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 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) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 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) | 0.000 | 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".