Location of calcium transporters at presynaptic terminals
Bibliographic record
Abstract
The plasma membrane ATP-driven Ca2+ pump (PMCA) and the Na+/Ca2+ exchanger (NCX) are the major means of Ca2+ extrusion at presynaptic nerve terminals, but little is know about the location of these transporters relative to the major sites of Ca2+ influx, the transmitter release sites. We used immunocytochemistry to identify these transport proteins in a calyx-type presynaptic nerve terminal from the ciliary ganglion of the chick. The PMCA clusters were localized to the transmitter release sites, as identified by staining for the secretory vesicle-specific protein synaptotagmin I. This colocalization was not due to the presence of the pump on the secretory vesicle itself because membrane fractionation of chick brain synaptosomes demonstrated comigration of the pump with surface membrane and not vesicle markers. In contrast, the NCX did not colocalize with synaptotagmin but tended to be located at nonsynaptic regions of the terminal. The PMCA location, near the transmitter release sites, suggests that it plays a role in priming the release site by maintaining a low free Ca2+ level, facilitating the dissociation of the ion from its binding sites. The PMCA may also replenish external Ca2+ in the synaptic cleft following periods of synaptic activity. In contrast, the NCX location suggests a role in the rapid emptying of cytoplasmic Ca2+ uptake organelles which serve as the main line of defence against high free Ca2+.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 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".