FUSION PORE CLOSURE DETERMINES SUBQUANTAL KISS-AND-RUN SEROTONIN RELEASE FROM FULLY LOADED DENSE-CORE VESICLES

Kiss-and-run exocytosis from dense-core vesicles in cultured Hirudo medicinalis Retzius neurons releases 58,344±20,759 serotonin molecules (64% of the quantum), yet frozen-pore estimates match full-quantum content.

• Why it matters: It remains unclear whether subquantal serotonin release during kiss-and-run reflects fewer vesicle molecules or instead results from fusion-pore closure dynamics.
• What they did: The authors analyzed amperometric recordings of extrasynaptic serotonin release, fitted biexponential current dynamics with Ohmic cylindrical/toroidal pore models, used hydrated flux packing to infer peak pore diameters (2.1–3.2 nm), and applied frozen pore extrapolation to estimate vesicular serotonin content.
• The result: Frozen pore extrapolation gave 102,650±10,989 molecules per vesicle (n=15), similar to full-fusion quantum, while serotonin flux decayed faster than frozen-pore flux (half-peak at 0.59 [0.23–0.95] of the time), indicating pore closure governs subquantal release.

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