Control of granule mobility and exocytosis by Ca2+ -dependent formation of F-actin in pancreatic duct epithelial cells.
Elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) triggers exocytosis of secretory granules in pancreatic duct epithelia. In this study, we find that the signal also controls granule movement. Motions of fluorescently labeled granules stopped abruptly after a [Ca(2+)](i) increase, kinetically coincident with formation of filamentous actin (F-actin) in the whole cytoplasm. At high resolution, the new F-actin meshwork was so dense that cellular structures of granule size appeared physically trapped in it. Depolymerization of F-actin with latrunculin B blocked both the F-actin formation and the arrest of granules. Interestingly, when monitored with total internal reflection fluorescence microscopy, the immobilized granules still moved slowly and concertedly toward the plasma membrane. This group translocation was abolished by blockers of myosin. Exocytosis measured by microamperometry suggested that formation of a dense F-actin meshwork inhibited exocytosis at small Ca(2+) rises <1 microm. Larger [Ca(2+)](i) rises increased exocytosis because of the co-ordinate translocation of granules and fusion to the membrane. We propose that the Ca(2+)-dependent freezing of granules filters out weak inputs but allows exocytosis under stronger inputs by controlling granule movements.
Jung
Seung-Ryoung
SR
Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA.
Kim
Mean-Hwan
MH
Hille
Bertil
B
Koh
Duk-Su
DS
D000199:Actins / Q000378:metabolism*; D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D005456:Fluorescent Dyes / Q000378:metabolism; D006801:Humans; D020409:Molecular Motor Proteins / Q000378:metabolism; D009077:Mucins / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D010183:Pancreatic Ducts / Q000166:cytology*; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D053778:Thiazolidines / Q000378:metabolism; D014544:Uridine Triphosphate / Q000378:metabolism
D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; C073804:FM1 43; D005456:Fluorescent Dyes; D020409:Molecular Motor Proteins; D009077:Mucins; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D053778:Thiazolidines; D009218:Myosins; C037068:latrunculin B; D002118:Calcium; D014544:Uridine Triphosphate