Supramaximal cholecystokinin displaces Munc18c from the pancreatic acinar basal surface, redirecting apical exocytosis to the basal membrane
Herbert Y. Gaisano, … , William S. Trimble, Anne Marie F. Salapatek
Herbert Y. Gaisano, … , William S. Trimble, Anne Marie F. Salapatek
Published December 1, 2001
Citation Information: J Clin Invest. 2001;108(11):1597-1611. https://doi.org/10.1172/JCI9110.
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Article

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

Abstract

Exocytosis at the apical surface of pancreatic acinar cells occurs in the presence of physiological concentrations of cholecystokinin (CCK) but is inhibited at high concentrations. Here we show that Munc18c is localized predominantly to the basal membranes of acinar cells. Supramaximal but not submaximal CCK stimulation caused Munc18c to dissociate from the plasma membrane, and this displacement was blocked by protein kinase C (PKC) inhibitors. Conversely, whereas the CCK analog CCK-OPE alone failed to displace Munc18c from the membrane, this agent caused Munc18c displacement following minimal PKC activation. To determine the physiological significance of this displacement, we used the fluorescent dye FM1-43 to visualize individual exocytosis events in real-time from rat acinar cells in culture. We showed that supramaximal CCK inhibition of secretion resulted from impaired apical secretion and a redirection of exocytic events to restricted basal membrane sites. In contrast, CCK-OPE evoked apical exocytosis and could only induce basolateral exocytosis following activation of PKC. Infusion of supraphysiological concentrations of CCK in rats, a treatment that induced tissue changes reminiscent of mild acute pancreatitis, likewise resulted in rapid displacement of Munc18c from the basal membrane in vivo.

Authors

Herbert Y. Gaisano, Manfred P. Lutz, Juergen Leser, Laura Sheu, Grit Lynch, Lan Tang, Yoshikazu Tamori, William S. Trimble, Anne Marie F. Salapatek

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Figure 3

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Confocal microscopy of a large acinus showing a 15-minute time course of...
Confocal microscopy of a large acinus showing a 15-minute time course of stimulation by 1 μM CCK-OPE. This is a projection of a series of Z-sections across the equatorial plane, which were digitally collapsed using Adobe Photoshop software (Adobe Systems Inc., San Jose, California, USA) to capture the vesicles of adjoining confocal planes. Arrow 1 indicates the acinar ductal lumen; arrow 2 points to its “neck” as it exits out of the acinus, which is marked by arrow 3. Note that the ductal zymogen protein contents are stained with FM1-43, which fills the ductal lumen. Here, 1 μM CCK-OPE stimulation caused a time-dependent (1–6 minutes) increase in fluorescence within the ductal lumen and an increase in the diameter of the lumen. Note tubular structures branching off from the ductal lumen that seem to extend into the apical surfaces of the acinar cells. At 6 minutes, the ductal lumen decreased in size, FM1-43 fluorescence intensity (compared with 4 minutes) decreased, and some of the tubular structures shrank or collapsed. At 15 minutes, the duct was “reduced” in size to resting levels. Note small FM1-43 fluorescent puncta inside the acinar cells at 15 minutes. Bar = 20 μm.