Supramaximal cholecystokinin displaces Munc18c from the pancreatic acinar basal surface, redirecting apical exocytosis to the basal membrane

Stabilization of Exocytosis by Dynamic F-actin Coating of Zymogen Granules in Pancreatic Acini

“…In addition, retention of activated digestive enzymes in vacuoles may induce the digestion of the vacuolar membrane and facilitate its rupture. Third, physiological acinar polarity is disrupted by vacuole formation (14,44), which can result in granule fusion with the basolateral membrane (46,47) and in the formation of basolateral protrusions (13), eventually leading to autodigestion of the pancreas.…”

Alcohol/Cholecystokinin-evoked Pancreatic Acinar Basolateral Exocytosis Is Mediated by Protein Kinase Cα Phosphorylation of Munc18c

“…The preparation of isolated pancreatic acini from male Sprague-Dawley rats (125-150 g) was performed by a mechanical and enzymatic dissociation technique we previously described (1,16). The acini were resuspended in oxygenated Krebs-Ringer-HEPES (KRH) buffer, consisting of (in mM): 104 NaCl, 5 KCl, 1 KH 2 PO 4 , 1.2 MgCl 2 , 2 CaCl 2 , 0.2% (w/v) bovine serum albumin, 0.01% (w/v) soybean trypsin inhibitor, 10 glucose, 25 HEPES/ NaOH, pH 7.4, supplemented with minimal essential and nonessential amino acid solution and glutamine.…”

“…This well orchestrated exocytic pathway can be altered by supramaximal stimulation with cholecystokinin (CCK), which causes apical blockade and redirection of exocytosis to the basolateral plasma membrane (BPM) surface (1). Specifically, using epifluorescence imaging of the FM1-43 dye in pancreatic acinar cells, we showed real-time visualization of apical exocytosis induced by maximal CCK, and aberrant exocytosis at the BPM caused by supramaximal CCK stimulation (1).…”

“…This well orchestrated exocytic pathway can be altered by supramaximal stimulation with cholecystokinin (CCK), which causes apical blockade and redirection of exocytosis to the basolateral plasma membrane (BPM) surface (1). Specifically, using epifluorescence imaging of the FM1-43 dye in pancreatic acinar cells, we showed real-time visualization of apical exocytosis induced by maximal CCK, and aberrant exocytosis at the BPM caused by supramaximal CCK stimulation (1). We further found that this basolateral exocytosis was consistent with the paradigm of the SNARE Hypothesis (2)(3)(4)(5), involving a distinct set of cognate SNARE partners, Syntaxin-4 (Syn-4) and SNAP 23 on the BPM, and VAMP proteins on the ZG (1,6,7), and whose interactions were regulated by the SM protein Munc18c (1).…”

“…Specifically, using epifluorescence imaging of the FM1-43 dye in pancreatic acinar cells, we showed real-time visualization of apical exocytosis induced by maximal CCK, and aberrant exocytosis at the BPM caused by supramaximal CCK stimulation (1). We further found that this basolateral exocytosis was consistent with the paradigm of the SNARE Hypothesis (2)(3)(4)(5), involving a distinct set of cognate SNARE partners, Syntaxin-4 (Syn-4) and SNAP 23 on the BPM, and VAMP proteins on the ZG (1,6,7), and whose interactions were regulated by the SM protein Munc18c (1). Here, Munc18c on the acinar BPM binds Syn-4, and upon supramaximal CCK stimulation, becomes displaced into the cytosol via a PKC-mediated mechanism; which activates Syn-4 to become capable of forming a SNARE complex with its cognate partners, then proceeding to basolateral exocytosis (1).…”