Characterization of Ca <sup>2+</sup> ‐Based Action Potentials in Horizontal Cells in the Goldfish ( <i>Carassius auratus</i> ) Retina
Bibliographic record
Abstract
About 65 years ago, the first intracellular recordings ever to be made in the retina were made in horizontal cells (HCs) of goldfish ( Carassius auratus ). These recordings were some of the first examples of graded potentials (where membrane potential changes in proportion with a stimulus), and it was assumed that outer retinal neurons did not present action potentials (APs). HCs are interneurons which provide inhibitory feedback to photoreceptors, and in vision they are responsible for improving contrast, edge detection, and color opponency. Since these first recordings, Ca 2+ ‐based APs and spontaneous increases in intracellular Ca 2+ concentration ([Ca 2+ ] i ) have been found in fish HCs, although they are poorly understood and their role in vision (if any) is unknown. We characterized spontaneous, Ca 2+ ‐based APs in isolated goldfish HCs by measuring changes in [Ca 2+ ] i and membrane potential ( V m ). Using Fura‐2 Ca 2+ imaging, we found spontaneous Ca 2+ activity characterized by transient elevation in [Ca 2+ ] i of short (seconds) and long (minutes) duration, in 157/177 cells (89%). These APs were similar in amplitude to Ca 2+ responses evoked by glutamate. APs were reversibly eliminated in Ca 2+ ‐free solutions (n=18), and were abolished by the L‐type Ca 2+ channel blocker, nifedipine (100 μM; n=5). APs were also dependent on intracellular Ca 2+ stores: they were abolished by the ryanodine receptor antagonists, ryanodine (20 μM; in 7/8 cells) and dantrolene (50 μM; n=7). The ryanodine receptor agonist, caffeine (n=10), increased AP frequency 2.8‐fold (p<0.0002) and reduced median duration (29.3 s to 18.7 s), time to peak (12.3 s to 7.8 s), and area under the curve (by 59.6%). When caffeine was co‐applied with the store‐operated channel antagonist, 2‐aminoethyldiphenyl borate (2‐APB), frequency was unaffected, further confirming a role for stores. We tracked changes in V m with whole‐cell current‐clamp recording, and with the voltage‐sensitive dye, FluoVolt. Phenotypes of APs in FluoVolt (n=6) and current‐clamp (48/57 cells; 84%) experiments displayed a sharp rise to peak, followed by a slow decline for the duration of the transient, and a steep return to baseline. In current‐clamp experiments, APs were dependent on L‐type Ca 2+ channel activity. APs were blocked by Co 2+ (5 mM; n=5) and nifedipine (100 μM; n=5), and were amplified and prolonged by the L‐type channel‐permeant ion, Ba 2+ (15 mM; n=6). In addition, APs were abolished in 6/9 cells in Ca 2+ ‐free solution. Collectively, our data suggest that activation of voltage‐dependent L‐type Ca 2+ channels leads to Ca 2+ influx, depolarization of V m , and additional Ca 2+ release from stores via ryanodine receptors. Understanding this phenomenon is a first step to elucidating a possible role for APs in vision or retinal physiology. This work also challenges the long‐held belief that outer retinal neurons do not present APs, and may lead to new paradigms about how visual information is encoded in the vertebrate retina. Support or Funding Information We acknowledge the support of the Natural Sciences and Engineering Research Council of Canada (NSERC), grant 342303. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.000 |
| 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 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".