Munc18/SNARE proteins' regulation of exocytosis in guinea pig duodenal Brunner's gland acini.
OBJECTIVE
To examine the molecular mechanism of exocytosis in the Brunner's gland acinar cell.


METHODS
We used a submucosal preparation of guinea pig duodenal Brunner's gland acini to visualize the dilation of the ductal lumen in response to cholinergic stimulus. We correlated this to electron microscopy to determine the extent of exocytosis of the mucin-filled vesicles. We then examined the behavior of SNARE and interacting Munc18 proteins by confocal microscopy.


RESULTS
One and 6 micromol/L carbachol evoked a dose-dependent dilation of Brunner's gland acini lumen, which correlated to the massive exocytosis of mucin. Munc18c and its cognate SNARE proteins Syntaxin-4 and SNAP-23 were localized to the apical plasma membrane, and upon cholinergic stimulation, Munc18c was displaced into the cytosol leaving Syntaxin-4 and SNAP-23 intact.


CONCLUSIONS
Physiologic cholinergic stimulation induces Munc18c displacement from the Brunner's gland acinar apical plasma membrane, which enables apical membrane Syntaxin-4 and SNAP-23 to form a SNARE complex with mucin-filled vesicle SNARE proteins to affect exocytosis.
Cosen-Binker
Laura-I
LI
Department of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
Morris
Gerry P
GP
Vanner
Stephen
S
Gaisano
Herbert Y
HY
D000818:Animals; D002011:Brunner Glands / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D018679:Cholinergic Agonists / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D004305:Dose-Response Relationship, Drug; D005089:Exocytosis / Q000187:drug effects; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D009077:Mucins / Q000378:metabolism*; D051938:Munc18 Proteins / Q000378:metabolism*; D050765:Qa-SNARE Proteins / Q000378:metabolism; D050600:SNARE Proteins / Q000378:metabolism*
D018679:Cholinergic Agonists; D009077:Mucins; D051938:Munc18 Proteins; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; D002217:Carbachol