Effects of blebbistatin and Ca<sup>2+</sup> concentration on force produced during stretch of skeletal muscle fibers
Bibliographic record
Abstract
When activated muscle fibers are stretched at low speeds [≤ 2 optimal length (L(o))/s], force increases in two phases, marked by a change in slope [critical force (P(c))] that happens at a critical sarcomere length extension (L(c)). Some studies attribute P(c) to the number of attached cross bridges before stretch, while others attribute it to cross bridges in a pre-power-stroke state. In this study, we reinvestigated the mechanisms of forces produced during stretch by altering either the number of cross bridges attached to actin or the cross-bridge state before stretch. Two sets of experiments were performed: 1) activated fibers were stretched by 3% L(o) at speeds of 1.0, 2.0, and 3.0 L(o)/s in different pCa(2+) (4.5, 5.0, 5.5, 6.0), or 2) activated fibers were stretched by 3% L(o) at 2 L(o)/s in pCa(2+) 4.5 containing either 5 μM blebbistatin(+/-) or its inactive isomer (+/+). All stretches started at a sarcomere length (SL) of 2.5 μm. When fibers were activated at a pCa(2+) of 4.5, P(c) was 2.47 ± 0.11 maximal force developed before stretch (P(o)) and decreased with lower concentrations of Ca(2+). L(c) was not Ca(2+) dependent; the pooled experiments provided a L(c) of 14.34 ± 0.34 nm/half-sarcomere (HS). P(c) and L(c) did not change with velocities of stretch. Fibers activated in blebbistatin(+/-) showed a higher P(c) (2.94 ± 0.17 P(o)) and L(c) (16.30 ± 0.38 nm/HS) than control fibers (P(c) 2.31 ± 0.08 P(o); L(c) 14.05 ± 0.63 nm/HS). The results suggest that forces produced during stretch are caused by both the number of cross bridges attached to actin and the cross bridges in a pre-power-stroke state. Such cross bridges are stretched by large amplitudes before detaching from actin and contribute significantly to the force developed during stretch.
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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) | 0.001 | 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) | 0.000 | 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".