Release of diacylglycerol-enriched vesicles from erythrocytes with increased intracellular [Ca2+]

Membrane protein segregation during release of microvesicles from human erythrocytes

“…This achieves the accumulation of a glycopeptide component (possibly PAS-l) of the 4.1/4.2 region, and the exclusion of most other polypeptides, particularly band 3, from the small proportion of the membrane destined to become the 'tails'. It has been suggested that the initial blebbing of the erythrocyte membrane which precedes microvesicle release is driven by the accumulation of diacylglycerol produced by a Ca*-stimulated polyphosphoinositide phosphodiesterase at the inner surface of the membrane [3,8]. From the composition of the isolated 'tails', it now seems that the final membrane fusion event which leads to vesicle release may also require the elimination of some membrlne-spanning polypeptides, particularly band 3, from the region of fusion, as envisaged in the general model of fusion developed in [IO].…”

“…In previous studies of the release of cytoplasmftlled microvesicles from human red blood cells either during storage [ 1,2] or following treatment with Cap and the ionophore A23 187 [3] we have frequently observed slender protuberances ('tails') on many of the vesicles, but we have been uncertain whether they represented a genuine feature of microvesicle structure or an artefact of preparation for electron microscopy. The reality of these structures has now been confirmed using a variety of preparative techniques for electron microscopy and they have been isolated and their lipid and polypeptide composition determined.…”

“…Microvesicles were isolated from blood aged by storage [2] for 8-9 weeks and from 4-5 days old erythrocytes treated with Cap + ionophore A231 87 [3]. The microvesicles from 500 ml packed red blood cells were suspended in 20-30 ml Hepes-saline solution (150 mM NaCl, 1.5 mM Hepes, pH 7.0) and sonicated in an MSE sonicator set at 245 V, for 10-l 5 s at 1.5 A at 4°C.…”

Membrane Skeleton Detachment in Spherical and Cylindrical Microexovesicles

“…The shape of these vesicles is usually spherical but is also sometimes cylindrical (Hägerstrand and Isomaa, 1992). It was found that RBC vesicles are usually depleted in major components of the membrane skeleton (Allan et al, 1976;Wagner et al, 1986;Hägerstrand and Isomaa, 1994;Knowles et al, 1997). This depletion may be due to a disruption of the skeleton (Kozlov et al, 1990) or its detachment from the membrane prior to vesiculation (Liu et al, 1989;Iglič et al, 1995;Knowles et al, 1997;Bobrowska-Hägerstrand et al, 1998).…”

“…The redistributions of other membrane components, i.e., membrane lipids and integral membrane proteins, during the vesiculation process (Allan et al, 1976;Discher et al, 1994;Hägerstrand and Isomaa, 1994;Knowles et al, 1997) may play an important role in stabilization of the microexovesicle shape (Lipowsky, 1993;Kralj-Iglič et al, 1996;Seifert, 1997;Kralj-Iglič et al, 1999).…”