NEW STRUCTURES INVOLVED IN MEMBRANE FUSION

Jena, Bhanu P., and Cho, S-J.

Department of Physiology & Pharmacology, Wayne State University School of Medicine, Detroit, MI 48201, USA.

Our studies using the AFM reveal a new group of plasma membrane structures involved in exocytosis in live pancreatic acinar cells. In resting acinar cells, 'pits' measuring 0.5 - 2 micrometer and containing 3-20 'depressions' measuring 100-180 nanometers in diameter, were identified only at the apical plasma membrane of acinar cells where secretion occurs. Following stimulation of secretion, 'depressions' dialated, returning to resting size following completion of secretion. Our study reveals 'depressions' structures to be under regulation of actin. Studies using gold-labeled intragranular content demonstrates the release of secretory products at 'pits' and 'depressions'. These studies demonstrate that 'pits' and 'depressions' are sites at the apical plasma membrane in live cells, where membrane-bound secretory vesicles dock and fuse to release vesicular contents. This study was supported by grants from the NIH to BPJ.