DEPRESSIONS ARE POROSOMES PRESENT IN SECRETORY CELLS

Cho, Sang-Joon and Jena, Bhanu P.

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

Our studies using the AFM reveal a new group of fixed plasma membrane structures called 'pits' and 'depressions', involved in secretion in various secretory cells. Acinar cells of the exocrine pancreas, growth hormone secreting cells of the pituitary, and chromaffin cells, all possess porosomes or depressions, at the cell plasma membrane. Following of secretion, secretory vesicles dock and transiently fuse at depressions, to release vesicular contents. 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. Using gold-tagged antobody against intragranular content, we demonstrates the release of secretory products at these 'pit' and 'depression' structures, demonstrating these to be fusion pores or porosomes, where membrane-bound secretory vesicles dock and fuse to release vesicular contents. This study was supported by grants from the NIH to BPJ.