Research Article

Fusion Pore Diameter Regulation by Cations Modulating Local Membrane Anisotropy

Figure 3

Schematic model for the rhythmic opening and closure of the fusion pore. The stable fusion pore of a vesicle can either be in open or closed states (a). The influx of cations via ion channels in the vesicle membrane is constant, while the efflux through the fusion pore out of the vesicle is allowed only when the fusion pore is open (see insets). The spontaneous curvature at the fusion pore is modulated by the cation concentration in the vesicle. The membrane force, derived from the differentiation of the system free energy, is exerted in the radial direction (see arrows) of the modelled axisymmetric fusion pore (see insets). The fusion pore is composed of a single anisotropic membrane domain (b). The membrane spontaneous curvature ( 𝐻 𝑚 ) of the fusion pore is plotted as a function of the relative cation concentration ( 𝑛 + / 𝑛 + m a x ) (c). The proposed dynamics is that the cation flux through the vesicle increases the cation concentration in the vesicle, which then reduces the intrinsic membrane curvature ( 𝐻 𝑚 ) leading to the opening of the fusion pore. The opening of the pore causes the abrupt reduction in cation concentration, which increases the spontaneous membrane curvature of the pore leading to the abrupt closing of the fusion pore.
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