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The aim of this study was to determine the potential fertilizing of spermatozoa from the epididymal tail in different periods of time post-orchiectomy (P-OQ). Therefore, the study was approached in two stages. In the first stage, the orchiectomy was performed in 30 adult pigs. The testicles were stored at 5.00 ËšC in physiological saline solution for 5, 24, 48, 72, 96 and 120 hr. The spermatozoa were obtained by backflushing the vas deferens. The spermogram and fluorometric study were performed for each sample to evaluate the exposure of phosphatidylserine (PS) and acrosome reaction (AR). The second stage included the fertilization test, 16 prepubertal sows were selected, after synchronizing the oestrous cycle and the post-cervical artificial insemination was performed with the refrigerated sperm samples from each P-OQ time. The percentage of live sperm remained without significant changes until 96 hr P-OQ. An increase in the percentage of spermatozoa that showed a PS exposure was observed. The premature AR was evident after 72 hr. Considering that the artificial insemination was performed ensuring a minimum number of live sperms, no significant differences were observed in the number of embryos and corpora lutea. The results indicated that pig sperm collected from the epididymal tail P-OQ and stored for 5 and up to 72 hr at 5.00 ËšC had viable characteristics and maintained their fertilization ability. However, there was an increase in the loss of phospholipid asymmetry of the plasma membrane as time increased (72 and 96 hr), therefore, sperm viability was decreased. [ABSTRACT FROM AUTHOR]

We have found that group VIA calcium-independent phospholipase A2 (iPLA2β) has specificity for hydrolysis of phosphatidylethanolamine (PE) in mouse livers. Phospholipids (PLs) are transported to plasma membrane and some PLs including PE are externalized to maintain membrane PL asymmetry. Here we demonstrated that hepatocytes of iPLA2β-null (KO) mice showed an increase in PE containing palmitate and oleate. We aimed to examine whether externalization of PE on the outer leaflets could be affected by iPLA2β deficiency and its modulation by reactive oxygen species (ROS) or apoptosis. As duramycin has high affinity to PE, we used duramycin conjugated with biotin (DLB) and streptavidin 488 as a probe for detection of externalized PE. Compared to WT, naïve KO hepatocytes showed an increase in both PE externalization and ROS generation. These events were observed in male but not in female KO mice. Hydrogen peroxide or menadione treatment enhanced PE externalization to the same extent for both male/female WT and KO hepatocytes. By indirect immunofluorescence, DLB-streptavidin staining was observed as small punctuated spots on the cell surface of menadione-treated KO hepatocytes. Unlike the reported PS externalization, CD95/FasL treatment did not lead to any increase in PE externalization, and iPLA2β deficiency-dependent PE externalization was also not correlated with apoptosis. Thus, constitutive (but not induced) ROS generation in iPLA2β-deficient hepatocytes leads to PE externalization observed only in male mice. Such PE externalization may imply detrimental effects regarding further oxidation of PE fatty acids and the binding with pathogens on the outer leaflets of hepatocyte plasma membrane. [ABSTRACT FROM AUTHOR]

Type 4 P-type ATPases (P4-ATPases) function as phospholipid flippases, which translocate phospholipids from the exoplasmic leaflet to the cytoplasmic leaflet of the lipid bilayer, to generate and maintain asymmetric distribution of phospholipids at the plasma membrane and endosomal/Golgi membranes. The budding yeast Saccharomyces cerevisiae has four heteromeric flippases (Drs2p, Dnf1p, Dnf2p, and Dnf3p), associated with the Cdc50p family noncatalytic subunit, and one monomeric flippase, Neo1p. They have been suggested to function in vesicle formation in membrane trafficking pathways, but details of their mechanisms remain to be clarified. Here, to search for novel factors that functionally interact with flippases, we screened transposon insertional mutants for strains that suppressed the cold-sensitive growth defect in the cdc50Δ mutant. We identified a mutation of YMR010W encoding a novel conserved membrane protein that belongs to the PQ-loop family including the cystine transporter cystinosin and the SWEET sugar transporters. We named this gene CFS1 (cdc fifty suppressor 1). GFP-tagged Cfs1p was partially colocalized with Drs2p and Neo1p to endosomal/late Golgi membranes. Interestingly, the cfs1Δ mutation suppressed growth defects in all flippase mutants. Accordingly, defects in membrane trafficking in the flippase mutants were also suppressed. These results suggest that Cfs1p and flippases function antagonistically in membrane trafficking pathways. A growth assay to assess sensitivity to duramycin, a phosphatidylethanolamine (PE)-binding peptide, suggested that the cfs1Δ mutation changed PE asymmetry in the plasma membrane. Cfs1p may thus be a novel regulator of phospholipid asymmetry.

