MYOSIN-I IS ASSOCIATED WITH ZYMOGEN GRANULE MEMBRANES IN THE RAT PANCREATIC ACINAR CELL

Background & Aims: The mechanisms whereby intracellular messengers med iate zymogen granule transport and exocytosis in the pancreatic acinar cell are not well defined, Electron microscopy has shown a perilumina l network of actin in the acinar cell, suggesting a role for actin and myosin in the transport process, The possible involvement of two type s of myosin in the secretory process was investigated, and their distr ibution in acinar cells was determined, Methods: Antibodies specific t o myosin I or to myosin II were used for immunocytochemistry and Weste rn blot analysis, Ultrastructural studies were also performed, Results : Western blot analysis showed that myosin I and myosin II were presen t in total pancreatic homogenate but that only myosin I was present on isolated zymogen granules and their membranes, By immunocytochemistry , myosin was shown in the apical aspect of acinar cells colocalized wi th glycoprotein 2, a marker for zymogen granules, and actin, By immuno cytochemistry, myosin I was also localized on isolated zymogen granule s, Conclusions: The immunolocalization of myosin I to zymogen granule membranes and its close association with periluminal actin suggest tha t myosin I plays a direct role in the process of transport and exocyto sis of zymogen granules in the pancreatic acinar cell.