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 5

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Supramaximal CCK (10 nM) stimulation redirects exocytosis from the apica...
Supramaximal CCK (10 nM) stimulation redirects exocytosis from the apical to the basal plasma membrane. (a) A confocal section across the equatorial plane of a four-cell acinus stained with FM1-43, which was stimulated by 10 nM CCK-8 for 1, 5, and 15 minutes compared with the basal state. Note that most of the membrane hotspots were already present in the cells prior to stimulation (indicated by filled arrowheads) and then increased in intensity and size after stimulation. De novo hotspots not previously present also appeared with CCK stimulation (open arrowheads in the 1-minute image). Bar = 20 μm. (b and c) Epifluorescence microscopy of a small triplet-cell pancreatic acinus stimulated by 10 nM CCK-8. Real-time changes in fluorescence were obtained at 1 frame/sec. (b) The fluorescence images at 0 time, 40 seconds, 2 minutes, and 10 minutes of stimulation. (c) Regions of interest were drawn as indicated on this diagram of the acinus shown in b. The left fluorescence tracing shows two representative hotspots that were present at basal state (filled arrowheads). The right fluorescence tracing shows two de novo hotspots (open arrowheads, see 40-second image in b). (d and e) Graphical summaries of the peak fluorescence data from (d) epifluorescence studies (12 cells, four experiments as in c), including the two populations of basal plasma membrane (B-PM) hotspots (n = 26 each, indicated by filled and open arrowheads), and (e) confocal studies (13 cells, three experiments as in a) of 10 nM CCK-8–evoked basal membrane FM1-43 exocytosis (n = 18 hotspots) at 1, 5, and 15 minutes of stimulation.