Using APPNLh/APPNLh x PS-1P246L/PS-1P246L human double knock-in (APP/PS-1) mice, we examined whether phosphatidylserine (PtdSer) asymmetry is significantly altered in brain of this familial Alzheimer disease mouse model in an age-dependent manner as a result of oxidative stress, toxic Aβ(1-42) oligomer production, and/or apoptosis. Annexin V (AV) and NBD-PS fluorescence in synaptosomes of wild-type (WT) and APP/PS-1 mice were used to determine PtdSer exposure with age, while Mg2+ ATPase activity was determined to correlate PtdSer asymmetry changes with PtdSer translocase, flippase, activity. AV and NBD-PS results demonstrated significant PtdSer exposure beginning at 9 months compared to 1-month-old WT controls for both assays, a trend that was exacerbated in synaptosomes of APP/PS-1 mice. Decreasing Mg2+ ATPase activity confirms that the age-related loss of PtdSer asymmetry is likely due to loss of flippase activity, more prominent in APP/PS-1 brain. Two-site sandwich ELISA on SDS- and FA-soluble APP/PS-1 brain fractions were conducted to correlate Aβ(1–40) and Aβ(1–42) levels with age-related trends determined from the AV, NBD-PS, and Mg2+ ATPase assays. ELISA revealed a significant increase in both SDS- and FA-soluble Aβ(1–40) and Aβ(1–42) with age, consistent with PtdSer and flippase assay trends. Lastly, because PtdSer exposure is affected by pro-apoptotic caspase-3, levels of both latent and active forms were measured. Western blotting results demonstrated an increase in both active fragments of caspase-3 with age, while levels of pro-caspase-3 decrease. These results are discussed with relevance to loss of lipid asymmetry and consequent neurotoxicity in brain of subjects with Alzheimer disease.

Oxidative stress, a hallmark of Alzheimer disease (AD), has been shown to induce lipid peroxidation and apoptosis disrupting cellular homeostasis. Normally, the aminophospholipid phosphatidylserine (PtdSer) is asymmetrically distributed on the cytosolic leaflet of the lipid bilayer. Under oxidative stress conditions, asymmetry is altered, characterized by the appearance of PtdSer on the outer leaflet, to initiate the first stages of an apoptotic process. PtdSer asymmetry is actively maintained by the ATP-dependent translocase flippase, whose function is inhibited if covalently bound by lipid peroxidation products, 4-hydroxynonenal (HNE) and acrolein, within the membrane bilayer in which they are produced. Additionally, pro-apoptotic proteins Bax and caspase-3 have been implemented in the oxidative modification of PtdSer resulting in subsequent asymmetric collapse, while anti-apoptotic protein Bcl-2 has been found to prevent this process.The current investigation focused on detection of PtdSer on the outer leaflet of the bilayer in synaptosomes from brain of subjects with AD and amnestic mild cognitive impairment (MCI), as well as expression levels of apoptosis-related proteins Bcl-2, Bax, and caspase-3. Fluorescence and Western blot analysis suggest PtdSer exposure on the outer leaflet is significantly increased in brain from subjects with MCI and AD contributing to early apoptotic elevation of pro- and anti-apoptotic proteins and finally neuronal loss. MCI is considered a possible transition point between normal cognitive aging and probable AD. Brain from subjects with MCI is reported to have increased levels of tissue oxidation; therefore, the results of this study could mark the progression of patients with MCI into AD. This study contributes to a model of apoptosis-specific oxidation of phospholipids consistent with the notion that PtdSer exposure is required for apoptotic-cell death.

