Myosin I is associated with zymogen granule membranes in the rat pancreatic acinar cell.
OBJECTIVE
The mechanisms whereby intracellular messengers mediate zymogen granule transport and exocytosis in the pancreatic acinar cell are not well defined. Electron microscopy has shown a periluminal network of actin in the acinar cell, suggesting a role for actin and myosin in the transport process. The possible involvement of two types of myosin in the secretory process was investigated, and their distribution in acinar cells was determined.


METHODS
Antibodies specific to myosin I or to myosin II were used for immunocytochemistry and Western blot analysis. Ultrastructural studies were also performed.


RESULTS
Western blot analysis showed that myosin I and myosin II were present in total pancreatic homogenate but that only myosin I was present on isolated zymogen granules and their membranes. By immunocytochemistry, myosin I was shown in the apical aspect of acinar cells colocalized with glycoprotein 2, a marker for zymogen granules, and actin. By immunocytochemistry, myosin I was also localized on isolated zymogen granules.


CONCLUSIONS
The immunolocalization of myosin I to zymogen granule membranes and its close association with periluminal actin suggest that myosin I plays a direct role in the process of transport and exocytosis of zymogen granules in the pancreatic acinar cell.
Poucell-Hatton
S
S
Department of Medicine, San Diego Microscopy and Imaging Resource, University of California San Diego, USA.
Perkins
P S
PS
Deerinck
T J
TJ
Ellisman
M H
MH
Hardison
W G
WG
Pandol
S J
SJ
D000199:Actins / Q000032:analysis / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000032:analysis / Q000276:immunology; D015153:Blotting, Western; D003594:Cytoplasmic Granules / Q000737:chemistry* / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D004792:Enzyme Precursors / Q000032:analysis*; D005089:Exocytosis / Q000502:physiology; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000032:analysis / Q000502:physiology; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D009218:Myosins / Q000032:analysis* / Q000276:immunology / Q000502:physiology; D010179:Pancreas / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D000199:Actins; D000906:Antibodies; D004792:Enzyme Precursors; D008565:Membrane Proteins; D009218:Myosins