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 6

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Supramaximal CCK-evoked basal membrane exocytosis by a PKC-mediated path...
Supramaximal CCK-evoked basal membrane exocytosis by a PKC-mediated pathway. (a) A confocal section across the equatorial place of a four-cell acinus stained with FM1-43, which was preincubated with 1 nM TPA for 15 minutes 37°C and then combined with 1 μM CCK-OPE. Images were taken during the 1 nM TPA preincubation, and the fluorescence was identical to basal levels before exposure to TPA (not shown). Many of the basal membrane hotspots were already present prior to CCK-OPE stimulation and then increased in intensity and size after stimulation (filled arrowheads); only a few more de novo membrane hotspots appeared later (open arrowheads). Bar = 20 μm. (b) Epifluorescence microscopy (1 frame per second) performed on a doublet-cell acinus subjected to the same protocol of preincubation with 1 nM TPA, followed by addition of 1 μM CCK-OPE. A phase contrast image of the acinus and the regions of interest drawn on this acinus for analysis are shown. 0 time is when 1 μM CCK-OPE was added into the 1 nM TPA-containing media. The 15-minute TPA preincubation is not shown. Note the synchronous increase in the fluorescence intensity of the basal plasma membrane hotspots (B-PM1 and B-PM2); in contrast, there was no change in the FM1-43 fluorescence intensity in the apex or ZG poles of the acinus. (c) A graphical summary of the peak fluorescence data obtained from several confocal experiments performed as in a (n = 15 basal membrane hotspots from 9 cells; three separate experiments).