Phospholipases play a key role in the metabolism of phospholipids and in cell signaling. They are also a very useful tool to explore phospholipid structure and metabolism as well as membrane organization. They are at the center of this review, covering a period starting in 1971 and focused on a number of subjects in which my colleagues and I have been involved. Those include determination of phospholipid asymmetry in the blood platelet membrane, biosynthesis of lysophosphatidic acid, biochemistry of platelet-activating factor, first attempts to define the role of phosphoinositides in cell signaling, and identification of novel digestive (phospho)lipases such as pancreatic lipase-related protein 2 (PLRP2) or phospholipase B. Besides recalling some of our contributions to those various fields, this review makes an appraisal of the impressive and often unexpected evolution of those various aspects of membrane phospholipids and lipid mediators. It is also the occasion to propose some new working hypotheses. [ABSTRACT FROM AUTHOR]

Cholesterylphosphoserine (CPHS) is a synthetic ester of cholesterol showing immunosuppressive activity. In the present study, we have used the T cell line Jurkat to investigate its mechanism of action. CPHS incorporates into cells reaching a molar ratio of 0.23 and 3.9 with the total phospholipid and cholesterol content, without inducing necrosis or apoptosis. CPHS incorporation elicits a dose-dependent binding of fluorescein isothiocyanate-labeled annexin V, suggesting that the steroid distributes in the external leaflet of plasma membrane exposing the phosphoserine group to the external cell environment and inserting the steroid ring into the phospholipid bilayer. In agreement with a preferential steroid association with sphingolipids, CPHS is included in a Triton X-100-insoluble complex when mixed with sphingomyelin and cholesterol. CPHS incorporation inhibits the esterification of low density lipoprotein (LDL)-derived cholesterol, producing a minor influence on the endogenous synthesis of cholesterol and on the acyl-CoA:cholesterol acyltransferase activity. In this effect, CPHS is as potent as progesterone (IC50 of 3.5 μm). It is concluded that the insertion of cholesterylphosphoserine (CPHS) in the Jurkat plasma membrane neutralizes the asymmetric distribution of the phosphoserine group and inhibits the movement of cholesterol to the endoplasmic reticulum. As CPHS is a negatively charged steroid, this last effect may be linked to the perturbation of sphingolipid/cholesterol-based microdomains, proposed to play a role in cholesterol trafficking.—Cusinato, F., W. Habeler, F. Calderazzo, F. Nardi, and A. Bruni. Loss of phosphoserine polar group asymmetry and inhibition of cholesterol transport in Jurkat cells treated with cholesterylphosphoserine.

Phospholipid composition of biological membranes differs between the cytoplasmic and exoplasmic leaflets. The type 4 P-type ATPases are phospholipid flippases that generate such membrane phospholipid asymmetry. Drs2p, a flippase in budding yeast, is involved in the endocytic recycling pathway. Drs2p is implicated in clathrin-coated vesicle formation, but the underlying mechanisms are not clearly understood. Here we show that the carboxyl-terminal cytoplasmic region of Drs2p directly binds to Rcy1p, an F-box protein that is also required for endocytic recycling. The Drs2p-binding region was mapped to the amino acids 574–778 region of Rcy1p and a mutant Rcy1p lacking this region was defective in endocytic recycling of a v-SNARE Snc1p. We isolated Drs2p point mutants that reduced the interaction with Rcy1p. The mutation sites were clustered within a small region (a.a. 1260–1268) of Drs2p. Although these point mutants did not exhibit clear phenotypes, combination of them resulted in cold-sensitive growth, defects in endocytic recycling of Snc1p and defective localization of Rcy1p to endosomal membranes like the drs2 null mutant. These results suggest that the interaction of Drs2p with Rcy1p plays an important role for Drs2p function in the endocytic recycling pathway. [ABSTRACT FROM PUBLISHER]

