Figure 2.

(A) Initial state of vesicle (radius R_v) and plasma membrane. The membrane to be incorporated into a fusion pore is blue. The proteinaceous pore is indicated by two dotted rectangles. (B) Vesicle and plasma membrane connected by a lipidic fusion pore (green). The dotted horizontal line indicates the plane where the pore is narrowest. (C) A blow-up of the lipidic fusion pore shows key pore dimensions including the pore radius, R_p, the horizontal extension of the pore, R_h, and the distance along a radius through the pore-vesicle junction from the vesicle membrane to the horizontal plane, R_m. Appendix A derives an expression for the elastic energy of a fusion pore using these geometric parameters.