The capacity of @entity9932 to modify the permeability barrier of cell membranes has been explored. Membrane efflux induced either by in situ generated @entity9932 (through enzymatic cleavage of @entity4291 ) or by addition of @entity9932 to preformed membranes has been studied. Large unilamellar vesicles composed of different phospholipids and @entity165 , and containing entrapped fluorescent molecules, have been used as a system to assay @entity2367 -dependent efflux. Small proportions of @entity2367 (10 mol % of total lipid) that may exist under physiological conditions of @entity2367 -dependent signaling have been used in most experiments. When long chain (egg-derived) @entity9932 are used, both externally added or enzymatically produced @entity9932 induce release of vesicle contents. However, the same proportion of @entity9932 generated by sphingomyelinase induce faster and more extensive efflux than when added in organic solution to the preformed vesicles. Under our conditions 10 mol % of @entity20283 ( @entity20283 ) did not induce any efflux. On the other hand, sphingomyelinase treatment of bilayers containing 50 mol % @entity4291 gave rise to release of @entity941 -derivatised dextrans of molecular mass approximately 20 kDa, i.e. larger than @entity4674 . These results have been discussed in the light of our own previous data (Ruiz-Arg  ello, M. B., Basa  ez, G., Go  i, F. M., and Alonso, A. (1996) J. Biol. Chem. 271, 26616-26621) and of the observations by Siskind and Colombini (Siskind, L. J., and Colombini, M. (2000) J. Biol. Chem. 275, 38640-38644). Our spectroscopic observations appear to be in good agreement with the electrophysiological studies of the latter authors. Furthermore, some experiments in this paper have been designed to explore the mechanism of @entity2367 -induced efflux. Two properties of @entity2367 , namely its capacity to induce negative monolayer curvature and its tendency to segregate into @entity2367 -rich domains, appear to be important in the membrane restructuring process.

Membrane restructuring via XXXX results in enhanced solute efflux.

@entity20283 :: ('MESH:C064769', 'Chemical') :: ['C(2)-ceramide', 'N-acetylsphingosine'] @entity4674 :: ('54205', 'Gene') :: ['cytochrome c'] @entity2367 :: ('CHEBI:17761', 'Chemical') :: ['ceramide'] @entity165 :: ('MESH:D002784', 'Chemical') :: ['cholesterol'] @entity941 :: ('MESH:D019793', 'Chemical') :: ['fluorescein'] @entity9932 :: ('MESH:D002518', 'Chemical') :: ['ceramides'] @entity4291 :: ('CHEBI:17636', 'Chemical') :: ['sphingomyelin']
@entity2367 :: (CHEBI:17761,Chemical) :: ['ceramide']