Flippases (type 4 P-type ATPases) are believed to translocate phospholipids from the exoplasmic to the cytoplasmic leaflet in bilayer membranes. Since flippases are structurally similar to ion-transporting P-type ATPases such as the Ca2+ ATPase, one important question is how flippases have evolved to transport phospholipids instead of ions. We previously showed that a conserved membrane protein, Cdc50p, is required for the endoplasmic reticulum exit of the Drs2p flippase in yeast. However, Cdc50p is still associated with Drs2p after its transport to the endosomal/trans-Golgi network (TGN) membranes, and its function in the complex with Drs2p is unknown. In this study, we isolated novel temperature-sensitive (ts) cdc50 mutants whose products were still localized to endosomal/TGN compartments at the non-permissive temperature. Mutant Cdc50 proteins colocalized with Drs2p in endosomal/TGN compartments, and they co-immunoprecipitated with Drs2p. These cdc50-ts mutants exhibited defects in vesicle transport from early endosomes to the TGN as the cdc50 deletion mutant did. These results suggest that mutant Cdc50 proteins could be complexed with Drs2p, but the resulting Cdc50p–Drs2p complex is functionally defective at the non-permissive temperature. Cdc50p may play an important role for phospholipid translocation by Drs2p. [ABSTRACT FROM PUBLISHER]

Asymmetrical distribution of phospholipids is generally observed in the eukaryotic plasma membrane. Maintenance and changes of this phospholipid asymmetry are regulated by ATP-driven phospholipid translocases. Accumulating evidence indicates that type 4 P-type ATPases (P4-ATPases, also called flippases) translocate phospholipids from the exoplasmic leaflet to the cytoplasmic leaflet of the plasma membrane and internal membranes. Among P-type ATPases, P4-ATPases are unique in that they are associated with a conserved membrane protein of the Cdc50 family as a non-catalytic subunit. Recent studies indicate that flippases are involved in various cellular functions, including transport vesicle formation and cell polarity. In this review, we will focus on the functional aspect of phospholipid flippases. [ABSTRACT FROM PUBLISHER]

Abstract: Using APP NLh /APP NLh x PS-1 P246L /PS-1 P246L human double knock-in (APP/PS-1) mice, we examined whether phosphatidylserine (PtdSer) asymmetry is significantly altered in brain of this familial Alzheimer disease mouse model in an age-dependent manner as a result of oxidative stress, toxic Aβ(1-42) oligomer production, and/or apoptosis. Annexin V (AV) and NBD-PS fluorescence in synaptosomes of wild-type (WT) and APP/PS-1 mice were used to determine PtdSer exposure with age, while Mg2+ ATPase activity was determined to correlate PtdSer asymmetry changes with PtdSer translocase, flippase, activity. AV and NBD-PS results demonstrated significant PtdSer exposure beginning at 9 months compared to 1-month-old WT controls for both assays, a trend that was exacerbated in synaptosomes of APP/PS-1 mice. Decreasing Mg2+ ATPase activity confirms that the age-related loss of PtdSer asymmetry is likely due to loss of flippase activity, more prominent in APP/PS-1 brain. Two-site sandwich ELISA on SDS- and FA-soluble APP/PS-1 brain fractions were conducted to correlate Aβ(1–40) and Aβ(1–42) levels with age-related trends determined from the AV, NBD-PS, and Mg2+ ATPase assays. ELISA revealed a significant increase in both SDS- and FA-soluble Aβ(1–40) and Aβ(1–42) with age, consistent with PtdSer and flippase assay trends. Lastly, because PtdSer exposure is affected by pro-apoptotic caspase-3, levels of both latent and active forms were measured. Western blotting results demonstrated an increase in both active fragments of caspase-3 with age, while levels of pro-caspase-3 decrease. These results are discussed with relevance to loss of lipid asymmetry and consequent neurotoxicity in brain of subjects with Alzheimer disease. [Copyright &y& Elsevier]

