Calcium release and intramembranous charge movement in frog skeletal muscle fibres with reduced (< 250 μM) calcium content
Bibliographic record
Abstract
It is generally accepted that activation of voltage sensors in the T-tubular membranes is a critical step of excitation-contraction coupling in skeletal muscle. The purpose of this study was to evaluate further whether the Qgamma component (delayed 'hump' component) of the intramembranous charge movement current (I(cm)) results from movement of these voltage sensors. Ca2+ release and I(cm) were measured in voltage-clamped frog cut fibres mounted in a double Vaseline-gap chamber. In order to reduce effects of Ca2+ feedback mechanisms, the calcium content of the sarcoplasmic reticulum (SR) during rest was reduced to < 250 microM (referred to volume of myoplasm) and maintained approximately constant. The early (Qbeta) and Qgamma components of charge movement were estimated by fitting the sum of two Boltzmann functions to the total steady-state intramembranous charge vs. voltage data. The average voltage steepness factor (k) and half-maximal voltage (V-) for Qgamma were 4.3 and -57.4 mV (n = 6), respectively. The SR membrane permeability for Ca2+ release was assessed when a constant amount of calcium remained in the SR (usually about 60 microM). A single Boltzmann function fitted to these data gave values on average for k and V- of 4.7 and -45.3 mV, respectively. The similarity of the values of k for Qgamma and Ca2+ release supports the idea that Qgamma reflects movement of voltage sensors for Ca2+ release. The greater value of V- for Ca2+ release compared to Qgamma is consistent with multi-state models of the voltage sensor involving movement of Qgamma charge during non-activating transitions.
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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 | 0.000 | 0.001 |
| 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".