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Originally published as MBC in Press, 10.1091/mbc.E09-03-0197 on May 6, 2009

Vol. 20, Issue 13, 3142-3154, July 1, 2009

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Cortical F-Actin, the Exocytic Mode, and Neuropeptide Release in Mouse Chromaffin Cells Is Regulated by Myristoylated Alanine-rich C-Kinase Substrate and Myosin II

Bryan W. Doreian, Tiberiu G. Fulop, Robert L. Meklemburg, and Corey B. Smith

Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106-4970

Submitted March 10, 2009; Revised April 16, 2009; Accepted April 29, 2009
Monitoring Editor: Adam Linstedt

Adrenal medullary chromaffin cells are innervated by the sympathetic splanchnic nerve and translate graded sympathetic firing into a differential hormonal exocytosis. Basal sympathetic firing elicits a transient kiss-and-run mode of exocytosis and modest catecholamine release, whereas elevated firing under the sympathetic stress response results in full granule collapse to release catecholamine and peptide transmitters into the circulation. Previous studies have shown that rearrangement of the cell actin cortex regulates the mode of exocytosis. An intact cortex favors kiss-and-run exocytosis, whereas disrupting the cortex favors the full granule collapse mode. Here, we investigate the specific roles of two actin-associated proteins, myosin II and myristoylated alanine-rich C-kinase substrate (MARCKS) in this process. Our data demonstrate that MARCKS phosphorylation under elevated cell firing is required for cortical actin disruption but is not sufficient to elicit peptide transmitter exocytosis. Our data also demonstrate that myosin II is phospho-activated under high stimulation conditions. Inhibiting myosin II activity prevented disruption of the actin cortex, full granule collapse, and peptide transmitter release. These results suggest that phosphorylation of both MARCKS and myosin II lead to disruption of the actin cortex. However, myosin II, but not MARCKS, is required for the activity-dependent exocytosis of the peptide transmitters.

This was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E09-03-0197) on May 6, 2009.

Address correspondence to: Corey B. Smith (corey.smith{at}case.edu)

Abbreviations used: APe, action potential equivalent; CgA/B, chromogranins A/B; MLCK, myosin light chain kinase; MPSD, myristoylated alanine-rich C-kinase substrate PKC substrate domain; RLC, regulatory light chain.




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