Apamin-Sensitive Calcium-Activated Potassium Currents (SK) Are Activated by Persistent Calcium Currents in Rat Motoneurons
Bibliographic record
Abstract
Low voltage-activated persistent inward calcium currents (Ca PICs) occur in rat motoneurons and are mediated by Cav1.3 L-type calcium channels (L-Ca current). The objectives of this paper were to determine whether this L-Ca current activates a sustained calcium-activated potassium current (SK current) and examine how such SK currents change with spinal injury. For comparison, the SK current that produces the postspike afterhyperpolarization (mAHP) was also quantified. Intracellular recordings were made from motoneurons of adult acute and chronic spinal rats while the whole sacrocaudal spinal cord was maintained in vitro. Spikes/AHPs were evoked with current injection or ventral root stimulation. Application of the SK channel blocker apamin completely eliminated the mAHP, which was not significantly different in chronic and acute spinal rats. The Ca PICs were measured with slow voltage ramps (or steps) with TTX to block sodium currents. In chronic spinal rats, the PICs were activated at -58.6 +/- 6.0 mV and were 2.2 +/- 1.2 nA in amplitude, significantly larger than in acute spinal rats. Apamin significantly increased the PIC, indicating that there was an SK current activated by L-Ca currents (SK(L) current), which ultimately reduced the net PIC. This SK(L) current was not different in acute and chronic spinal rats. The SK(AHP) and the SK(L) currents were activated by different calcium currents because the mAHP/SK(AHP) was blocked by the N, P-type calcium channel blocker omega-conotoxin MVIIC and was resistant to the L-type calcium channel blocker nimodipine, whereas the L-Ca and SK(L) currents were blocked by nimodipine. Furthermore, the SK(AHP) current activated within 10 ms of the spike, whereas the SK(L) current was delayed approximately 100 ms after the onset of the L-Ca current, suggesting that the SK(L) currents were not as spatially close to the L-Ca currents. Finally, the SK(L) and the L-Ca currents were poorly space clamped, with oscillations at their onset and hysteresis in their activation and deactivation voltages, consistent with currents of dendritic origin. The impact of these dendritic currents was especially pronounced in 15% of motoneurons, where apamin led to uncontrollable L-Ca currents that could not be deactivated, even with large hyperpolarizations of the soma. Thus, although the SK(L) currents are fairly small, they play a critical role in terminating the dendritic L-Ca currents.
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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) | 0.000 | 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 | 0.000 |
| 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".