cells can be discarded by low-speed centrifugation and later the fraction of the known origin (plasmalemma, tonoplast, etc.) can be isolated by precise high-speed centrifugation in the density gradient. Using osmotic shock, it is possible temporarily open vesicles (filling them with the required solution) and then centrifugate down again and resuspend in a different solution. Applying ionophores like valinomycin can create electrochemical gradients comparable to the gradients inside living cells. Vesicles are mainly used in two types of research: To find and later isolate membrane receptors that specifically bind hormones and various other important substances. To investigate transport of various ions or other substances across the membrane of the given type. While transport can be more easily investigated with patch clamp techniques, vesicles can also be isolated from objects for which a patch clamp is not applicable. Artificial vesicles Artificial vesicles are classified into three groups based on their size: small unilamellar liposomes/vesicles (SUVs) with a size range of 20–100 nm, large unilamellar liposomes/vesicles (LUVs) with a size range of 100–1000 nm and giant unilamellar liposomes/vesicles (GUVs) with a size range of 1–200 µm. Smaller vesicles in the same size range as trafficking vesicles found in living cells are frequently used in biochemistry and related fields. For such studies, a homogeneous phospholipid vesicle suspension can be prepared by extrusion or sonication, or by rapid injection of a phospholipid solution into an aqueous buffer solution. In this way, aqueous vesicle solutions can be prepared of different phospholipid composition, as well as different sizes of vesicles. Larger synthetically made vesicles such as GUVs are used for in vitro studies in cell biology in order to mimic cell membranes. These vesicles are large enough to be studied using traditional fluorescence light microscopy. A variety of methods exist to encapsulate biological reactants like protein solutions within such vesicles, making GUVs an ideal system for the in vitro recreation (and investigation) of cell functions in cell-like model membrane environments. These methods include microfluidic methods, which allow for a high-yield production of vesicles with consistent sizes. See also Bleb (cell biology) Host-pathogen interface Membrane contact sites Membrane nanotube Membrane vesicle trafficking Micelle Microsome Protocell Spitzenkörper, a structure of many small vesicles found in fungal hyphae References Further reading External links Lipids, Membranes and Vesicle Trafficking - The Virtual Library of Biochemistry, Molecular Biology and Cell Biology Membrane biology Organelles