Effect of β-adrenergic stimulation on the relationship between membrane potential, intracellular [Ca2+] and sarcoplasmic reticulum Ca2+ uptake in rainbow trout atrial myocytes
Bibliographic record
Abstract
Long depolarizations cause a steady tonic contraction and induce sarcoplasmic reticulum (SR) Ca(2+)-uptake in trout atrial myocytes. Simultaneous measurements of cytosolic [Ca2+] ([Ca2+]i) and whole membrane current showed an elevated [Ca2+]i throughout the depolarization. Rapid caffeine (Caf) applications at -80 mV before and after a long depolarization were used to determine SR Ca2+ loading and its dependency on membrane potential and [Ca2+]i during depolarization. Following a 10 s depolarization, the maximal SR Ca2+ load was 597 micromol l(-1) and loading was half-maximal at -12 mV. The beta-adrenergic agonist isoproterenol (ISO) did not affect the maximal SR Ca2+ loading but shifted the potential for half-maximal loading by -26 mV. Following a 3 s depolarization, the maximal SR Ca2+ uptake rate (Vmax) was 418 micromol l(-1) s(-1) in control conditions. ISO did not affect Vmax, but significantly lowered the average free Ca2+ transient during the depolarization and shifted the K(0.5) for the relationship between SR Ca2+ uptake and [Ca2+]i from 1.27 in control to 0.8 micromol l(-1) with ISO. Following repetitive 200 ms depolarizations, ISO increased the L-type Ca2+ current (ICa) amplitude by 91+/-29% and the peak Ca2+ transient by 41+/-10%, and decreased the half life of the Ca2+ transient from 151+/-12 to 111+/-6 ms. Using the relationship between [Ca2+]i and SR Ca2+ uptake to calculate the total SR Ca2+ uptake during a Ca2+ transient elicited by a 200 ms depolarization, a significant increase in the SR Ca2+ uptake from 37+/-6 micromol l(-1) in control to 68+/-4 micromol l(-1) with ISO was seen. When normalized to the total Ca2+ transport the contribution of the SR was not significantly different in the absence (35+/-6%) or presence of ISO (41+/-4%). Exposure of cells to ISO and low extracellular [Ca2+] increased ICa by 67+/-40% (N=5) but significantly reduced SR Ca2+ uptake at membrane potentials above -30 mV. Together, these results suggest that (i) ISO has a stimulatory effect on the SR Ca2+ pump that may contribute to the faster decay of the Ca2+ transient, and (ii) the relative contribution of the SR to the Ca2+ removal during relaxation is not altered by ISO in trout atrial myocytes.
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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".