The course of malaria does not only depend on the virulence of the parasite Plasmodium but also on properties of host erythrocytes. Here, we show that infection of erythrocytes from human sickle cell trait (HbA/S) carriers with ring stages of P. falciparum led to significantly enhanced PGE2 formation, Ca2+ permeability, annexin-A7 degradation, phosphatidylserine (PS) exposure at the cell surface, and clearance by macrophages. P. berghei-infected erythrocytes from annexin-A7-deficient (annexin-A7-/-) mice were more rapidly cleared than infected wildtype cells. Accordingly, P. berghei-infected annexin-A7-/- mice developed less parasitemia than wildtype mice. The cyclooxygenase inhibitor aspirin decreased erythrocyte PS exposure in infected annexin-A7-/- mice and abolished the differences of parasitemia and survival between the genotypes. Conversely, the PGE2-agonist sulprostone decreased parasitemia and increased survival of wild type mice. In conclusion, PS exposure on erythrocytes results in accelerated clearance of Plasmodium ring stage-infected HbA/S or annexin-A7-/- erythrocytes and thus confers partial protection against malaria in vivo. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

A common feature of all eukaryotic membranes is the non-random distribution of different lipid species in the lipid bilayer (lipid asymmetry). Lipid asymmetry provides the two sides of the plasma membrane with different biophysical properties and influences numerous cellular functions. Alteration of lipid asymmetry plays a prominent role during cell fusion, activation of the coagulation cascade, and recognition and removal of apoptotic cell corpses by macrophages (programmed cell clearance). Here we discuss the origin and maintenance of phospholipid asymmetry, based on recent studies in mammalian systems as well as in Caenhorhabditis elegans and other model organisms, along with emerging evidence for a conserved role of mitochondria in the loss of lipid asymmetry during apoptosis. The functional significance of lipid asymmetry and its disruption during health and disease is also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Pathogenic fungi present a special problem in the clinic as the range of drugs that can be used to treat these types of infections is limited. This situation is further complicated by the presence of robust inducible gene networks encoding different proteins that confer tolerance to many available antifungal drugs. The transcriptional control of these multidrug resistance systems in several key fungi will be discussed. Experiments in the non-pathogenic Saccharomyces cerevisiae have provided much of our current understanding of the molecular framework on which fungal multidrug resistance is built. More recent studies on the important pathogenic Candida species, Candida albicans and Candida glabrata, have provided new insights into the organization of the multidrug resistance systems in these organisms. We will compare the circuitry of multidrug resistance networks in these three organisms and suggest that, in addition to the well-accepted drug efflux activities, the regulation of membrane composition by multidrug resistance proteins provides an important contribution to the resistant phenotypes observed. [Copyright &y& Elsevier]

Abstract: Oxidative stress, a hallmark of Alzheimer disease (AD), has been shown to induce lipid peroxidation and apoptosis disrupting cellular homeostasis. Normally, the aminophospholipid phosphatidylserine (PtdSer) is asymmetrically distributed on the cytosolic leaflet of the lipid bilayer. Under oxidative stress conditions, asymmetry is altered, characterized by the appearance of PtdSer on the outer leaflet, to initiate the first stages of an apoptotic process. PtdSer asymmetry is actively maintained by the ATP-dependent translocase flippase, whose function is inhibited if covalently bound by lipid peroxidation products, 4-hydroxynonenal (HNE) and acrolein, within the membrane bilayer in which they are produced. Additionally, pro-apoptotic proteins Bax and caspase-3 have been implemented in the oxidative modification of PtdSer resulting in subsequent asymmetric collapse, while anti-apoptotic protein Bcl-2 has been found to prevent this process. The current investigation focused on detection of PtdSer on the outer leaflet of the bilayer in synaptosomes from brain of subjects with AD and amnestic mild cognitive impairment (MCI), as well as expression levels of apoptosis-related proteins Bcl-2, Bax, and caspase-3. Fluorescence and Western blot analysis suggest PtdSer exposure on the outer leaflet is significantly increased in brain from subjects with MCI and AD contributing to early apoptotic elevation of pro- and anti-apoptotic proteins and finally neuronal loss. MCI is considered a possible transition point between normal cognitive aging and probable AD. Brain from subjects with MCI is reported to have increased levels of tissue oxidation; therefore, the results of this study could mark the progression of patients with MCI into AD. This study contributes to a model of apoptosis-specific oxidation of phospholipids consistent with the notion that PtdSer exposure is required for apoptotic-cell death. [Copyright &y& Elsevier]

