Ca 50 ) ( p = 0.001). Low-frequency fatigue persisted during recovery while Ca 50 was not significantly different from prefatigue ( p > 0.5). In conclusion, the main mechanism of fatigue is due to decreases in both [Ca 2+ ] m and Ca 2+ sensitivity following the initial force potentiation. The intermittent submaximal contractions resulted in persistent low-frequency fatigue seen during recovery, which was explained by depressed [Ca 2+ ] m with no change in Ca 2+ sensitivity.
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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 | 0.001 | 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".