Interplay between membrane dynamics, diffusion and swelling pressure governs individual vesicular exocytotic events during release of adrenaline by chromaffin cells

The Effects of Vesicular Volume on Secretion through the Fusion Pore in Exocytotic Release from PC12 Cells

“…The fusing dense-core vesicle in Figure 1 E (black arrow) suggests that such secretory granule swelling may have been underway at the time of fixation. It has been hypothesized and supported experimentally that this type of swelling may serve to impart a mechanical pressure on the interior vesicular wall in cell types such as chromaffin cells, where the dense core fills the vesicle (Amatore et al, 2000). In systems like the PC12 cell where the dense core fills only a portion of the vesicle, however, expansion of the core is more likely to result in enhanced pressure-driven mass transport through the fusion pore and fluidic pressure on the interior vesicle walls.…”

“…To better understand how vesicular volume changes might regulate exocytotic release through the fusion pore, we have pharmacologically manipulated vesicular volume and examined the amperometric features preceding catecholamine secretion events from rat pheochromocytoma (PC12) cells. Although Alvarez de Toledo et al (1993) and Amatore et al (2000) have hypothesized a relationship between the size of secretory vesicles and the characteristics of amperometric foot events, experimental data that directly support this theory have been lacking. The amount and duration of neurotransmitter released in the foot portion of the event are directly related to vesicular volume; however, there is an inverse relationship between vesicle volume and the frequency of observed foot events, as well as the percentage of vesicular content released during the foot portion of the event.…”

Insulin granule dynamics in pancreatic beta cells

“…The slow release of the peptide cargo could result from its slow dissociation from the intragranular matrix, the properties of which in the insulin granule remain poorly defined. Such a scenario is suggested by analogy to the release of catecholamines from chromaffin cells, where ion exchange via the fusion pore leads to matrix swelling that provides the tension which eventually leads to the opening of an aperture between the granule lumen and the extracellular space large enough to allow complete granule emptying [40,91]. Irrespective of the underlying reason, these observations suggest that release of high molecular weight substances (such as insulin) is about 25-fold slower than the time course of capacitance increase [88].…”

A Fast Mode of Membrane Fusion Dependent on Tight SNARE Zippering

“…What drives fusion pore enlargement? Membrane tension and pore lengthening were both proposed to lower energy barriers that prevent spontaneous fusion pore dilation (Chizmadzhev et al, 1995(Chizmadzhev et al, , 2000Amatore et al, 2000). Membrane tension may result both from the interaction of synaptotagmins with SNAREs and phospholipids at the neck of the fusing vesicle and from swelling of the granule matrix.…”

“…Membrane tension may result both from the interaction of synaptotagmins with SNAREs and phospholipids at the neck of the fusing vesicle and from swelling of the granule matrix. Influx of Na ϩ through the fusion pore displaces matrix-bound Ca 2ϩ and catecholamines, and leads to matrix swelling and increased vesicular membrane tension (Amatore et al, 2000;Gong et al, 2007). Energy would be stored in the membrane until the tension exceeds the cohesion of the fusion machinery and would then drive pore enlargement.…”