# Dynamics of membrane tension and synaptic vesicle recycling

> **NIH NIH R01** · YALE UNIVERSITY · 2022 · $421,144

## Abstract

Project Summary
Information in the nervous system is relayed mostly at synapses, where neurotransmitter is released with great
temporal precision from a presynaptic terminal via the fusion of membrane-bound synaptic vesicles (SVs) with
the plasma membrane (PM), in a process called exocytosis. Components of these SVs are subsequently
retrieved via endocytosis and recycled for reuse. This grant aims to understand the interplay between SV
recycling and membrane tension gradients and associated membrane flows.
In neurons and neuroendocrine cells, both exo- and endocytosis are influenced by osmotic forces, suggesting
they are influenced by membrane tension, 𝜎𝜎. Conversely, membrane addition to the PM via exocytosis is
expected to lower 𝜎𝜎, while endocytosis should restore it. In addition, 𝜎𝜎 has been suggested to be a possible
signal for coupling exo- to endocytosis. Despite these key roles, there are no measurements of 𝜎𝜎 in synaptic
terminals and how 𝜎𝜎 changes are related to exo-endocytosis is not known, mainly due to technical difficulties.
The best method to probe 𝜎𝜎 is to pull a thin membrane tether from the PM using optical tweezers; the tether
force reflects 𝜎𝜎. However, most terminals are small and tightly coupled to post-synaptic structures, making
tether pulling impractical. We overcome this challenge using fish bipolar neurons which possess giant
terminals, in a setup that combines optical tweezers with electrophysiology or photostimulation and with high-
resolution fluorescence microscopy. We aim to 1) characterize PM flows at neuronal presynaptic terminals.
After stimulation, membrane added at an exocytic site needs to flow (and the associated 𝜎𝜎 perturbation
propagate) over the cell surface, then through the tether to produce a change in the measured tether force. We
will characterize membrane flows. 2) Determine mechanisms of cell membrane flow regulation by the
cytoskeleton. We found that F-actin is a major regulator of PM-cytoskeleton drag, but how it interacts with the
PM at terminals and activity-dependent changes in its structure are not understood. We will characterize F-
actin rearrangements upon stimulation at the optical and electron microscopy levels. 3) Establish the
relationship between tension changes in response to stimulation, membrane flow, and exo-endocytosis
coupling. We will confirm that 𝜎𝜎 changes we observed in preliminary experiments are due to exo-endocytosis
and map the spatiotemporal relationship between exo- and endocyosis sites as a function of membrane flow to
test the idea that exo-endocytosis coupling may depend on membrane flow. 4) Do electromechanical effect
matter for exo- or endocytosis? We observed rapid voltage-induced tether force changes consistent with
electromechanical effects. The relevance of these effects to exo-endocytosis is not known. We will characterize
electromechanical effects and determine whether they may play a role during exo-endocytosis.
Overall, these measurements will help genera...

## Key facts

- **NIH application ID:** 10364698
- **Project number:** 5R01NS122388-02
- **Recipient organization:** YALE UNIVERSITY
- **Principal Investigator:** ERDEM KARATEKIN
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $421,144
- **Award type:** 5
- **Project period:** 2021-04-01 → 2026-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10364698

## Citation

> US National Institutes of Health, RePORTER application 10364698, Dynamics of membrane tension and synaptic vesicle recycling (5R01NS122388-02). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10364698. Licensed CC0.

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