Neuron
Volume 28, Issue 2, November 2000, Pages 537-545
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Article
Dissection of Three Ca2+-Dependent Steps Leading to Secretion in Chromaffin Cells from Mouse Adrenal Slices

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Abstract

In neurosecretory cells, intracellular Ca2+ ([Ca2+]i) not only acts as the trigger for secretion but also regulates earlier steps in the secretory pathway. Here, a novel approach was developed to control [Ca2+]i over a broad concentration range, which allowed the quantification of three distinct actions of [Ca2+]i on large dense-core vesicle (LDCV) fusion in chromaffin cells from mouse adrenal slices. Basal [Ca2+]i regulated the transfer of vesicles toward a slowly releasable state, whereas further maturation to the readily releasable state was Ca2+ independent. [Ca2+]i levels above 3 μM triggered exocytosis of all readily and slowly releasable vesicles in two parallel, kinetically distinct fusion reactions. In a molecular context, these results suggest that Ca2+ acts both before and after trans-SNARE complex formation to regulate fusion competence and fusion kinetics of LDCVs.

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