A highly Ca2+-sensitive pool of vesicles is regulated by protein kinase C in adrenal chromaffin cells
- Departments of ‡Biological Engineering,† Electrical Engineering, and §Physiology, and* Dalton Cardiovascular Research Center, University of Missouri, Research Park Drive, Columbia, MO 65211
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Communicated by Bertil Hille, University of Washington, Seattle, WA (received for review September 16, 2002)
Abstract
We have used flash photolysis of caged Ca2+ and membrane capacitance measurements to probe exocytosis in chromaffin cells at low concentrations of intracellular Ca2+ ([Ca2+]i) (<10 μM). We observed a small pool of granules that is more sensitive to [Ca2+]i than the previously described “readily releasable pool.” Upon activation of PKC, this “highly Ca2+-sensitive pool” is enhanced in size to a greater extent than the readily releasable pool but is eliminated upon expression of a C-terminal deletion mutant (Δ9) of synaptosome-associated protein of 25 kDa (SNAP-25). Thus, in chromaffin cells, PKC enhances exocytosis both by increasing the number of readily releasable vesicles and by shifting vesicles to a highly Ca2+-sensitive state, enabling exocytosis at sites relatively distant from Ca2+ channels.
Footnotes
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↵ ¶ To whom correspondence should be addressed. E-mail: gillisk{at}missouri.edu.
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See commentary on page 16522.
- Abbreviations:
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IRP, immediately releasable pool
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[Ca2+]i, intracellular Ca2+ concentration
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RRP, readily releasable pool
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HCSP, highly Ca2+-sensitive pool
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SNAP-25, synaptosome-associated protein of 25 kDa
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PMA, phorbol myristate acetate
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- Copyright © 2002, The National Academy of Sciences
