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When looking at this paragraph in Midorikawa's work for a fluorescence review I was confused, specifically around a time constant of ~4s being compared to ~300 ms.

  1. It is not explicitly mentioned so I assume the 300 ms is a time constant correct?
  2. How is the conclusion drawn that it is the step after tethering, priming, by the discrepancies in time constant? I am not hoping any readers know why biologically it is this way but rather how I can understand a 13x larger time constant can lead to conclusions that it is not rate-limiting? (emphasis mine)

By comparing the time course of fusion events and tethering events, it was suggested that tethering of new vesicles could refill the empty release sites with a time constant of ∼4 s. This is also surprising since the replenishment of the readily releasable vesicles (RRVs) at the calyx of Held terminal was estimated to be ∼300 ms by the electrophysiological experiments (Neher and Sakaba, 2008; Hallermann and Silver, 2013). Given that a depolarization elicit fusions of only a small fraction of already-tethered vesicles in TIRFM imaging, the discrepancy suggests that the replenishment time course was determined by the step after the tethering, i.e. priming.

Reference Midorikawa, M. (2018) Real-time imaging of synaptic vesicle exocytosis by total internal reflection fluorescence (TIRF) microscopy. Neuroscience Research, Volume 136, (2018), pp. 1-5, ISSN 0168-0102, https://doi.org/10.1016/j.neures.2018.01.008. (https://www.sciencedirect.com/science/article/pii/S0168010217307551)

Thank you for the help!

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  • $\begingroup$ @Maurice I don't think you can talk for everyone on the site. Still, the question could be borderline off-topic... and somehow feels homeworky. Some links to provide context wouldn't hurt, not to mention title is pretty impressively unclear. $\endgroup$
    – Mithoron
    Commented Apr 25, 2023 at 21:43
  • $\begingroup$ I linked the paper. I am writing a review of this total internal reflectance fluorescence microscopy paper which falls squarely into chemical biology and I was confused by the wording around results involving a time constant. Hope that provides enough context $\endgroup$
    – hoggywoggy
    Commented Apr 25, 2023 at 22:44
  • $\begingroup$ (1) yes. (2) The extract suggest that they are in fact measuring different events as a way of explaining the discrepancy. Only you can know this as I'm not familiar with how good these techniques are. I presume time constant is the reciprocal of rate constant and not half-life. $\endgroup$
    – porphyrin
    Commented Apr 26, 2023 at 7:28

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