Comparison of the fusion membrane dynamics between large exocrine vesicles and smaller endocrine vesicles. (A and B) Fusion modes regarding Ω profile membrane size/shape changes and pore status in LSV of exocrine cells (A) and smaller endocrine vesicles (EndocV) in chromaffin cells (B). Note that different naming systems used in A and B may refer to the same fusion mode. (C and D) LSV (C) and EndocV (D) pore dynamics: competition between fusion pore expansion and constriction mechanisms determines the fusion pore dynamics, including expansion, constriction, and closure. A hemi-fusion structure is included in D because it is detectable during EndocV fusion and dynamin may antagonize hemi-to-full fusion. (E and F) Mechanisms underlying Ω profile shrinking and membrane crumpling for LSV (E) and EndocV fusion (F). ΔP, a positive osmotic pressure difference between intra- and extracellular solution; membrane flow, F-actin–supported tension at the plasma membrane reels in the low-tension Ω profile membrane, resulting in the shrinking of the Ω profile.