Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 98, Issue 20, Pages 11680-11685Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.201398798
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Synaptotagmin I is a synaptic vesicle-associated protein essential for synchronous neurotransmission. We investigated its impact on the intracellular Ca2+-dependence of large dense-core vesicle (LDCV) exocytosis by combining Ca2+-uncaging and membrane capacitance measurements in adrenal slices from mouse synapto-tagmin I null mutants. Synaptotagmin I-deficient chromaffin cells displayed prolonged exocytic delays and slow, yet Ca2+-dependent fusion rates, resulting in strongly reduced LDCV release in response to short depolarizations. Vesicle recruitment, the shape of individual amperometric events, and endocytosis appeared unaffected. These findings demonstrate that synaptotagmin I is required for rapid, highly Ca2+-sensitive LDCV exocytosis and indicate that it regulates the equilibrium between a slowly releasable and a readily releasable state of the fusion machinery. Alternatively, synaptotagmin I could function as calcium sensor for the readily releasable pool, leading to the destabilization of the pool in its absence.
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