Abstract: Background: The pathophysiological link between increased blood concentrations of factors responsible for the derangement and erythrocyte membrane functions in chronic renal failure (CRF) patients are not thoroughly elucidated. We studied the erythrocyte characteristics and phospholipid asymmetry loss in CRF patients with different grades of uremia and also examined the involvement of intracellular free Ca2+ in early events of apoptosis in uremic erythrocytes. Methods: The studied population consisted of 90, age and sex matched control subjects (Group I) and 238 CRF cases divided into 3 groups (Group II, III and IV) according to urea concentrations and complexity of secondary complications. Erythrocyte membrane fluidity determined by binding of MC540. Intracellular free Ca2+ concentration was determined by the 2-wavelength method by using fluorescent calcium-sensitive probe FURA-2AM. Measurement of erythrocyte phosphatidylserine exposure by flow cytometry using Annexin V-FITC. Results: Cholesterol shedding increased with increasing severity of uremic complications. Erythrocytes from Group II show mild echinocyte or formation of spicules on the erythrocyte membrane surface whereas in Group III and IV they were echinocytic. Binding of MC540 was significantly higher with progression of uremic complications. Surface charge of uremic erythrocyte membrane was significantly reduced when compared with control subjects. Intracellular free Ca2+ was positively correlated with binding of MC540 and surface hydrophobicity. The phosphatidylserine exposure of erythrocytes was significantly higher (p <0.001) in uremic patients when compared with controls. Conclusions: Phosphatidylserine (PS) exposure erythrocytes were significantly increased in uremic patients when compared with controls. Uremic complications predisposes to membrane damages in erythrocytes. [Copyright &y& Elsevier]

Abstract: Lem3p-Dnf1p is a putative aminophospholipid translocase (APLT) complex that is localized to the plasma membrane; Lem3p is required for Dnf1p localization to the plasma membrane. We have identified lem3 mutations, which did not affect formation or localization of the Lem3p-Dnf1p complex, but caused a synthetic growth defect with the null mutation of CDC50, a structurally and functionally redundant homologue of LEM3. Interestingly, these lem3 mutants exhibited nearly normal levels of NBD-labeled phospholipid internalization across the plasma membrane, suggesting that Lem3p may have other functions in addition to regulation of the putative APLT activity of Dnf1p at the plasma membrane. Similarly, deletion of the COOH-terminal cytoplasmic region of Dnf1p affected neither the localization nor the APLT activity of Dnf1p at the plasma membrane, but caused a growth defect in the cdc50Δ background. Our results suggest that the Lem3p-Dnf1p complex may play a role distinct from its plasma membrane APLT activity when it substitutes for the Cdc50p-Drs2p complex, its redundant partner in the endosomal/trans-Golgi network compartments. [Copyright &y& Elsevier]

Abstract: The maintenance of phospholipid asymmetry in membrane bilayers is a paradigm in cell biology. However, the mechanisms and proteins involved in phospholipid translocation are still poorly understood. Members of the type 4 subfamily of P-type ATPases have been implicated in the translocation of phospholipids from the outer to the inner leaflet of membrane bilayers. In humans, several inherited disorders have been identified which are associated with loci harboring type 4 P-type ATPase genes. Up to now, one inherited disorder, Byler disease or progressive familial intrahepatic cholestasis type 1 (PFIC1), has been directly linked to mutations in a type 4 P-type ATPase gene. How the absence of an aminophospholipid translocase activity relates to this severe disease is, however, still unclear. Studies in the yeast Saccharomyces cerevisiae have recently identified important roles for type 4 P-type ATPases in intracellular membrane- and protein-trafficking events. These processes require an (amino)phospholipid translocase activity to initiate budding or fusion of membrane vesicles from or with other membranes. The studies in yeast have greatly contributed to our cell biological insight in membrane dynamics and intracellular-trafficking events; if this knowledge can be translated to mammalian cells and organs, it will help to elucidate the molecular mechanisms which underlie severe inherited human diseases such as Byler disease. [Copyright &y& Elsevier]

