Experiments have been performed to examine the hypothesis that submembrane fusion-to-cell membranes is driven by granular osmotic pressure, vesicular swelling, and membrane perforation at the point of contact between granular vesicle and cell membrane. The data generated so far are consistent with the idea that a secretory granule must swell to fuse with the plasma membrane and support the hypothesis of an osmotically driven fusion step during exocytosis.
