Abstract
Agonist-induced cytosolic Ca2+ (Ca2+i) signals begin as apical-to-basal Ca2+i waves in pancreatic acinar cells and in other polarized epithelia. However, the basis of this polarized Ca2+i signaling pattern is unknown. Here we use immunocytochemistry to demonstrate that the type 3 inositol trisphosphate receptor is localized to the extreme apex of pancreatic acinar cells, the region which corresponds to the trigger zone from which Ca2+i signals originate in this cell type (Kasai, H., Li, Y.X., and Miyashita, Y. (1993) Cell 74, 669-677). We also show that inositol trisphosphate-mediated Ca2+ release induces amylase release from permeabilized pancreatic acini. Since Ca2+i signals begin by inositol trisphosphate-mediated Ca2+ release, these findings suggest that localization of the type 3 inositol trisphosphate receptor to the trigger zone is responsible for the generation of apical-to-basal Ca2+i waves, and that this organization may be important for regulating apical exocytosis in pancreatic acinar cells.
Highlights
Medicine, New Haven, Connecticut 06510,the rodent chow under a constant light cycle and used for all experiments
X., and and GST-H1CTcontain 12identical amino acids at the NH2ends of the Miyashita, Y. (1993)Cell 74, 669877).We show that segments derived from their respective InsP,Rs, as shown below, the inositoltrisphosphate-mediatedCa2+releaseinduces antisera aH3CT and aHlCT are highly specific for the full-length rat amylaserelease frompermeabilizedpancreaticacini
Diated Ca2+ release, these findings suggest that locaTlhizeaa-pical region of acinar cells wasidentified using antibody SG7C12, tion of the type 3 inositol trisphosphate receptor to the a mouse monoclonal antibody raised against a secretory carrier memtrigger zoneis responsible for the generatioonf apicalto-basal Ca2+i waves, and that this organizamtioayn be important for regulating apical exocytoinsips ancreatic brane protein (SCAMP) found onthe cytoplasmicside of parotid apical secretory vesicles, and on pancreatic exocrine granules [11]
Summary
New Haven, Connecticut 06510,the rodent chow under a constant light cycle and used for all experiments. To determine the subcellular distribution of the type 3 InsP,R, specimens were double-labeled with aH3CT and antibody SG7C12. Negative controls foInrsP,R labeling were stained with aH3CT antiserum purified against GST alone (as described above), and with rhodamine-conjugated goat anti-rabbit antibodies.
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