In rats rendered hypercholesterolaemic by maintaining them on a cholesterol-enriched diet (0??5 %) for 8 weeks, as a result of alteration in membrane structural lipids, erythrocytes were observed to be deformed and become more fragile. This deformity and fragility was partially reversed by the two dietary spice principles, curcumin and capsaicin, and the spice, garlic, by virtue of their ability to lower the extent of hypercholesterolaemia. A further insight into the factors that might have reduced the fluidity of erythrocytes in hypercholesterolaemic rats revealed changes in fatty acid profile of the membranes, phospholipid composition of the membrane bilayer, reduced Ca2+, Mg2+-ATPase, and reduction in the sensitivity of erythrocytes to concanavaline A. Dietary capsaicin appeared to counter these changes partially in hypercholesterolaemic rats. Electron spin resonance (ESR) spectra and fluorescence anisotropy parameters also revealed altered fluidity of erythrocytes in hypercholesterolaemic rats. Dietary capsaicin and curcumin significantly reversed this alteration. Scanning electron microscopic examination revealed that the echinocyte population was increased in the erythrocytes of hypercholesterolaemic rats, and this was significantly countered by dietary capsaicin. The membrane protein profile and the active cation efflux appeared to be unaffected in the hypercholesterolaemic situation. [ABSTRACT FROM PUBLISHER]

A series of Zn2+–2,2′-dipicolylamine (Zn2+–DPA) coordination complexes with an attached NBD fluorophore are synthesized and evaluated as fluorescent sensors. The sensors do not respond to vesicles composed of zwitterionic phosphatidylcholine, but the NBD fluorescence emission is enhanced in the presence of anionic vesicles. A sensor with two Zn2+–DPA units and a hydrophilic tris(ethyleneoxy) linker produced a larger emission enhancement than an analogue with a butyl linker, and titration with 1:1 POPC:POPS vesicles lead to an apparent phospholipid association constant of 5.3×104M-1. The sensor can detect the presence of vesicles containing as little as 5% phosphatidylserine. The sensing effect apparently requires a membrane surface because the sensors do not respond to a phosphatidylserine derivative that is monodispersed in aqueous solution. [Copyright &y& Elsevier]

Pscudosubstrates and inhibitors of ATPases were studied with respect to their capability to modulate the kinetic behavior of Mg2+ -ATPase and aminophospholipid translocation in red blood cell ghosts. ATP was substituted by the pseudosubstrates of P-type ATPases acetyl phosphate and p-nitrophenyl phosphate. With both pseudosubstrates, aminophospholipid translocation from the outer to the inner leaflets of resealed erythrocyte ghosts could be observed, although with a significantly decreased velocity compared to. that in presence of ATP. both with respect to phosphate hydrolysis and translocation. Similarly, the apparent affinities for the pseudosubstrates were much lower than for ATP. Among the inhibitors studied. suramin acted as a competitive inhibitor of ATP towards both Mg2+-ATPase activity and aminophospholipid transiocation. However. the inhibition of translocation occurred at a higher inhibitor concentration than the inhibition of Mg2+-ATPase activity. With elaiophylin, only a partial inhibition of Mg2+-ATPase activity could be detected, but translocation of labeled phosphatidylserine was almost completely abolished. With eosin Y, .an almost complete inhibition of both Mg2+-ATPase activity and translocation could be achieved. The observed responses of aminophospholipid translocation to ATPase inhibitors strongly suggest that a P-type ATPase, part of which displays a Mg2+-ATPase activity, is involved in aminophospholipid translocation. [ABSTRACT FROM AUTHOR]

