title: Accumulated bending energy elicits neutral sphingomyelinase activity in human red blood cells.
abstract: We propose that accumulated membrane bending energy elicits a neutral sphingomyelinase (SMase) activity in human erythrocytes. Membrane bending was achieved by osmotic or chemical processes, and SMase activity was assessed by quantitative thin-layer chromatography, high-performance liquid chromatography, and electrospray ionization-mass spectrometry. The activity induced by hypotonic stress in erythrocyte membranes had the pH dependence, ion dependence, and inhibitor sensitivity of mammalian neutral SMases. The activity caused a decrease in SM contents, with a minimum at 6 min after onset of the hypotonic conditions, and then the SM contents were recovered. We also elicited SMase activity by adding lysophosphatidylcholine externally or by generating it with phospholipase A(2). The same effect was observed upon addition of chlorpromazine or sodium deoxycholate at concentrations below the critical micellar concentration, and even under hypertonic conditions. A unifying factor of the various agents that elicit this SMase activity is the accumulated membrane bending energy. Both hypo-and hypertonic conditions impose an increased curvature, whereas the addition of surfactants or phospholipase A(2) activation increases the outer monolayer area, thus leading to an increased bending energy. The fact that this latent SMase activity is tightly coupled to the membrane bending properties suggests that it may be related to the general phenomenon of stress-induced ceramide synthesis and apoptosis.
authors: Unidad de Biofísica (Centro Mixto CSIC-UPV/EHU) and Departamento de Bioquímica, Universidad País Vasco, Spain.
authors: David J
authors: DJ
authors: López
authors: Meritxell
authors: M
authors: Egido-Gabas
authors: Iván
authors: I
authors: López-Montero
authors: Jon V
authors: JV
authors: Busto
authors: Josefina
authors: J
authors: Casas
authors: Marie
authors: M
authors: Garnier
authors: Francisco
authors: F
authors: Monroy
authors: Banafshé
authors: B
authors: Larijani
authors: Félix M
authors: FM
authors: Goñi
authors: Alicia
authors: A
authors: Alonso
mesh_terms: D002478:Cells, Cultured; D004735:Energy Transfer / Q000502:physiology*; D004789:Enzyme Activation; D004910:Erythrocyte Membrane / Q000502:physiology* / Q000648:ultrastructure*; D006801:Humans; D008560:Membrane Fluidity / Q000502:physiology*; D008563:Membrane Lipids / Q000502:physiology*; D013108:Sphingomyelin Phosphodiesterase / Q000737:chemistry* / Q000648:ultrastructure
chemical_list: D008563:Membrane Lipids; D013108:Sphingomyelin Phosphodiesterase