Prolonged Low-frequency Force Depression Of Intact Single Mice Myofibers Is Partly Recovered With Post-Tetanic Potentiation
Bibliographic record
Abstract
PURPOSE: To assess whether prolonged low-frequency force depression (PLFFD) can be mitigated by post-tetanic potentiation (PTP) in intact single mice myofibers. METHODS: Intact single myofibers of the flexor digitorum brevis muscle of C57BL6 mice (~14 weeks old, n = 9) were dissected with tendons intact, microinjected with FURA-2 to measure intracellular calcium, perfused with Tyrode’s solution (21% O2 and 5% CO2 at 32 °C) and isometric force was recorded during electrical stimulations (350 ms trains, 8 V). To establish pre-fatigue values of force and calcium, myofibers were stimulated with 30, 50, 70 and 200 Hz contractions sequentially, separated by 2 s each (force-frequency protocol, FFP). To induce PLFFD, each myofiber was stimulated with 150 Hz contractions every 3 s until force dropped to 30% of initial. At 30-min following the fatiguing task, a FFP was applied before and immediately post six 150 Hz stimulations each separated by 2 s. The force before the six 150 Hz stimulations was used to assess PLFFD, and the force recorded after was used to assess the effect of PTP during the state of PLFFD. RESULTS: Myofibers (n = 9) required 70 ± 16 (mean ± SE) contractions to induce a 70% loss of force. At 30-min following fatigue, PLFFD was evident with force responses depressed at 30, 50, and 70 Hz and were ~ 40, ~33 and ~ 60% of pre-fatigue, respectively, (all P < 0.01) compared to 200 Hz which was ~85% of pre-fatigue (P < 0.05). Following six 150 Hz stimulations (i.e, PTP during PLFFD), force in response to 30, 50, and 70 Hz were ~ 195, ~260, and ~ 165% of PLFFD values, respectively, (all P ≤ 0.001) with no change in force at 200 Hz stimulation (~96% of pre-fatigue, P > 0.05). Therefore, inducing PTP during PLFFD enhanced single myofiber force closer to pre-fatigue values for the 30 (~80%), 50 (~87%) and 70 (~95%) Hz stimulations. CONCLUSIONS: In single myofibers from mice at near-physiological temperature, inducing PTP during PLFFD enhanced force in response to low and moderate frequencies. However, PLFFD could not be fully reversed by PTP. Therefore, despite impaired force generation during PLFFD single myofibers are sensitive to activation history force enhancement. Supported by NSERC. NSERC
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| 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) | 0.002 | 0.001 |
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".