Fusion pore stability of peptidergic vesicles

Abstract

It is believed that in regulated exocytosis the vesicle membrane fuses with the plasma membrane in response to a physiological stimulus. However, in the absence of stimulation, repetitive transient fusion events are also observed, reflecting a stable state. The mechanisms by which the initial fusion pore attains stability are poorly understood. We modelled energetic stability of the fusion pore by taking into account the anisotropic, intrinsic shape of the membrane constituents and their in-plane ordering in the local curvature of the membrane. We used cell-attached membrane capacitance techniques to monitor the appearance and conductance of single fusion pore events in cultured rat lactotrophs. The results revealed a bell-shaped distribution of the fusion pore conductance with a modal value of 25 pS. The experimentally observed increase of the fusion pore stability with decreasing fusion pore radius agrees well with the theoretical predictions. Moreover, the results revealed a correlation between the amplitude of transient capacitance increases and the fusion pore conductance, indicating that larger vesicles may attain a stable fusion pore with larger fusion pore diameters.

Local electrostatic interactions determine the diameter of fusion pores

“…38 A fraction of reversible events exhibit a measurable (narrow) fusion pore conductance, which is discerned by the projection between the imaginary (Im) and the real (Re) parts of admittance signals. 29 In controls half of the reversible events exhibited projections to the Re trace ( Fig. 2A).…”

“…28 However, it is safe to assume that anisotropic membrane constituents (proteins, lipids or other nanodomains) can attribute to its stability. 29,30 The constituents of biological membranes (lipids, glycoproteins, glycolipids, etc.) frequently carry one or more ionized or polar groups 17 and are influenced by local cation clouds.…”

Exploring the binding dynamics of BAR proteins

“…In exocytosis the merger of the vesicle and plasma membranes leads to formation of the fusion pore. The fusion pore is an aqueous channel connecting the vesicle lumen with the extracellular medium and is most likely a region of high curvature [30]. As such, it is an ideal membrane region where BAR proteins could potentially contribute to its formation, stability or even to the transition from the narrow diameter intermediate fusion pore state to either a) complete dilation (full-fusion exocytosis), or b) subsequent closure (transient exocytosis).…”

“…This experiment would include C m measurements in a whole-cell configuration. On the other hand, cell-attached C m measurements [30] (Fig. 5B) would reveal elementary fusion pore properties (i.e.…”

Suppression of membrane vesiculation as anticoagulant and anti-metastatic mechanism. Role of stability of narrow necks

“…Recently, another membranous pool -spontaneously stable membranous nanostructures -has been recognized in cells Isomaa 1989, 1992;Rustom et al 2004;Schara et al 2009; and also in phospholipid systems (Mathivet et al 1996;KraljIglič et al 2001;Iglič et al 2003;Mareš et al 2008;. Such structures are for example buds (Kralj-Iglič et al 2000, nanotubules , Iglič et al 2003Rustom et al 2004;Galkina et al 2005;Gimsa et al 2007;Veranič et al 2008), nanovesicles Isomaa 1989, 1992;Junkar et al 2009;Mrvar-Brečko et al 2010;Šuštar et al 2011a, b) and narrow necks Iglič et al 2007;Jorgačevski et al 2010).…”