A permanent cup-shaped structure at the cell plasma membrane in secretory cells. Following a secretory stimulus, secretory vesicles transiently dock and fuse at the base of porosomes and release intravesicular contents dictated by the turgor pressure generated from the swelling of secretory vesicles. [ http://www.ncbi.nlm.nih.gov/pubmed/16563225 http://www.ncbi.nlm.nih.gov/pubmed/15090256 ]