A model is presented to simulate transverse lipid movement in the human erythrocyte membrane. The model is based on a system of differential equations describing the time-dependence of phospholipid redistribution and the steady state distribution between the inner and outer membrane monolayer. It takes into account several mechanisms of translocation: (i) ATP-dependent transport via the aminophospholipid translocase; (ii) protein-mediated facilitated and (iii) carrier independent transbilayer diffusion. A reasonable modelling of the known lipid asymmetry could only be achieved by introducing mechanism (iii). We have called this pathway the compensatory flux, which is proportional to the gradient of phospholipids between both membrane leaflets. Using realistic model parameters, the model allows the calculation of the transbilayer motion and distribution of endogenous phospholipids of the human erythrocyte membrane for several biologically relevant conditions. Moreover, the model can also be applied to experiments usually performed to assess phospholipid redistribution in biological membranes. Thus, it is possible to simulate transbilayer motion of exogenously added phospholipid analogues in erythrocyte membranes. Those experiments have been carried out here in parallel using spin labeled lipid analogues. The general application of this model to other membrane systems is outlined. [ABSTRACT FROM AUTHOR]

The physical properties of lipid bilayers with a similar composition to the outer and inner leaflets of the human erythrocyte membrane have been examined in protein-free model systems. The outer leaflet (OL) was represented by a phospholipid mixture containing phosphatidylcholine and sphingomyelin extracted from human erythrocytes, while a mixture of phosphatidylcholine, phosphatidylserine and phosphatidylethanolamine represented the inner leaflet (IL). The ratio of cholesterol to phospholipid was varied in both mixtures. The lateral diffusion coefficient of fluorescent phospholipids diluted in such lipid mixtures was determined by the modulated fringe pattern photobleaching technique. Contrast curves with a single exponential decay, indicative of homogeneous samples, were obtained only for temperatures above 15 °C and for a cholesterol to phospholipid molar ratio below 0.8. The rate of lateral diffusion was approximately five times faster in IL than in OL multilayers, in agreement with former results obtained in human erythrocytes (Morrot et al. 1986). Varying the cholesterol to phospholipid ratio from 0 to 0.8 (mol/mol) enabled us to decrease the diffusion constant by only a factor of approximately 2 for both IL and OL mixtures. The order parameter of a spin-labeled phospholipid was determined in the different systems and found to be systematically smaller in IL mixtures than in OL mixtures. The present study indicates that the difference in lipid diffusivity of the two erythrocyte leaflets may be accounted for solely by a difference in phospholipid composition, and may be independent of cholesterol and protein asymmetry. [ABSTRACT FROM AUTHOR]

Organization of dynamic cellular structure is crucial for a variety of cellular functions. In this study, we report that Drosophila and Aedes have highly elastic cell membranes with extremely low membrane tension and high resistance to mechanical stress. In contrast to other eukaryotic cells, phospholipids are symmetrically distributed between the bilayer leaflets of the insect plasma membrane, where phospholipid scramblase (XKR) that disrupts the lipid asymmetry is constitutively active. We also demonstrate that XKR-facilitated phospholipid scrambling promotes the deformability of cell membranes by regulating both actin cortex dynamics and mechanical properties of the phospholipid bilayer. Moreover, XKR-mediated construction of elastic cell membranes is essential for hemocyte circulation in the Drosophila cardiovascular system. Deformation of mammalian cells is also enhanced by the expression of Aedes XKR, and thus phospholipid scrambling may contribute to formation of highly deformable cell membranes in a variety of living eukaryotic cells. [Display omitted] • Compared with mammalian cells, Drosophila cells have a highly elastic cell membrane • Drosophila XKR promotes membrane deformation by constitutive phospholipid scrambling • Phospholipid scrambling affects actin cortex dynamics and lipid bilayer mechanics • Deformability of mammalian cells can also be enhanced by phospholipid scrambling Shiomi et al. show that Drosophila cells possess a cell membrane with extreme deformability and resistance to mechanical stress, where constitutively active phospholipid scramblase XKR disturbs the asymmetric distribution of phospholipids and promotes the deformability of cell membranes by regulating both actin cortex dynamics and mechanical properties of the phospholipid bilayer. [ABSTRACT FROM AUTHOR]