A mechanical force contributes to the "osmotic swelling" of brush-border membrane vesicles

Swelling and penetration of fatty acid vesicles under ion-competitive environment

The physicochemical characteristics of fatty acid (FA) vesicles and their ion sensitivity as drug delivery vehicles in an ion-competitive environment have received much attention. Here, we show that in a Na+/K+ competitive ionic environment, FA vesicles undergo a cascade of periodic expansion and selective ion retention in response to osmotic attack. When the Na+/K+ ratio is altered, the expansion and volume of vesicles are affected and the ions in vesicles mix with the hyperosmotic fluid to produce a stable transmembrane potential, consistent with the Donnan effect and iontophoresis theory. Furthermore, osmotic swelling experiments suggest that FA vesicles are more easily maintained in a single Na+ or K+ solution than in a multicomponent ion competition system. As a theoretical basis for the utilization of FA vesicles in multicomponent ionic environments, we developed a core theoretical model to characterize the basic features of the volume fluctuations of FA vesicles in ion-competing environments.

Effection of Lactic Acid Dissociation on Swelling-Based Short-Chain Fatty Acid Vesicles Nano-Delivery

Functionalized small-molecule assemblies can exhibit nano-delivery properties that significantly improve the bioavailability of bioactive molecules. This study explored the self-assembly of short-chain fatty acids (FA, Cn < 8) to form novel biomimetic nanovesicles as delivery systems. Lactic acid is involved in the regulation of multiple signaling pathways in cancer metabolism, and the dissociation of lactic acid (LA) is used to regulate the delivery effect of short-chain fatty acid vesicles. The study showed that the dissociation of lactic acid caused pH changes in the solution environment inducing hydrogen ion permeability leading to rapid osmotic expansion and shape transformation of FA vesicles. The intrinsic features of FA vesicle formation in the LA environment accompanied by hydrogen ion fluctuations, and the appearance of nearly spherical vesicles were investigated by transmission electron microscopy (TEM) and Fourier Transform Infrared Spectroscopy (FTIR). Compared with the vesicle membrane built by surfactants, the FA/LA composite system showed higher permeability and led to better membrane stability and rigidity. Finally, membrane potential studies with the IEC cell model demonstrate that lactate dissociation capacity can effectively increase the cellular adsorption of FA vesicles. Altogether, these results prove that FA vesicles can function as a stand-alone delivery system and also serve as potential development strategies for applications in a lactate environment.

Multifusion-induced wall-super-thick giant multilamellar vesicles

A polymeric multivesicular system was created by hydrating a film. This system underwent multifusion events and eventually evolved into giant multilamellar vesicles with extremely thick walls. The semi-permeable wall and large size make these vesicles suitable for encapsulating living cells.

Kinetics of pore formation by the Bacillus thuringiensis toxin Cry1Ac

After binding to specific receptors, Cry toxins form pores in the midgut apical membrane of susceptible insects. The receptors could form part of the pore structure or simply catalyze pore formation and consequently be recycled. To discriminate between these possibilities, the kinetics of pore formation in brush border membrane vesicles isolated from Manduca sexta was studied with an osmotic swelling assay. Pore formation, as deduced from changes in membrane permeability induced by Cry1Ac during a 60-min incubation period, was strongly dose-dependent, but rapidly reached a maximum as toxin concentration was increased. Following exposure of the vesicles to the toxin, the osmotic swelling rate reached a maximum shortly after a delay period. Under these conditions, at relatively high toxin concentrations, the maximal osmotic swelling rate increased linearly with toxin concentration. When vesicles were incubated for a short time with the toxin and then rapidly cooled to prevent the formation of new pores before and during the osmotic swelling experiment, a plateau in the rate of pore formation was observed as toxin concentration was increased. Taken together, these results suggest that the receptors do not act as simple catalysts of pore formation, but remain associated with the pores once they are formed.